EWRS Physical and Cultural Weed Control Working Group

Transcription

Europäische Gesellschaft
für Herbologie
EUROPEAN
WEED
RESEARCH
SOCIETY
Société Européenne
de Malherbologie
Proceedings
5th EWRS Workshop on
Physical and Cultural Weed Control
Pisa, Italy
scuola superiore
Sant'Anna
di studi universitari e di perfezionamento
11-13 March 2002
The Proceedings were compiled and produced by
Daniel C. Cloutier
Institut de malherbologie
P.O. Box 222
Sainte-Anne-de-Bellevue
(Québec) H9X 3R9
Canada
Tel. 514-630-4658
Fax 514-695-2365
E-mail: wm@ewrs.org
Scientific organisers
Dr Paolo Bàrberi
Scuola Superiore Sant'Anna di Studi Universitari e di Perfezionamento
Classe di Scienze Sperimentali - Settore di Scienze Agrarie
P.za Martiri della Libertà 33
56127 Pisa, Italy
Tel. +39-050-883.448/9
Fax +39-050-883.215
E-mail: barberi@sssup.it
Web: www.sssup.it/~barberi/index.htm
Dr Daniel C. Cloutier
Institut de malherbologie
P.O. Box 222
Sainte-Anne-de-Bellevue
(Québec) H9X 3R9
Canada
Tel. 514-630-4658
Fax 514-695-2365
E-mail: wm@ewrs.org
Produced February 19, 2002, corrected March 31, 2003
ii
Local organisers
Dr Paolo Bàrberi
56127 Pisa, Italy
Tel. +39-050-883.448/9
Fax +39-050-883.215
E-mail: barberi@sssup.it
Web: www.sssup.it/~barberi/index.htm
Dr Marco Ginanni
Centro Interdipartimentale di Ricerche Agro-ambientali "E. Avanzi"
Università di Pisa
Via Vecchia di Marina 6
56010 S. Piero a Grado (PI), Italy
Tel. +39-050-96.35.32
Fax +39-050-96.03.30
E-mail: ginanni@tiscalinet.it
Camilla Moonen
56127 Pisa, Italy
Tel.+39-050-883.448/9
Fax +39-050-883.215
E-mail: moonen@sssup.it
Prof. Andrea Peruzzi
Dipartimento di Agronomia e Gestione dell'Agro-ecosistema - Settore
Meccanica Agraria
Università di Pisa
Via S. Michele degli Scalzi 2
56124 Pisa, Italy
Tel. +39-050-59.92.63
Fax +39-050-54.06.33
E-mail: aperuzzi@agr.unipi.it
Dr. Michele Raffaelli
Dipartimento di Agronomia e Gestione dell'Agro-ecosistema - Settore
Meccanica Agraria
Università di Pisa
Via S. Michele degli Scalzi 2
56124 Pisa, Italy
Tel. +39-050-59.92.66
Fax +39-050-54.06.33
E-mail: mraffaelli@agr.unipi.it
iii
Table of contents
Preventive/cultural weed control and weed community dynamics . . . . . . . . . . . 1
Weed growth and control as influenced by soyabean row spacing and soil
tillage for seed bed preparation
Francesco Vidotto, Aldo Ferrero, Roberto Busi, Anna Saglia . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Simple innovations to improve the effect of the false seedbed technique
R.Y. van der Weide, P.O. Bleeker and L.A.P. Lotz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Assessment of cropping system effects on weed management
using matrix population models
Adam S. Davis and Matt Liebman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Computer model for simulating the long-term dynamics of annual
weeds under different cultivation practices
I.A. Rasmussen, N. Holst, L. Petersen, K. Rasmussen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Optimization of cultivation timing by using a weed emergence model
Maryse L. Leblanc and Daniel C. Cloutier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Effect of the combination of the stale seedbed technique with cultivations
on weed control in maize
Daniel C. Cloutier and Maryse L. Leblanc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Mechanical and physical weed control in maize
P. Balsari, G. Airoldi, A. Ferrero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Analysis of weeds succession and competitiveness as related to the
sowing date and another crop techniques of sugar beet
G. Campagna, G. Rapparini . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Influence of fallow land-use intensity on weed dynamics and crop
yield in southern Cameroon
M. Ngobo, S. Weise and M. McDonald . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Effects of crop density, spatial uniformity and weed species
on competition with spring wheat Triticum aestivum.
Jannie Maj Olsen, Lars Kristensen, Hans-Werner Griepentrog and Jacob Weiner . . . . . . . . . . . 45
Preventive weed control in lower input farming system
V. Pilipavicius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
The effects of cultural practices on crop and weed growth in organic spring oats
B. R. Taylor and D. Younie . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
iv
Effect of crop competition and cultural practices on the growth of Sonchus arvensis
P. Vanhala, T. Lötjönen & J. Salonen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
The action spectrum for maximal photosensitivity of germination and significance for
lightless tillage
K. M. Hartmann & A. Mollwo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
A degree-day model of Cirsium arvense predicting shoot emergence from root buds
R. K. Jensen, D. Archer & F. Forcella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Weediness in 40- year period without herbicide
L. Zarina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Inter- and intra-row mechanical weed control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Relationship between speed, soil movement into the cereal row and
intra-row weed control efficacy by weed harrowing
A. Cirujeda, B. Melander, K. Rasmussen, I. A. Rasmussen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Experiences and experiments with new intra-row weeders
Piet Bleeker, Rommie van der Weide and Dirk Kurstjens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
An experimental study of lateral positional accuracy achieved during
inter-row cultivation.
M C W Home, N D Tillett, T Hague, R J Godwin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Weed control by a rolling cultivator in potatoes
Karsten Rasmussen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Options for mechanical weed control in string bean – work parameters and crop yield
M. Raffaelli, P. Bàrberi, A. Peruzzi & M. Ginanni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Mechanical intra-row weed control in organic onion production
J. Ascard & F. Fogelberg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Experiences related to the use of the weeding harrow and of the roll-star cultivator in
Emilia-Romagna for weed control on hard and common wheat, sunflower and soyabean in
organic agriculture
L. Dal Re and A. Innocenti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
Physical methods for weed control in potatoes
J.A. Ivany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Different combinations of weed management methods in organic carrot
L. Radics, I. Gál, P. Pusztai . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Options for mechanical weed control in grain maize – effects on weeds
v
Options for mechanical weed control in grain maize - work parameters and crop yield
M. Raffaelli, A. Peruzzi, P. Bàrberi & M. Ginanni . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Options for mechanical weed control in string bean – effects on weeds
Preliminary results on physical weed control in spinach
Tei F., Stagnari F., Granier A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Cover crops, intercrops, mulches, manure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Impacts of composted swine manure on maize and three annual weed species
M. Liebman, T. Richard, D.N. Sundberg, D.D. Buhler, and F.D. Menalled . . . . . . . . . . . . . . . 173
Cover crops and mulches for weed control in organically grown vegetables
Lars Olav Brandsæter and Hugh Riley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
The role of cover cropping in renovating poor performing paddocks
Frances Hoyle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
Managing intercrops to minimise weeds
H.C. Lee & S. Lopez-Ridaura . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Impact of composted swine manure on crop and weed establishment and growth
Fabián D. Menalled, Matt Liebman, and Douglas D. Buhler . . . . . . . . . . . . . . . . . . . . . . . . . . 183
A system-oriented approach to the study of weed suppression
by cover crops and their residues
A.C. Moonen & P. Bàrberi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
Comparison of different mulching methods for weed control
in organic green bean and tomato
L. Radics & E. Székelyné Bognár . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
No-tillage of arable crops into living mulches in Switzerland
Bernhard Streit, Juerg Hiltbrunner, Lucia Bloch and David Dubois . . . . . . . . . . . . . . . . . . . . . 205
Water and steam for weed control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
Preliminary studies in the comparison of hot water and hot foam for weed control.
R. M. Collins, A. Bertram, J-A. Roche, & M. E. Scott . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Band-steaming for intra-row weed control
B. Melander, T. Heisel & M. H. Jørgensen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Development of innovative machines for soil disinfection
by means of steam and substances in exothermic reaction
A. Peruzzi, M. Raffaelli, M. Ginanni, M. Mainardi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
vi
Soil steaming with an innovative machine – effects on the weed seedbank
A.C. Moonen, P. Bàrberi, M. Raffaelli, M. Mainardi, A. Peruzzi & M. Mazzoncini . . . . . . . . 230
Water-jet cutting for weed control
F. Fogelberg & A. Blom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Soil steaming with an innovative machine – effects on actual weed flora
P. Bàrberi, A.C. Moonen, M. Raffaelli, A. Peruzzi, P. Belloni & M. Mainardi . . . . . . . . . . . . 238
Hot water for weed control on urban hard surface areas
D. Hansson . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Thermal control of Vicia hirsuta and Vicia tetrasperma in winter cereals
P. Juroszek, M. Berg, P. Lukashyk, U. Köpke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
Thermal weed control by water steam
A. Sirvydas, P. Lazauskas , R. Vasinauskien, P. Kerpauskas . . . . . . . . . . . . . . . . . . . . . . . . . 253
Methodology and research in physical and cultural weed control . . . . . . . . . . 263
Effect of plant dry mass on uprooting by intra-row weeders
D.A.G. Kurstjens, G.D. Vermeulen & P.O. Bleeker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
Evaluation of Physical Weeders
J. Meyer, N. Laun, B. Lenski . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Effect of cutting height on weed regrowth
S. Baerveldt and J. Ascard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
Yield effect of distance between plants and cutting of weeds
T. Heisel, C. Andreasen & S. Christensen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Semi-automatic machine guidance system
J. Meyer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
Experimental assessment of the elements for the design of
a microwave prototype for weed control
C. De Zanche, F. Amistà, and S. Beria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
Video assessment techniques to monitor physical weed management
N. M. Bromet and J.N.Tullberg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
vii
5th EWRS Workshop on Physical Weed Control
Pisa, Italy, 11-13 March 2002
Preventive/cultural weed control and weed community dynamics
1
2
Weed growth and control as influenced by soyabean row spacing
and soil tillage for seed bed preparation
Francesco Vidotto1, Aldo Ferrero1, Roberto Busi1, Anna Saglia2
1
Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio, Università degli Studi di
Torino, Via Leonardo Da Vinci, 44 – 10095 Grugliasco- Italy.
2
Regione Piemonte - Settore Fitosanitario, C.so Grosseto 71/6 – 10147 Torino
Abstract
This research was aimed at studying the effect of soyabean planting arrangement on efficacy of
mechanical weed control. The following combinations of row spacing and weed control
interventions were compared: 1) 15 cm and 1 or 2 harrowings; 2) 30 cm and 1 or 2 harrowings; 3)
75 cm and 1 or 2 harrowings + inter-row tillage. All treatments were tested in soil subject to
ploughing or minimum tillage for seed bed preparation. Harrowing was carried out on total plot
surface by means of a harrow equipped with flexible tines. Inter-row tillage was performed with a
rotary harrow. Main weeds recorded before mechanical weed control were AMARE, ECHCG,
POLPE and POROL. AMARE density determined in plots subject to minimum tillage was more
than twice that assessed in ploughed plots. Greatest efficacy of weed control (about 95%) was
obtained in plots were soyabean was planted at 75 cm, even if in these conditions grain yield was
significantly lower than that recorded in other plots with closer rows.
3
Simple innovations to improve the effect of the false seedbed technique
R.Y. van der Weide1, P.O. Bleeker1 and L.A.P. Lotz2
Applied Plant Research, P.O. Box 430, 8200 AK Lelystad, The Netherlands
2
Plant Research International, P.O.box 16, 6700 AA Wageningen, The Netherlands
Email: r.y.van.der.weide@ppo.dlo.nl; p.bleeker@ppo.dlo.nl; l.a.p.lotz@plant.wag-ur.nl
1
Objective
In crops cultivated without the use of herbicides, preventive methods can be useful to decrease
the weed problem. The effects of the false seedbed technique varies with the method and timing
used. Research to increase the insight in the efficacy of this technique is presented in this paper.
Method
In several field experiments the effects of false seedbeds at the weed density and the total weed
control have been counted. Varying factors in these experiments were the time and length of the
false seedbed and the method of cultivating the soil after the false seedbed. Research of the method
included the effect of covering the machinery used and/or the effect of additional farred light under
the cover.
Research and discussion
Weed species which germinate relative early can be suppressed by a false seedbed before
sowing and/or late sowing of silage maïze in the Netherlands (see table 1). Late germinating species
as for example Echinocloa crus galli and Solanum nigrum however, can even be stimulated by late
sowing. A false seedbed sometimes also increase the density of these warmed loving species. This
especially occurred in a relative cold period during the false seedbed as for example in may 1996
where the mean soil temperature was 2 oC lower than in the other years.
Table 1. Percentage decrease (-) or increase (+) of different weed species in silage maïze caused by
relative late sowing (half may in stead of end april) or caused by the use of the false
seedbed technique.
Weed species
Year
Number/m2
after early
sowing*
Effect (in % increase or decrease) by:
late sowing
Echinchloa crus galli
Chenopodium album
Stellaria media
Polygonum persicaria
Poa annua
Atriplex patula
Solanum nigrum
*
'96
'97
'98
'96
'97
'96
'97
'97
'96
'98
'99
'99
'96
'99
3.8
105.0
213.7**
15.0
22.7
13.5
53.3
69.3
18.3
326.0**
10.0
1.7
6.0
233.3
in untreated fields without false seedbed
+ 260
+ 68
+
+
+
+
-
**
40
30
2
2
2
57
- 77
- 82
- 12
+ 104
after late sowing
false seedbed before
early sowing
late sowing
+400
+150
- 78
- 82
- 66
- 45
- 49
- 81
- 92
- 28
- 39
- 86
- 99
- 33
- 50
- 43
- 27
- 48
- 30
- 57
- 24
- 100
- 50
- 37
- 31
- 70
4
The technique of false seedbed can be improved by covering the machinery used by destroying the
emerged weeds around crop sowing time (see Figure 1). In iceberg lettuce only coverring the
machinery gave 60% less weeds (see table 2).
Table 2. The effect of a false seedbed and/or coverring the machinery used for destroying the
emerged weeds at the soil at the (relative) weed density (data PPO Lelystad).
False seedbed
No
4 weeks
Emerged
weeds
controlled by
Covered
machinery
Rotory
harrow
No
Glyfosate
Rotory
harrow
Yes
No
No
% reduction in number of weeds*
1999
0 (28,0)1
2000
0 (52,5)1
2001
0 (45,5)1
69
44
63
68
60
69
74
71
Yes
74
73
81
No
74
53
85
Yes
71
91
*
relative to plantbedpreparation without false seedbed and without covering the machinery
1
number of weeds / m2 around 6 weeks after preparation of true seed/plantbed
Hoeing
Figure 1. Covered rotary harrow used the destroy weeds on the false seedbed experiment before
planting iceberg lettuce.
5
Assessment of cropping system effects on weed management
using matrix population models
Adam S. Davis and Matt Liebman
Department of Agronomy, Iowa State University, Ames, IA, 50011-1010, USA
Abstract
Cropping system characteristics can influence weed prevention efforts by altering key demographic
rates of weeds. Our objective was to combine empirical and modeling methods to assess cropping
system effects on weed population growth rate (O). In a field experiment conducted in 2000 and
2001 in Boone, IA, Setaria faberi (giant foxtail) was grown in a wheat-corn-soybean crop sequence.
Wheat was grown either as a sole-crop (‘RC-‘) or as an intercrop with red clover (‘RC+’). Six
demographic parameters were measured for S. faberi in the two crop sequences, including seed
survival from October to March (ss(OM)) and March to October (ss(MO)), germination (g), plant
survival (sp), fecundity (f) and seed survival of post-dispersal predation (ss(pred)). These parameters
were used in a periodic matrix model of cropping system effects on S. faberi population dynamics.
For each of the three phases of the crop sequence, sub-annual transition matrices described
recruitment, plant survival, reproduction, post-dispersal seed predation and overwinter seedbank
decline.
Retrospective perturbation analysis of a model examines the correspondence between the sensitivity
of O to a particular parameter and the amount of variation observed in that parameter. We adapted
the Life Table Response Experiment (LTRE) approach to retrospective perturbation analysis to
include periodic matrix models. There was a two-fold difference in O ('O) between the RCtreatment (O = 2.5) and the RC+ treatment (O = 1.2). We decomposed 'O into contributions from
each of the parameters in the periodic model. Three parameters accounted for 94% of the
contributions to 'O: ss(pred) in the wheat phase (-0.56), and g in the corn (-0.43) and wheat (-0.33)
phases. Post-dispersal predation of S. faberi seeds was the parameter that O was most sensitive to in
each of the phases of the crop sequence. Daily seed removal rate did not differ between the RCand RC+ treatments in the soybean (5.5%) and corn (17.5%) phases, whereas there was a two-fold
difference in daily seed removal rates between the RC- (22.5%) and the RC+ (60%) treatments in
the wheat phase. Analysis of periodic matrix models using the modified LTRE design should help
guide the design and improvement of future weed prevention systems.
6
Computer model for simulating the long-term dynamics
of annual weeds under different cultivation practices
I.A. Rasmussen, N. Holst, L. Petersen, K. Rasmussen
Department of Crop Protection
Danish Institute of Agricultural Sciences,
Research Centre Flakkebjerg,
DK-4200 Slagelse, Denmark
Abstract
A model is being developed which describes the population dynamics of annual weeds and how it is
affected by crop rotation, cultivation practices and weed control. The model aims to predict the
development of a certain weed species in order to plan crop rotation and cultivation practices to
minimize the risk of proliferation. The model does not predict the exact number of weeds expected
to be found in a certain year or crop, but rather the general development over a number of years.
The model includes documented knowledge, as well as informal expert knowledge, on seed survival
in the soil, seed placement in soil after tillage, seed germination with respect to placement in soil,
time of year and tillage, weed development in response to crop competitiveness and seed production
of the weeds. The model is at present only accounting for the development of one weed species at a
time, and only a few weed species are parameterised. However, the model can easily be extended
with more weed species, crops and cultivation practices. Model predictions should match what
knowledgeable weed scientists already know, perhaps with a little new insight.
Introduction
Weed control alone is not always enough to prevent proliferation of a certain weed species.
This is particularly the case in organic farming, where the efficacy of mechanical weed control
often is low. Because of this, many preventive methods including tillage, crop rotation,
augmentation of the competitiveness of the crop against the weed, sowing time and harvest time etc.
are included in the weed control strategy – particularly in organic farming (Kropff et al. 2000;
Rasmussen et al. 2000).
A diversified crop rotation can prevent proliferation of a single weed species, since the
demands of most weed species in terms of germination, growth and propagation cannot be met if
sowing time, crop growth and harvest time are varied between years. An example is that winter
annual species germinate primarily in the fall and their establishment is less successful in springsown crops than in crops sown in the fall. Experiments have shown that some of the problems with
grass weeds, which can arise in crop rotations dominated by winter cereals, can be alleviated by
incorporating larger proportions of spring cereals in the rotation (Melander 1993).
The competitiveness of the crop against the weeds is a very important parameter for the growth
and propagation of the weeds. Choice of cultivar, seed rate, quality of the seedbed, row distance and
geometrical arrangement, fertiliser level and fertiliser application/placement are among the most
important factors influencing crop competitiveness (Espeby 1989; Kropff & van Laar 1993;
Christensen & Rasmussen 1996; Weiner et al. 2001).
7
There are many possibilities to prevent weed problems, but they have to be planned well in
advance. Optimally, for a certain crop rotation, there would be a strategy for the utilisation of
preventive methods within that crop rotation. The need for direct control should be restricted to as
little as possible. However, it is quite complicated to characterize the way the different methods
interact in the crop rotation and how the crop rotation itself may influence the weed proliferation.
In order to illustrate this, a computer model has been developed which describes the
development of different annual weed species under different scenarios. The purpose of the model
is to define the development in order to choose the best management to avoid proliferation of a
certain weed. The model does not attempt to predict the exact number of weeds likely to germinate
in any certain year, but to predict a general trend in the development over a course of several years.
As such, it is not a decision support system to plan control in a given crop, but a management
support system to plan crop rotation and other cultural measures to decrease reliance on high
control efficacy.
Materials and Methods
Modelling approach
Several models have been published, which describe the proliferation of field weeds (Cousens
& Mortimer 1995). The system components and processes incorporated in these models reflect the
interest of the modeller and the purpose of the model and include soil seed bank, germination,
establishment, growth, competition, and seed production. Most of these models work in time steps
of one year and under the common assumption that all individuals of a weed species germinate and
shed seeds at the same time. Such models are well suited to describe the proliferation of a weed
under uniform cropping conditions, such as grass weed propagation in no-till, continuous winter
cereals. In contrast, models with a finer time step can capture the variation within a year. Most weed
species emerge and shed seeds unevenly through the year; for example, new emergence is often
seen after rain or tillage. Within a competitive crop, latecomers will suffer a high mortality thus
depleting the soil seed bank, whereas in less competitive crops, plants are more likely to thrive and
eventually contribute to the seed bank. To grasp such within-year processes, models with a time
step finer than one year are needed. Thus Christensen et al. (1999), based upon the matrix model
approach of Silvertown (1987), developed a model that operated in time steps of 14 days. This
facilitated the modelling of weed cohorts, having emerged at different times through the year, and
the effect of various control measures in different crop rotations could be predicted based upon the
knowledge put into the model.
The model presented here is a continuation of this line of work. As a guideline for model
design, we wish to keep it simple so that it can easily be extended with additional weed species,
crops and cultivation practices. At the same time, we wish to maintain the overall realism so that the
model can offer guidance on weed management through targeted planning of cropping cycle and
cultivation practices. Model predictions should match what knowledgeable weeds scientists already
know, perhaps with a little surprise and new insight now and then.
Weed life stages
Our weed model is stage-structured (Fig. 1) and incorporates each life stage as a separate subpopulation: number of seeds in or on the ground, or still fastened to the plant; number of emerging
seedlings; number and mass of plants in the vegetative and the reproductive growth stage. In the
first version of the model, the population dynamics of each weed species is considered separately
with no inter-specific competition other than between crop and weed. The time step of the model is
8
1 day. The vertical distribution of seeds in the soil is kept in 20 1-cm layers. Seed dormancy takes
many forms (Baskin & Baskin 1998) but only primary dormancy is included directly in the model.
Soil tillage and seed germination
During tillage seeds will be shifted around among the 20 soil layers (the seeds on the soil
surface follow those in the top 1-cm layer). Cousens & Moss (1990) formulated two models of the
movement of seeds caused by harrowing and ploughing, respectively. We use their equations
directly in our model considering the seed bank split into four 5-cm layers as they did. In the case of
shallower treatments, we simply scale down the thickness of the layers and apply the same
equations, e.g., for ploughing at 16 cm depth, the four layers would each be considered 4 cm thick.
Mechanical weed control, which properly operated only disturb the top cm of the soil, is assumed
not to shift seeds around, except mixing seeds from the soil surface into the top layer.
In undisturbed soil seeds will perish at a rate specific to the species. In the model we use the
mortality rates determined by Chancellor (1986), which leads to an exponential decrease in seed
numbers. For lack of knowledge we assumed mortality rates to apply equally to seeds at all soil
depths. For seeds upon the soil surface we assumed a fixed mortality rate per day-degree common
to all species. This mortality is thought primarily to be caused by non-specific predation by insects
and birds.
Figure 1. Weed life stages and processes included in the model. The population density of different
life stages is kept in either individuals per m2 (N) or in biomass dry-weight per m2 (M).
9
1.0
0.9
Viola arvensis
Chamomilla recutita
Polygonum persicaria
Relative germination
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
1
2
3
4
5
6
7
8
9
10
Soil depth (cm)
Figure 2. Seed emergence depending on soil depth summarised by log-normal curves (data after
Chancellor 1964).
1.0
Chamomilla recutita
Stellaria media
0.9
Relative germination
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Figure 3. Phenology of seed germination (data after Chancellor 1986).
Nov
Dec
10
The germination rate of seeds depends on their vertical position in the soil, as described by
Chancellor (1964). Based on his data we could summarise for each species the relative germination
rate according to depth by a log-normal curve (Fig. 2). Furthermore, the propensity of seeds to
germinate varies with the season. Sophisticated models of germination have been developed,
incorporating the effects of soil temperature and humidity (Forcella 1998; Forcella et al. 2000) and
dormancy (Vleeshouwers 1997; Benech-Arnold et al. 2000). However, we chose a simpler
approach, because we are interested only in the typical course over the year of the weed life cycle
and how it interacts with the typical timing of cultivation practices. Thus the phenology of
germination was described, for each species, by a relative measure of germination for each calendar
month, linearly interpolated to yield daily values (Fig. 3). These species-specific germination curves
were determined by experts based on formal (Håkansson 1983; Chancellor 1986) and informal
knowledge.
The number of seeds germinating from a certain soil layer on a specific date can now be
obtained be multiplying the two relative rates (from Figs. 2 and 3) with the germination rate in
undisturbed soil specific to the weed species. On dates when the soil is disturbed (to a certain depth
by a certain cultivation practice), additional germination will occur. This is calculated multiplying
the two relative rates with the maximum germination rate (determined experimentally under optimal
conditions).
Weed growth and reproduction
The development through the life stages, emergence, vegetative and reproductive growth (Fig.
1), is modelled on a day-degree scale. For simplicity, competition is modelled for mass only, and
numbers are translated into the projected final weed biomass, as plants leave the seedling stage and
enter the vegetative stage.
The final biomass of the weed is calculated by multiplying the effect of intra-specific
competition (Fig. 4) with the effect of the crop (Fig. 5), on the day the weeds shift from the
emergence to the vegetative growth stage. The relation for intra-specific competition (Fig. 4)
concerns the total number of seedlings emerging and not just those emerging on a single day. The
effect of taking this into account is that those that emerge first are allotted a larger share of the final
biomass than those that emerge later, which makes sense biologically.
60
Final weed mass (g dw m-2)
50
40
30
20
10
0
0
20
40
60
Seedling density (plants per m2)
80
100
Figure 4. Example of how final,
maximum weed biomass is
calculated from seedling density.
Final weed biomass -or- Crop competiveness
11
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Relative final weed biomass
Relative current crop competiveness
Dec
Figure 5. The phenology of
crop competitiveness in a field
with a spring-sown followed
by an autumn-sown crop
(dotted line), and the relative
final biomass that the weed
population would achieve if it
emerged at a certain date (full
line).
Seed production is assumed to happen at a fixed daily rate, specific to each species, which is
proportional to the weed mass in the reproductive stage (Rasmussen 1993; Wilson et al. 1995).
Weed mortality caused by cultural practices
The effect of cultural practices depends on the mode of intervention (seeding, harrowing,
ploughing, herbicide treatment, various mechanical weed control methods) and the life stage of the
weed; seeds are unaffected (other than vertical movement: from plant to soil, from surface into soil,
and between layers within soil), seedlings are the most sensitive, plants in the vegetative growth
stage less sensitive, and reproductive plants the least sensitive. Effects are specified as the
percentage mortality caused by each kind of cultural practice for each of the three susceptible life
stages. In addition, the mortality caused by harvesting (removal) on seeds still on the plant can be
specified.
Parameters for the model
Currently, model parameters are being estimated from literature data or, when information is
lacking, from informal expert knowledge. Important literature sources include (Stevens 1932;
Chancellor 1964; Holm et al. 1991; Moss 1985; Chancellor 1986; Legere & Deschenes 1989;
Milberg 1990; Cousens & Moss 1990; Baskin & Baskin 1998; Bouwmeester 2001).
Evaluation of the model
At this early stage, the only evaluation carried out on the model is an expert panel assessing the
results retrieved from the runs of the model under different scenarios. However, a great body of data
from experiments over a long period of time with a record of crop rotation and cultivations, some
with and without weed control, chemical as well as mechanical, will later be used to evaluate the
model in a more objective manner.
Results
At the workshop, the model will be presented, and some examples of scenarios will be shown.
The current version of model can be downloaded from www.agrsci.dk/plb/nho/fieldweeds.htm.
12
Acknowledgements
This work is supported by a grant from The Danish Directorate for Food, Fisheries and Agro
Business.
References
BASKIN CC & BASKIN JM (1998) Seeds - Ecology, Biogeography, and Evolution of Dormancy
and Germination. Academic Press, San Diego, California.
BENECH-ARNOLD RL, SÁNCHEZ RA, FORCELLA F, KRUK BC, & GHERSA CM (2000)
Environmental control of dormancy in weed seed banks in soil. Field crops research 67, 105122.
BOUWMEESTER HJ (2001) The effect of environmental conditions on the annual dormancy
pattern of seeds of Spergula arvensis. Canadian Journal of Botany 71, 64-73.
CHANCELLOR RJ (1964) The depth of weed seed germination in the field. In: Proceedings of the
7th British Weed Control Conference, 606-613.
CHANCELLOR RJ (1986) Decline of arable weed seeds during 20 years in soil under grass and the
periodicity of seedling emergence after cultivation. Journal of Applied Ecology 23, 631-637.
CHRISTENSEN S & RASMUSSEN G (1996) Crop-weed competition and choice of variety, seed
rate and drilling date in winter wheat (Original title: Konkurrence mellem afgrøde og ukrudt i
relation til sortsvalg, såmængder og såtider i vinterhvede. With English summary). In: 13.
Danske Planteværnskonference, Ukrudt, SP-rapport nr. 3, 103-112.
CHRISTENSEN S, RASMUSSEN K, MELANDER B & RASMUSSEN G (1999) Weed
management in organic crop rotations. (Original title: Forebyggelse og regulering af ukrudt i
økologiske sædskifter. With English summary) In: 16. Danske Planteværnskonference,
Plantebeskyttelse i økologisk jordbrug, sygdomme og skadedyr. DJF Rapport Markbrug nr. 10,
41-53.
COUSENS R & MORTIMER M (1995) Dynamics of Weed Populations. Cambridge University
Press, Cambridge, UK.
COUSENS R & MOSS SR (1990) A model of the effects of cultivation on the vertical distribution
of weed seeds within the soil. Weed Research 30, 61-70.
ESPEBY L (1989) Germination of weed seeds and competition in stands of weeds and barley.
Influences of mineral nutrients. Crop Production Science, Sveriges lantbruksuniversitet, 6, 1172.
FORCELLA F (1998) Real-time assessment of seed dormancy and seedling growth for weed
management. Seed science research 8, 201-209.
FORCELLA F, BENECH-ARNOLD RL, SANCHEZ R & GHERSA CM (2000) Modelling
seedling emergence. Field crops research 67, 123-139.
HÅKANSSON S (1983) Seasonal variation in the emergence of annual weeds - an introductory
investigation in Sweden. Weed Research 23, 313-324.
HOLM LG, PLUCKNETT DL, PANCHO JV & HERBERGER JP (1991) The World’s Worst
Weeds, Distribution and Biology. Krieger Publishing Company, Malabar, Florida.
KROPFF MJ, BAUMANN DT, BASTIAANS L (2000) Dealing with weeds in organic agriculture
– challenge and cutting edge in weed management. In: Proceedings 13th IFOAM Scientific
Conference: IFOAM 2000: the world grows organic, Basel, 175-177.
KROPFF MJ & VAN LAAR HH (1993) Modelling crop-weed interactions. CAB International,
Walingford, UK.
13
LEGERE A & DESCHENES JM (1989) Effects of time of emergence, population density and
interspecific competition on Hemp-Nettle (Galeopsis tetrahit) seed production. Canadian
Journal of Plant Science 69, 185-194.
MELANDER B (1993) Population dynamics of Apera spica-venti as influenced by cultural
methods. Brighton Crop Protection Conference – Weeds, 107-112.
MILBERG P (1990) Hur länge kan ett frö leva? (With English summary) Svensk botanisk tidskrift
84, 323-351.
MOSS SR (1985) The survival of Alopecurus myosuroides Huds. seeds in soil. Weed Research 25,
201-211.
RASMUSSEN IA (1993) Seed production of Chenopodium album in spring barley sprayed with
different herbicides in normal to very low doses. In: 8th EWRS Symposium "Quantitative
approaches in weed and herbicide research and their practical application", Braunschweig,
639-646.
RASMUSSEN IA, MELANDER B, RASMUSSEN K et al. (2000) Recent advances in weed
management in cereals in Denmark. In: Proceedings 13th IFOAM Scientific Conference:
IFOAM 2000: the world grows organic, Basel, 178.
SILVERTOWN J (1987) Introduction to Plant Population Ecology. Longman Scientific &
Technical, Essex.
STEVENS OA (1932) The number and weight of seeds produced by weeds. American Journal of
Botany 19, 784-794.
VLEESHOUWERS LM (1997) Modelling weed emergence patterns. PhD thesis, Wageningen
Agricultural University.
WEINER J, GRIEPENTROG H-W & KRISTENSEN L (2001) Suppression of weeds by spring
wheat Triticum aestivum increases with crop density and spatial uniformity. Journal of applied
ecology 38, 784-790.
WILSON BJ, WRIGHT KJ, BRAIN P, CLEMENTS M & STEPHENS E (1995) Predicting the
competitive effects of weed and crop density on weed biomass, weed seed production and crop
yield in wheat. Weed Research 35, 265-278.
14
Optimization of cultivation timing by using a weed emergence model
Maryse L. Leblanc1 and Daniel C. Cloutier2
Institut de Recherche et de Développement en Agroenvironnement, P.O. Box 480, SaintHyacinthe, Québec, Canada J2S 7B8; E-mail: maryse.leblanc@irda.qc.ca
2
Institut de malherbologie, P.O. Box 222, Sainte-Anne-de-Bellevue, Québec, Canada H9X 3R9.
E-mail: daniel.cloutier@videotron.ca
1
In agriculture, weeds are very important since without crop protection, almost half of the
world’s actual agricultural production would be lost (Vleeshouwers 1997). Due to this potential
risk, growers developed an approach where weeds are controlled by systematically applying
herbicide, regardless of whether it is needed or not. Herbicides have become dominant in many
production systems resulting in environmental contamination and in the development of herbicide
resistance (Beckie et al. 2001). Recognizing the problem, many governments in the world promote
integrate weed management systems which minimize the use of herbicides by combining biological
and physical controls with appropriate farming practices (Panneton et al. 2001).
In the current context in agriculture, integrated weed management systems emphasizes
integration of techniques to anticipate and manage problems rather than react to them after they
appear (Buhler 2001). As part of these systems, it is critical to treat weeds at the best time to
optimize resources and time. Therefore, a predictive model of the timing of weed emergence
becomes an essential tool in integrated weed management program. Common lambsquarters
(Chenopodium album L.) was the species that was selected first to develop and validate our weed
emergence model approach (Leblanc 2001).
Common lambsquarters, widely distributed
throughout the world, is the most common weed encountered in cropping systems grown in
temperate zones (Bassett and Crompton 1978; Leblanc 2001).
In the model development process, most of the viable common lambsquarters seeds are
assumed to be non dormant in the spring since their dormancy should have been released by the low
winter temperatures under Québec climatic conditions. The timing of seed germination and seedling
emergence from a non dormant population of seeds is mostly regulated by the soil environment
where temperature and water content are the two main factors (King and Oliver 1984).
Germination is primarily influenced by soil temperature and moisture whereas pre-emergence
growth is under the control of soil temperature (Leblanc et al. 1998; Roman et al. 1999;
Vleeshouwers 1997). Under Québec spring conditions, soil water content does not appear to be a
limiting factor for common lambsquarters emergence since snow melting in the spring supplies the
soil reserves. Consequently, there is generally enough water from April to June for common
lambsquarters emergence (Leblanc 2001). In Québec, temperature is a more important factor in the
spring than soil moisture in regulating the emergence of common lambsquarters.
Several weed emergence models have been developed based on the accumulation of thermal
time (degree days) but the use of a single base temperature might result in the over- or
underestimation of the thermal time units required for the emergence of a given proportion of the
population when there are differences in field management (Oryokot et al. 1997; Roman et al.
2000). The use of a single base temperature to describe the complete seed population germination
might also introduce some artefacts since it was observed that seeds had different thermal
requirement for germination and a lower base temperature will not be adequate for cohorts that
germinate later in the season (Dumur et al. 1990). Based on these statements, a mathematical model
to predict common lambsquarters seedling emergence in relation to air cumulative thermal units (C
degree days) was developed in Québec from endemic field weed populations. One of the
15
assumptions of the model was that air temperature exchange is very rapid at the depth from which
lambsquarters seedlings emerge and is closely related to the temperature of sandy soils in the spring
(Leblanc 2001).
It was also observed in a laboratory experiment that the percentage of weed germination
increased with temperature (Leblanc 2001). Within a weed species, it appears that there is
variability in the thermal requirement of individual seeds. Those that germinate earliest in the
season have lower requirements than those that germinate later. If the soil is disturbed, by seedbed
preparation or cultivation for example, the disturbance will kill emerged and emerging seedlings,
leaving behind seeds with higher thermal requirements (base temperature). Therefore, the model
was built on the assumption that thermal requirements for emergence increases as the proportion of
the emerged population increases, indicating that the base temperature becomes higher as the crop
seedbed preparation date is delayed. The same concept could be applied on cultivation operations
since they destroy the emerged fraction of weed population.
The equation of the relationship between the cumulative proportion of the total seedling
emergence over the growing season and the cumulative air thermal units was a modified Weibull
function of the following form:
CPE
1 e
§ CTU ATb CTU 0 · s
ln( 2 ) ¨
¸
© CTU 50 CTU 0 ¹
[1]
where CPE is the cumulative proportion of emergence, CTUATb is the cumulative thermal units with
adjusted base temperature (ATb) to the seedbed preparation date, CTU0 is the cumulative thermal
units at emergence initiation, CTU50 is the cumulative thermal units to mid-emergence, and s is the
shape parameter (Leblanc 2001).
The cumulative thermal units in degree days were calculated by using the double sine method
which consists of using two sine curves fitted to the minimum and maximum temperature for a day
and the minimum temperature for the next day (Allen 1976). The starting date (biofix date) of the
thermal unit accumulation was set to be the day when the average soil temperatures at a 5-cm depth
reached the base temperature. The model was calibrated for different seedbed preparation dates and
soil texture by adjusting the base temperature to the cumulative air thermal units at seedbed
preparation date and to the soil mineral fraction.
An excellent prediction of the cumulative proportion of seedling emergence was obtained with
the calibrated model. The model validation was subsequently done by using data collected
independently during two years at a site located 80 km away from the original experimental area.
There were no differences between observed and predicted values. This model can be considered to
be fully validated for the conditions under which it was originally developed. The model provided a
good fit for the field data and accurately predicted the cumulative emergence as a function of day of
the year for both experimental years.
The model was originally calibrated and validated for seedbed preparation times but the
concept can be extended to cultivation timing. This model can be used to plan cultivation timings
instead of having to scout fields on a regular basis or instead of using a calendar basis. The weed
control decisions can be based on the proportion of common lambsquarters that has emerged since
the selectivity varies between cultivators. Common lambsquaters was used as an example to
16
develop the thermal time approach for weed emergence but it could easily be adapted to other weed
species whose emergence is limited by low spring temperature in temperate climate.
References
ALLEN, J. C. 1976. A modified sine wave method for calculating degree days. Environ. Entomol.
5:388-396.
BASSET, I. J. & C. W. CROMPTON. 1978. The biology of Canadian weeds. 32. Chenopodium
album L. Can. J. Plant Sci. 58:1061-1072.
BECKIE, H. J., L. M. HALL, & F. J. TARDIF. 2001. Herbicide resistance - where are we at today?
Pages 1-36 in R. E. Blackshaw and L. M. Hall, eds. Integrated weed management: explore the
potential. Expert Committee on Weeds, Ste-Anne-de-Bellevue, Québec, Canada.
BUHLER, D. D. 2001. Developing integrated weed management systems. Pages 37-46 in R. E.
Blackshaw and L. M. Hall, eds. Integrated weed management: explore the potential. Expert
Committee on Weeds, Ste-Anne-de-Bellevue, Québec, Canada.
DUMUR D., C. J. PILBEAM, & J. CRAIGON. 1990. Use of the Weibull function to calculate
cardinal temperatures in Faba bean. J. Exp. Bot. 41:1423-1430.
KING, C. A. & L. R. OLIVER. 1984. A model for predicting large crabgrass (Digitaria
sanguinalis) emergence as influenced by temperature and water potential. Weed Sci. 32:561567.
LEBLANC, M. L. 2001. Modeling weed emergence as influenced by environmental conditions in
corn in southwestern Québec. PhD thesis, McGill University, Ste-Anne-de-Bellevue, Québec,
Canada.176 p.
LEBLANC, M. L., D. C. CLOUTIER, G. D. LEROUX, & C. HAMEL. 1998. Facteurs impliqués
dans la levée des mauvaises herbes au champ. Phytoprotection 79(3):111-127.
ORYOKOT, J. O. E., S. D. MURPHY, & C. J. SWANTON. 1997. Effect of tillage and corn on
pigweed (Amaranthus spp.) seedling emergence and density. Weed Sci. 45:120-126.
PANNETON, B., C. VINCENT, & F. FLEURAT-LESSARD. 2001. Plant protection and physical
control methods, the need to protect crop plants. Pages 9-32 in C. Vincent, B. Panneton, and F.
Fleurat-Lessard, eds. Physical control methods in plant protection. Springer-Verlag, Berlin
Heidelberg, Germany, INRA, Paris, France.
ROMAN, E. S., A. G. THOMAS, S. D. MURPHY, & C. J. SWANTON. 1999. Modeling
germination and seedling elongation of common lambsquarters (Chenopodium album). Weed
Sci. 47:149-155.
ROMAN, E. S., S. D. MURPHY & C. J. SWANTON. 2000. Simulation of Chenopodium album
emergence. Weed Sci. 48:217-224.
VLEESHOUWERS, L. 1997. Modelling weed emergence patterns. PhD thesis, Wageningen
Agricultural University, Wageningen, Netherlands. 165 p.
17
Effect of the combination of the stale seedebd technique
with cultivations on weed control in maize
Daniel C. Cloutier1 and Maryse L. Leblanc2
1
Institut de malherbologie, P.O. Box 222, Sainte-Anne-de-Bellevue, Québec, Canada H9X 3R9.
E-mail: daniel.cloutier@videotron.ca
2
Institut de Recherche et de Développement en Agroenvironnement, P.O. Box 480, SaintHyacinthe, Québec, Canada J2S 7B8; E-mail: maryse.leblanc@irda.qc.ca
Abstract
Annual weed density was decreased by 67% in the stale seedbed technique compared to the
conventional production system, without using any weed control measures. The pattern of
emergence of the annual weeds remained the same but shifted in time, with a smaller amplitude.
The maximum of emergence was twice as small as that of the conventional seedbed preparation.
Mechanical cultivation in the stale seedbed treatment decreased the weed population level to 20%
of the initial level. Maize yield was not affected by the delayed seeding in the stale seedbed.
However, maize grain moisture content was 2% greater in the stale seedbed. This could increase
production costs since it might require a longer drying period. Using a maize hybrid that reaches
maturity earlier might alleviate this disadvantage and it might also decrease production risks in the
advent of adverse weather conditions.
18
Mechanical and physical weed control in maize
P. Balsari (1), G. Airoldi (1), A. Ferrero (2)
( ) Dipartimento di Economia e Ingegneria Agraria, Forestale e Ambientale - Università di Torino
Via Leonardo da Vinci, 44 - 10095 Grugliasco (Torino)
E-mail: Paolo.Balsari@unito.it , Gianfranco.Airoldi@unito.it
(2) Dipartimento di Agronomia e Gestione del Territorio Agricolo - Università di Torino
Via Leonardo da Vinci, 44 - 10095 Grugliasco (Torino)
E-mail: Aldo.Ferrero@unito.it
1
Abstract
Different weed control techniques, based on the use of mechanical means integrated with
flaming band applications, were compared in a two-year experiment into an organic farm in the
western Po Valley.
The control of the grown between the rows was obtained through hoeing and ridging, while
flaming and spring teeth harrowing were used to control the weeds in the rows. The crop was
planted at the end of May, both years, in three different systems of seed-bed preparation: minimum
tillage, false seeding and ploughing just before planting. The main weeds found in the experimental
plots were: Amaranthus retroflexux L., Polygonum persicaria L., Chenopodium Album L.,
Echinochloa crus-galli L.. The number of treatments was the same for the different seed-bed
preparation techniques, but varied from year to year according to the degree of infestation. Interrow cultivators were used at 4-7 leaves of maize, which was ridged at 9-11 leaves. The flame hoe
was used at 4-6 leaves and at 7-8 leaves to control weeds at the base of the stalk, while a spring
teeth harrow was used at 2-5 leaves.
The differences in the seed bed preparation greatly influenced both the weed development and
crop yield which, respectively, obtained the highest and the lowest result in the minimum tillage.
All the weed control techniques obtained results that were not statistically different, as regards the
weed control, but which were nearly always near 85%, as was the crop yield, which was on average
7,5 Mgss ha-1.
From the economic and operative point of view, a great difference was found according to the
implement that was used for the control. The flexible tine harrow resulted in the highest field
capacity, thanks to the wide working width and the high speed, and was exactly the opposite of
flame cultivator. The latter was also characterized by a considerable variable in costs, due to gas
consumption.
Introduction
The use of physical and mechanical means (such as hoeing, ridging and flaming) allows, if
properly planned and managed, the control of weeds in row crops that is similar to that obtained by
chemicals (Balsari et. Al., 1989; Balsari et. Al. 1991; Peruzzi et Al., 1997). Mechanical
interventions, however, require that the soil is in good workable conditions, and this mainly
depends on the weather conditions, the physical characteristics and preparation of the soil.
When these weed control techniques are used, the preventive means of control applied during
the seed bed preparation phase and at planting take on great importance. The planning of postemergence weed control also has to take account of the selectivity towards the crop of the means of
control, the time required, costs of intervention and the efficacy against weeds (Balsari et. Al.,
1990; 1993; Anken et. Al., 1999).
19
An experiment was carried out in 2000 and 2001 to try to resolve these problems; the scope of
the experiment was to compare some of the techniques that were used for the control of weeds and
which are based on different mechanical + physical interventions and using different time
strategies.
The experiment was carried out in the western Po Valley, on a farm that began organic hoeing
in 1997 and which is characterised by a loam soil.
Preventive weed control was planned in detail to reduce potential crop infestation and direct
weed control was then introduced at the crop post-emergence stage through selective interventions.
In the first season (the year 2000) the preventive weed control was based on ploughing and disk
harrowing (26 April) then, due to weather conditions, which was characterized by frequent rainfall,
it was not possible to use the disk harrow on the ploughed soil for real early seed bed preparation,
which was limited to early ploughing. The machine was used a second time (25 May) on the areas
worked by disk harrow. A rotary harrow completed the seed bed preparation (27 May) both on the
ploughed and disk harrowed soils, just before crop planting.
In the second season (the year 2001) the preventive weed control was based on the
interventions that are reported in table 1.
Seed bed preparation
Machine used and intervention
time
Early seed bed preparation minimum tillage:
Disk harrow (3 April)
Disk harrow (22 May)
Rotary harrow and planter (31 May)
Early seed bed preparation traditional ploughing:
Plough (6 April)
Disk harrow (9 April)
Seed bed preparation just before
planting:
Plough (24 May)
Table 1 - Interventions for preventive weed control carried out in the year 2001.
In both seasons, a hybrid FAO 600 class was planted with a distance of 75 cm between the
rows and at a distance of 19 cm between the seeds, with initial density of 7 plants m-2.
Selective weed control in post emergence was based on different physical and mechanical
techniques, as reported in table 2.
20
Season 2000
Season 2001
1 - control plots
1 - control plots
2 - flaming + hoeing (5^-6^ leaf) (20 June)
ridging (8^-9^ leaf) (4 July)
hoeing (8^-9^ leaf) (27 June)
flaming + ridging (8^-9^ leaf) (4 July)
flaming + hoeing (8^-9^ leaf) (27 June)
4 - hoeing (5^-6^ leaf) (20 June)
4 - hoeing n (4^-5^ leaf) (14 June)
5 - ridging (8^-9^ leaf) (4 July)
5 - hoeing (4^-5^ leaf) (14 June)
6 - spring teeth harrowing (3^ leaf) (8 June)
spring teeth harrowing (4^-5^ leaf) (14 June)
7 - spring teeth harrowing (3^ leaf) (8 June)
spring teeth harrowing (4^-5^ leaf) (14 June)
Table 2 - Techniques used for the crop post emergence selective weed control.
A randomized block design with 360 m2 plots (30m x 12 m - 16 maize rows) was used.
Machines used.
Seed-bed preparation.
Farm machines linked to a 4WD 95 kW tractor were used for the ploughing and disk
harrowing. A two-bottom two-way integral-mounted mouldboard plough was used for the first
operation, operating at a depth of 40 cm and at a speed of 6 km h-1; a 2.5 wide tandem disk harrow
was used for the second operation - operating at a depth of 15 cm and at a speed of 9 km h-1.
A contractor's machines were used for both harrowing and maize planting. The rotary harrow 5.8 m wide and linked to a 110 kW 4WD tractor - operated at e depth of 15 cm and at a speed of 5
km h-1. The four-row pneumatic planter was linked to a 55 kW 2WD tractor and operated at a speed
of 8 km h-1.
Post emergence weed control
A 4 m, fixed frame, spring-toothed harrow was used, linked to a 60 kW 4WD tractor; it
operated at e depth of 2-3 cm and at a speed of 3 km h-1 in the first treatment and a speed of 5
km h-1 in the second one (fig. 1).
First intervention.
Detail of the crop
Figure 1 - The spring teeth harrow used in the trials.
21
A four-row farm machine, linked to a 2WD 44 kW tractor was used for hoeing and ridging.
The machine is made up of a series of working elements mounted on parallelograms with a
gauge wheel for a constant working depth.
Each parallelogram was equipped with 5 'S'-shaped spring teeth for hoeing. In the early
treatment, each spring teeth set was equipped with two shields for crop protection. In this way the
machine was able to operate at a depth of 4-6 cm and at a speed of 6 km h-1, allowing weed control
of 80% of the soil, leaving an untreated band of just 9 cm along each side of the row (fig. 2).
Figure 2 - Effect of the hoeing .
Each parallelogram was equipped with 2 'S'-shaped spring teeth and a high-wing mouldboard
furrower for the ridging. During the treatment care was taken to bury as many weeds as possible
along the row and this lead to a reduction of the velocity to 4 km h-1 and required a working depth
of 8 cm (about 16 cm between the top of the ridge and the bottom of the furrow - fig. 3).
Figure 3 - Effect of ridging.
The flaming equipment consists of a frame and 6 parallelograms with height adjusting wheels.
Each parallelogram has two 25 cm long burners, that were adjustable in height and inclination
above the ground. The burners were supplied by LP- Gas, in 10 kg gas cylinders, through a circuit
with a pressure regulator and a minimum and maximum adjustment tap that can be activated
directly by the tractor drivers. Each burner is fitted with a thermovalve that interrupts the supply of
gas whenever the flame is accidentally extinguished. The machine was used with gas at 300 kPa
and with a field speed of 3 km h-1. Eight burners (2 for each row) were used in post emergence,
operating near the base of the stalk, burning the weeds on a 25 cm band that was not controlled with
hoeing and ridging (fig. 4).
22
First intervention.
Second intervention.
Figure 4 - The machine used for flaming.
Assessment of the weeds
The degree of infestation was determined for the different treatments in 4 different periods in
both season at these stages:
- before passage of the rotary harrow (before crop planting);
- before the first intervention against weeds (4^-6^ maize leaf);
- after all the interventions against weeds (at maize raising);
- before harvesting.
The density of the weeds was assessed for each determination, on at least 4 areas of 0,25 m2 in
each plot.
Assessment of the crop
At crop maturity, the following parameters were determined:
final crop density;
maize plant height;
incidence of abnormal, lodged and broken maize plant;
maize yield and dry matter content in grains.
The results were elaborated and all the data were subjected to factorial ANOVA. The means
were separated using Duncan's test at a 0.05% level.
Results
The year 2000 - Assesment of the weeds
A mean weed density of 136 plants m-2 was recorded before the intervention of the rotary
harrow in the early ploughed area with a density of 29 plants m-2 in the minimum tillage area.
The main weeds in the ploughed soil were Chenopodium polyspermum L., Amaranthus
retroflexus L. and Chenopodium album L.. Amaranthus retroflexus, Vicia sativa L., Chenopodium
polyspermum L. and Portulaca oleracea L. were prevalent in the minimum tillage soil (fig. 5).
23
others
16.3
Vicia sativa
2.0
Stellaria media
2.6
Papaver rhoeas
3.8
Vicia sativa
4.4
Lolium spp.
2.0
5.4
Capsella bursa-pastoris
3.8
Portulaca oleracea
10.9
6.7
Amaranthus retroflexus
12.2
21.8
3.8
Chenopodium spp.
0.0
10.0
69.4
20.0
30.0
40.0
50.0
60.0
70.0
80.0
Weed density (plants m-2)
Early ploughing
Minimum tillage
Figure 5 - The year 2000. Weed density before rotary harrowing.
Just before the first intervention against the weeds, the total weed density was in the range of
13.3 and 26.3 plants m-2, with no significant differences between the different seed bed preparation
techniques. The prevalent species were Amaranthus retroflexus, Chenopodium album, Echinochloa
crus-galli L. and Portulaca oleracea (fig. 6).
10.6
Echinochloa crusgalli
4.0
7.5
Portulaca oleracea
4.0
13.5
Amaranthus
retroflexus
10.5
6.0
Chenopodium spp.
7.8
0.0
2.0
4.0
6.0
8.0
10.0
Weed density (plants
Early ploughing
12.0
14.0
16.0
m-2)
Minimum tillage
Figure 6 - The year 2000. Density of the different species before the first intervention of weed
control.
The weed density, 11 days after the last intervention for weed control, ranged from 72,7 to
141,1 plants m-2. The infestation level did not seem to be affected by the seed bed preparation
techniques.
Of the different species, there was a higher presence of only Chenopodium album in the
ploughed soil (fig. 7).
24
2.0
1.0
44.0
Portulaca oleracea
52.0
27.0
Amaranthus
retroflexus
21.0
3.0
Chenopodium spp.
21.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
Early ploughing
Minimum tillage
Figure 7 - The year 2000. Mean density of the weeds in the control plots 11 days after the
mechanical interventions for the weed control.
The efficacy of post-emergence weed control techniques always proved to be good (fig. 8),
both as regards the amount of weeds that were present and the different species, and ranged from 97
to 100%. The best results were obtained by flaming, even though the statistical analysis does not
show any significant difference for the different treatments.
Weed control (% of untreated plots)
95
96
97
98
99
100
flaming + hoeing
ridging
flaming + hoeing
flaming + ridging
hoeing
ridging
ridging
Early ploughing
Minimum tillage
Figure 8 - The year 2000. Weed control expressed as a reduction of the plants in relation to the
control plots after weed control intervention. The values refer to the entire number of weeds that
were present.
The presence of weeds at harvesting was significantly higher (38 plants m-2 in the control plots)
in the minimum tillage areas with a prevalent presence of Amaranthus retroflexus, Portulaca
oleracea and Echinochloa crus-galli, while Chenopodium album was found to be prevalent in the
early ploughed areas (fig. 9).
25
2.5
1.5
9.0
Portulaca oleracea
8.0
19.0
Amaranthus
retroflexus
11.5
3.0
Chenopodium spp.
14.0
0.0
5.0
10.0
15.0
20.0
Early ploughing
Minimum tillage
Figure 9 - The year 2000. Mean density of weeds in the control plots at harvesting.
As in the previous determination, all the compared weed control techniques were characterized
by a good efficacy level with no significant differences among them. The best weed control was
obtained from the flaming applications, with a weed control of nearly 100% in both the single and
double treatments (fig. 10). The flaming in fact allowed a reduction of the weed development
throughout the entire maize growing season, while mechanical (hoeing and ridging) led to a late
development of weeds. The ridging alone only allowed a acceptable weed control in the early
ploughed areas.
0
20
40
60
80
100
flaming + hoeing
ridging
flaming + hoeing
flaming + ridging
hoeing
ridging
ridging
Early ploughing
Minimum tillage
Figura 10 - The year 2000. Weed control as a reduction of the plants in relation to the control plots
at harvesting. The values refer to the entire number of weeds that were present.
The year 2001 - Assesment of the weeds
Before intervention with the rotary harrow, a mean weed density of 22.4 plants m-2 was
recorded in the areas in which the seed bed was prepared just before planting - with the prevalent
presence of Capsella bursa pastoris L., Amaranthus spp., Chenopodium album, Poyigonum
persicaria L., Plantago major L. and Stellaria media Cyr. - a density of 5.7 plants m-2 in the early
seed bed preparation linked to the minimum tillage - with a prevalent presence of Amaranthus spp.
26
and Chenopodium spp. - and 0.4 plants m-2 in the early seed bed preparation linked to the traditional
ploughing (fig. 11).
0.4
Polygonum persicaria 0.0
26.4
0.0
Plantago major 0.0
15.6
3.2
Stellaria media 0.0
0.0
Echinichloa crus-galli 0.0
14.8
6.4
Chenopodium polyspermum 0.2
0.0
8.4
Chenopodium album 0.0
26.8
6.4
Capsella bursa-pastoris 0.0
47.6
2.0
Others 0.0
0
52.4
16.0
3.0
Amaranthus spp.
15.2
11.6
10
20
30
40
50
60
-2
Weed density (plants m )
Just before planting
Early seed bed preparation
Traditional ploughing
Minimum tillage
Figure 11 - The year 2001. Weed density before rotary harrowing.
Just before the first intervention against the weeds, the total weed density was 36.9 plants m-2 in
the early seed bed preparation linked to the minimum tillage, while it ranged from 1.5 to 3.8 plants
m-2 in the other soil preparation techniques. The prevalent species were Amaranthus retroflexus,
Chenopodium album and Echinochloa crus-galli (fig. 12).
28.9
Echinochloa crus-galli
1.1
1.1
5.8
Chenopodium album 0.0
1.9
112.2
4.7
0.6
Others 0.0
0.0
0
20
40
60
80
100
120
Minimum tillage
Figure 12 - The year 2001. Density of the different species before the first weed control
intervention.
The weed density, 8 days after the last intervention for the weed control, ranged from 14.7
plants m-2 in the early seed bed preparation linked to the minimum tillage to 6.8 - 6.6 plants m-2 in
the case of the other seed bed preparation techniques. The main weeds that were present were
Amaranthus retroflexus, Chenopodium album and Echinochloa crus-galli (fig. 13).
27
17.3
1.7
2.0
1.6
Chenopodium polyspermum
15.4
5.5
16.7
Chenopodium album
7.1
13.8
37.2
9.3
11.6
0.4
0.6
0.1
Others
0
10
20
30
40
Minimum tillage
Figure 13 - The year 2001. The mean density of the weeds in the control plots 8 days after the
mechanical weed control intervention.
The efficacy of the post-emergence weed contol techniques ranged from 80 to 100%, except in
the case of hoeing and ridging in the minimum tillage areas. The best results were obtained through
flaming and spring teeth harrowing (fig. 14).
2 spring teeth harrowing
hoeing - ridging
hoeing
2 hoeing
ridging
hoeing
ridging
2 flaming + hoeing
ridging
flaming + hoeing
hoeing - ridging
0%
20%
40%
60%
80%
100%
Minimum tillage
Figure 14 - The year 2001. Weed control expressed as a reduction of the plants in relation to the
control plots after weed control intervention. The values refer to the entire number of weeds that
were present.
The presence of weeds at harvesting was significantly higher (38 plants m-2 in the control plots)
in the minimum tillage areas with the prevalent presence of Amaranthus retroflexus, Echinochloa
crus-galli, and Chenopodium album (fig. 15).
28
16.5
3.1
3.1
2.5
9.4
Chenopodium polyspermum
12.1
7.3
5.4
Chenopodium album
22.1
40.3
13.1
18.4
0.5
0.3
0.3
Others
0
10
20
30
Weed density (plants
40
50
m-2)
Minimum tillage
Figure 15 - The year 2001. The mean density of weeds in untreated plots at harvesting.
The best weed control was obtained through spring teeth harrowing in the areas in which the
seed bed was prepared just before planting, with a weed control of nearly 95-100% in both the
single and double treatments (fig. 16). Flaming in fact led to a reduction of the weed development
throughout the entire maize growing season, while mechanical (hoeing and ridging) led to a late
development of weeds.
hoeing - ridging
hoeing
2 hoeing
ridging
hoeing
ridging
2 flaming + hoeing
ridging
flaming + hoeing
hoeing - ridging
0%
20%
40%
60%
80%
100%
Weed control (% of not treated plots)
Minimum tillage
Figure 16 - 2001. Weed control expressed as a reduction of plants in relation to the control plots at
harvesting. The values refer to the whole amount of weeds that were present.
The year 2000 - Assessment of the maize
Factorial ANOVA showed significant differences between the early ploughed soil and
minimum tillage areas as regards:
29
- final crop density - on average 5.8 plants m-2 in the first situation and 5.6 plants m-2 in the
second;
- plant height - on average 225 cm and 234 cm respectively in the first and in the second case;
- incidence of abnormal and lodged plants - nearly 23% in the minimum tillage areas and 14%
in the early ploughed soil.
The best production (7.9 Mgss ha-1) was reached in the ridged plots. This value is in fact not so
significantly different from that obtained with the weed control techniques compared in the
experimentation which obtained a crop yield of between 7.1 and 7.4 Mgss ha-1. The lower yield
obtained in the control plots, with an average production of nearly 5.3 Mgss ha-1, was instead
significant (fig. 17).
b
control
a
ridging
hoeing
ridging
flaming + hoeing
ridging
flaming + hoeing
flaming + ridging
a
a
a
0
2
4
6
8
Yield (Mgss ha-1)
Figure17 – The year 2000. Crop yield: the effect of the different post-emergence weed control
techniques – the means with the same letters are not statistically different (Duncan's Test P=0,05).
The year 2001 - Assessment of the maize
Factorial ANOVA showed significant differences in this season among the different seed bed
preparation techniques, as regards the final density, plant heights, the incidence of abnormal and
lodged plants and the crop yield. The latter was 4.0 Mgss ha-1, in the case of the early seed bed
preparation with the minimum tillage, a value which is significantly lower than that obtained from
the early seed bed preparation with the traditional ploughing or from the seed bed preparation just
before planting, which is always higher than 7.0 Mgss ha-1 (figura 18).
c
Minimum tillage
b
a
0
2
4
Yield (Mgss
6
8
ha-1)
Figure 18 - The year 2001. Crop yield: the effect of the different preventive weed control techniques
– the means with the same letters are not statistically different (Duncan's Test P = 0.05).
As far as the post emergence weed control is concerned, the best crop yield was obtained with
two interventions of spring teeth harrow followed by an intervention of hoeing and one of ridging
30
with a yield of 7.2 Mgss ha-1. This value was not so significantly different from those obtained from
the other weed control techniques, with yields ranging from 6.4 to 6.9 Mgss ha-1, with the exception
of the one in which only hoeing and ridging were used, which had a yield that was reduced to 6.0
Mgss ha-1. The yield obtained in the control plot with a mean value of 3.5 Mgss ha-1 was
significantly lower (fig. 19).
c
control
hoeing - ridging
a
hoeing
ab
hoeing
ridging
b
2 hoeing
ridging
ab
2 flaming + hoeing
ridging
ab
flaming + hoeing
hoeing - ridging
ab
0
1
2
3
4
5
6
7
8
Yield (Mgss ha-1)
Figure 19 – The year 2001. Crop yield: the effect of the different post-emergence weed control
techniques – the means with the same letters are not statistically different (Duncan's Test P = 0.05).
Discussion
The trial pointed out the importance of a weed control strategy based on the application of the
false seeding technique combined with post-emergence interventions. In our test conditions the
early seed bed preparation with traditional ploughing and disk harrowing was particularly
interesting while the result of the early seed bed preparation with minimum tillage resulted to be
negative.
As far as the crop post-emergence weed control technique is concerned, the results of the use of
spring teeth harrow, in the early growing stage of maize followed by hoeing and ridging proved to
be very interesting. This technique obtained results, both as far as weed control and crop yield are
concerned, that are not significantly different from those obtained through flaming, but with a
considerable advantage from the economic and organisation point of view, due to the lower costs
and higher field capacity.
References
ANKEN T, IRLA E, AMMAN H, HEUSSET J, SCHERRER C (1999) - Travail du sol et mise en place des
cultures. Rapports FAT n. 534. Station fédérale de recherches an économie et technologie agricoles
(FAT) Tanikon TG
BALSARI P, AIROLDI G, FERRERO A, MAGGIORE T (1989) Lotta integrata alle malerbe del mais.
Informatore Agrario 45, 61-73.
31
BALSARI P, AIROLDI G, FERRERO A (1990) - Esperienze sulle tecniche a bassa o nulla
chimicizzazione per il controllo delle in festanti del mais. In: Atti II Conferenza Nazionale sul Mais,
Grado, Italia, 412- 422.
BALSARI P, FERRERO A, AIROLDI G (1991) - Weed Control in Maize by Flaming. In: Proceedings of
the 43rd International Symposium on Crop Protection, Gent, Belgium, 681-689.
BALSARI P, AIROLDI G, FERRERO A (1993) Evaluation of the mechanical weed control in maize and
soybean. In: Proceedings of 8th Symposium European Weed Research Society, Braunschweig,
Germany, 341-348.
PERUZZI A, BARBERI P, GINANNI M, RAFFAELLI M, SILVESTRI N (1997) - Prove sperimentali di
controllo meccanico delle infestanti del frumento mediante erpice strigliatore. Atti VI Convegno
Nazionale di Ingegneria Agraria, Ancona, Italia 10-12 Settembre 669-678.
32
Analysis of weeds succession and competitiveness as related to the sowing date
and another crop techniques of sugar beet
G. CAMPAGNA*, G. RAPPARINI
Centro di Fitofarmacia - Dipartimento di Protezione e Valorizzazione Agroalimentare - Università
degli Studi - Via F. Re 8 - 40126 Bologna. *Servizio Agronomico CO.PRO.B.
ABSTRACT
This contribution refers the results obtained by the analysis of a floral succession and
competitiveness as related to the planting date of sugar beet. This study, in a general context of a
reduced environmental impact which expects the abandonment of chemical weed control by
applying organic practices, examined the productivity of the crop sown early in the season in
relation to the crop sown later, by comparing a more traditional complete weed control practice
with a procedure which involves less use of herbicides or with a organic one.
The obtained results of this experiment, carried out in a fine-textured clayey soil, evidenced an
increased crop productivity due to the extension of its life cycle and to the reduction of the
emergence of those macrothermal weeds that are characterised by a graduated and tardy
germination. Although this crop appears to be less infested at the beginning of the life cycle, the
erect stems and the higher degree of competitiveness of Chenopodium album, C. opulifolium, C.
ficifolium, Amaranthus retroflexus, A. albus among dicotyledons ed Echinochloa crus-galli among
gramineae, determined a lower sugar beet productivity.
Sowing early the sugar beet it has been observed a higher level of weed occurrence especially
mesothermal ones, among which the poligonaceae weeds characterised by a horizontal stems, such
as Polygonum aviculare and Fallopia convolvulus, are dominant. The high weed infestation initially
seems to cause disadvantage to the crop, while subsequently it represents under the crop leaves a
grass layer that hinders the germination of the more competitive and tardy weeds, such as
chenopodiaceae and amarantaceae.
Besides, by using weed control techniques in which insecticides are not applied as in the case of
organic practices and procedures characterised by a reduced environmental impact, an early
occurrence of Gatroidea poligoni is enhanced. This coleopter beetle attacks these polygonaceae and
thus can limit the growth and the competitiveness of these two invasive weeds.
Key words: sugar beet, herbicides, sowing date, weeds, organic crop.
Introduction
Over the last decade, in Italy manual weeding has been gradually completely replaced by
chemical weed control. On sugar beet, this practice has been rationalised to an extent unequalled on
any other crop. This has led to a decrease in the herbicide doses used per hectare and thus to a
reduction in environmental impact (Meriggi et al., 2000). The introduction of triflusulphuron
methyl, the aid of new formulative technologies and agronomic crop management using the stale
seed bed technique, mechanical weeding between rows, early sowing, etc., have contributed to the
optimisation of weed control in this specialist crop. There is ever-increasing awareness of the
problems relating to contamination and the possible environmental effects of herbicides, as well as
33
the need to reduce costs and simplify beet growing techniques in order to enhance its
competitiveness. The introduction of genetically modified varieties tolerant of total herbicides,
together with the provision of incentives for the use of integrated weed control systems, could hold
the key to the state of the art in sugar beet weed control (Wevers, 2000). In the meantime, there is a
growing need to introduce growing techniques of low environmental impact, and the prospects for
extending organic farming methods to this industrial crop are increasing. However, sugar beet
grows at slower rates than weeds (Covarelli et al., 1998) and suffers a heavy reduction in yield as a
result of them (Rosso et al., 1996) or as a consequence of incorrect use of weed control techniques
(Campagna et al., 2000). As a result, the need for a more accurate assessment of the effects of weed
competition on sugar beet in relation to sowing period and differentiated growing techniques is
being increasingly felt. This is the aim behind the paper which follows, which sets out to evaluate
this crop's response in terms of productivity to the succession of flora in a typical Italian beetgrowing environment, comparing conventional growing techniques with low chemical impact and
organic farming methods.
Materials and methods (Tab. 1)
The trial was performed at Minerbio in the province of Bologna during 2001, on a fineconsistency clayey soil. The trial field was laid out in randomised blocks repeated 4 times.
Herbicides were applied using a trailed bar fitted with fan nozzles delivering a water volume of 400
L/ha pre-emergence and 200 L/ha post-emergence of the beet. On the organically-grown beet,
finger harrows were used pre-sowing and a mower bar was employed to contain the growth of
erect-stem weeds during the summer. Weeding was carried out when the beet was at the 8-10 leaf
stage. Weed levels were monitored by counting the weeds present in the plots and estimating the %
cover during the crop growth period. The weed biomass was analysed at the end of the growing
cycle. Crop selectivity was evaluated on treated beet plants, which were compared with untreated
plants, on the basis of an empirical scale of 0-10 (0=no symptoms; 10=crop destroyed). When the
beet was harvested, the roots obtained from each plot were weighed.
Weather pattern (Fig. 1): the frequent rainfall which started at the end of the winter and the mild
temperatures were a hindrance to sowing operations and at the same time provided favourable
conditions for the emergence of weeds and for the weed-killing effects of the residual herbicides
applied pre-emergence. The depression which brought very cold air from the North during the
second ten days of April slowed down growth of the weeds and the beet, postponing the start of
post-emergence procedures. On the other hand, in early May, during the final applications on the
crop, temperatures were above the seasonal average. The rainfall during the same period was
favourable for weed-killing operations and for the growth of the crop after the earlier unseasonable
weather, and also favoured late-germinating, late-growing weeds. The hot, dry weather during June
and July led to a below-normal crop growth rate, while the macrothermal weeds continued to
develop.
Results (Tab. 2, 3 – Fig. 2, 3)
The results obtained during the trial conducted in 2001 in a fine-textured clayey soil indicated
that if the sowing period is brought forward to late February, the degree of weed emergence and
infestation is very high, especially during the first part of the growing cycle. The prevalent weeds
were the early-germinating ones, including the creeping polygonaceae such as Polygonum aviculare
and Fallopia convolvulus, as well as Polygonum lapathifolium and Chenopodium album.
34
On the areas sown after the middle of March there was a considerable reduction in the degree
of infestation by Polygonum aviculare and Fallopia convolvulus and to a lesser extent by
Polygonum lapathifolium and Chenopodium album. In the meantime later-germinating weeds,
including Amaranthus retroflexus and Solanum nigrum amongst the dicotyledons and Echinochloa
crus-galli amongst the gramineae appeared, infesting the crop after the initial growth phases of the
beet. In this later sowing period, the treatments performed to eliminate the weeds before emergence
of the crop proved to be of vital importance, especially with regard to the weeds which germinated
during the first half of March, slightly ahead of the beet itself, including polygonaceae and
chenopodiaceae. However, due above all to the particularly mild, wet winter, the extermination of
the weeds which had germinated during autumn and winter and had remained on the seed bed,
including Papaver rhoesas, Sinapis arvensis, Stellaria media and Veronica persica, proved to be
most important.
With the latest sowings at the end of March, we witnessed the almost complete exhaustion of
emergence of Polygonum aviculare and Fallopia convolvulus and only partial exhaustion of
Polygonum lapathifolium and Chenopodium album. As a result of the gaps created in the absence of
weeds and the delay before the development of the later-growing crop, there was an increase in the
germination of macrothermal weeds, especially the more competitive Amaranthus retroflexus,
which enjoyed considerable growth and occupied the space required by the sugar beet.
With the organic growing methods, the floral succession tending to favour the macrothermal
weeds was less obvious, since the use of finger harrows rather than chemical herbicides provided
less radical weed reduction and the effects of the initial complete freeing of the soil were less
noticeable. Weeding between the rows, followed by mowing of the erect weeds standing above the
level of the beet leaves, was found to be vital for the reduction of competition and above all of
dissemination.
Crop yields were higher with earlier sowings, where the growing cycle was longer and the
emergence of later-germinating weeds requiring macrothermal conditions was reduced in favour of
the creeping Polygonaceae. With later sowing dates, infestation levels were lower at the beginning
of the growing cycle, but the erect habit and greater competitiveness shown by the chenopodiaceae
Chenopodium album, C. opulifolium and C. ficifolium, and more especially by the amarantaceae
including Amaranthus retroflexus and to a lesser extent A. albus amongst the dicotyledons, as well
as Echinochloa crus-galli amongst the gramineae, led to a significant reduction in the weight of the
crop's roots.
In the organic crops and also in those farmed by conventional methods with low environmental
impact, where the use of insecticides was not necessary, conditions were favourable for the
occurrence and development of Gastroidea poligoni (Fig. 4), a coleopter beetle which fed mainly
on Polygonum aviculare but also on Fallopia convolvulus, keeping down their growth and thus
their ability to compete, as well as their degree of dissemination. The high degree of infestation by
these 2 invasive weeds in the earliest-sown sugar beet initially appeared to be putting the crop at a
serious disadvantage, but subsequently the grassy layer they formed underneath the leaf system
tended to prevent the emergence of the later-germinating weeds which are also more competitive in
relation to the crop, including chenopodiaceae and amarantaceae, and they were subsequently
almost completely destroyed by this extremely useful insect, leaving room for the crop.
35
Discussion
The study performed on the analysis of the floral succession and the influence of weed
competition in relation to sugar beet productivity on the basis of crop sowing period with
conventional, reduced environmental impact and organic growing methods enabled us to reach the
following conclusions.
With the earliest sowing dates, in spite of the greater initial weed density the sugar beet root
yield was found to be greater. The creeping polygonaceae, Polygonum aviculare and Fallopia
convolvulus, first provided a barrier to the germination of the other weeds, including in particular
the more competitive, erect-growing, later-germinating species such as amarantaceae and summer
gramineae, and were then almost completely destroyed in their turn by the coleopter beetle
Gastroidea poligoni.
With the aid of extermination of the weeds which had germinated on the soil before the later
sowings, the density of polygonaceae and chenopodiaceae, and thus the initial competition the crop
has to face, is considerably reduced, but there is also the risk of increasing the level of infestation
by the more competitive summer-growing amarantaceae and gramineae. What's more, the growing
cycle of the sugar beet, necessary to allow production of the greatest possible quantity of roots
before the arrival of summer with its drought and high temperatures, is reduced.
In the case of the earliest sowings, pre-emergence treatments to reduce initial weed competition
with the crop were found to be extremely useful; the crop can also be aided at a later stage by
mechanical weeding to limit floral competition, and attacks by Gastroidea poligoni to combat the
growth of Polygonum aviculare and Fallopia convolvulus.
With organic growing methods, there are still considerable difficulties due to the problems of
containing weed growth. Full use has to be made of finger harrowing and the exhaustion of seed
germination through early preparation of the seed bed and weeding followed by slight earthing-up,
without over-delaying the sowing period. It is also important to take care that the sugar beet is as
competitive as possible, by reducing germination failure in order to limit weed growth and the
damage arising from competition.
References
CAMPAGNA G., BARTOLINI D., RAPPARINI G., 2000. Ulteriori verifiche di integrazione tra diserbanti di pre e
post-emergenza della barbabietola da zucchero. Atti XII Convegno S.I.R.F.I., 185-189.
CAMPAGNA G., ZAVANELLA M., VECCHI P., MAGRI F., 2000. Sugar beet weed control: yield in relation with
herbicide selectivity and action. Proceedings of the 63rd IIRB Congress, 541-548.
COVARELLI G., ONOFRI A., 1998. Effects of timing of weed removal and emergence in sugar beet. Proceedings: 6th
Mediterranean Symposium EWRS, 65-72.
MERIGGI P., SGATTONI P., 2000. L’ottimizzazione del diserbo nella barbabietola da zucchero. Atti XII Convegno
S.I.R.F.I., 69-91.
ROSSO F., MERIGGI P., PAGANINI U., 1996. Barbabietola da zucchero: tecniche operative per il controllo delle
erbe infestanti. Terra e Vita, 5 (supplemento), 14-19.
WEVERS J.D.A., 2000. Herbicide tolerance and the effects on the environmental contamination. Proceedings of the
63rd IIRB Congress, 179-185.
26-Mar
26-Mar
III
III
7
3
7
6
5
4
3
2
1
3
2
1
glufosinate-ammonium
organic weed-control
-
-
organic weed-control
-
-
-
-
-
-
-
-
-
-
metamitron
metamitron
-
-
metamitron
metamitron
-
metamitron
metamitron
-
3500
2100
-
-
3500
3500
-
3500
3500
-
(ph.+d.+e.) + met. + oil
-
-
-
-
-
-
Subthesis: agronomic practices and weed control applications: products, doses,
etc.
PrePostsowing Pre-emergence
emergence*(1)
Herbicide: g/ha of
A: cotyledons-2
Specific herbicide
a.i.
leaves
-
-
-
-
-
-
-
B: 4 leaves
*(1) Note:
(ph.+d.+e.) = (phenmedipham + desmedipham + ethofumesate) Oil Flow: (52,5+17,5+105) g/ha in A and (75+25+150) g/ha in
B
met. = metamitron: 350 g/ha in A and 490 g/ha in B
oil = mineral oil: 0,3 l/ha
19-Mar
19-Mar
19-Mar
II
II
19-Mar
II
II
19-Mar
II
19-Mar
19-Mar
I
II
26-Feb
I
II
26-Feb
26-Feb
I
Thesis
Tab. 1 - Experimental tests - Year 2001 - Minerbio (BO) Italy
Soil type: 23 % sand; 45 % loam; 32 % clay; pH 8; organic matter 1,7 %
Preeceding crop: wheat
Cultivar: Monodoro (seed treatment with imidacloprid)
8-10 leaves
-
8-10 leaves
8-10 leaves
-
-
-
-
-
-
-
-
inter-row
weeding
Mechanical
end may
end may
mid may
mid may
mid may
mid may
mid may
mid may
mid may
beginning may
beginning may
beginning may
covering
Full
36
Subthes
is
1
2
3
1
2
3
4
5
6
7
3
7
Thesis
I
I
I
II
II
II
II
II
II
II
III
III
4
5
2
1
3
1
4
0
0
0
0
0
ECHCG
27
23
34
4
8
39
34
6
3
45
11
6
CHESS*
9
1
25
2
5
29
22
4
2
48
5
3
POLAV
15
2
44
1
17
56
21
8
1
62
35
5
POLCO
*CHESS=CHEAL, CHEVU, CHEPO, CHEFI
14
32
9
0
6
9
16
2
0
0
0
0
AMARE
in emergence after sowing
16
5
28
3
9
36
22
1
2
41
3
3
POLLA
6
11
3
2
3
3
8
5
3
6
1
0
SOLNI
Tab. 2 - Weed number (in 10 m2 area) before mechanical weeding (30-04-2001)
119
99
178
13
57
219
152
29
13
247
67
22
1
0
1
0
0
39
0
0
0
0
0
0
PAPRH
2
0
3
0
0
5
0
0
0
0
0
0
SINAR
**other weeds: ANGAR, ELIEU, KICSP, VEROF
32
25
35
1
9
47
29
3
2
45
12
5
other**
tot.
broadlea
ves
1
0
2
0
0
3
0
0
0
0
0
0
STEME
1
0
1
0
0
7
0
0
0
0
0
0
VERPE
on the bed sowing without glufosinateammonium
5
0
7
0
0
54
0
0
0
0
0
0
total
37
1
2
3
1
2
3
4
5
6
7
3
7
I
I
I
II
II
II
II
II
II
II
III
III
4
2.7
0.2
1
2
0
1
0.1
1.2
0.2
0.2
0
ECHCG
59
11
0.2
12
55
9
18
0
7
0.1
0
0
AMARE
10
14
0.5
19
18
38
25
0.2
21
1
21
55
CHESS*
5
26
1
1
7
13
1
0.6
37
1.2
5
15
POLLA
2
5
0.2
3
8
21
5
0
18
0.8
7
25
poligonaceae
**
0
2
0
0
0
16
0
0
3
0
0
0
other***
2
1
0.3
2
3
3
3
0.2
2
0.5
2
3
other***
*
*CHESS=CHEALl, CHEVU, CHEPO, CHEFI
**other poligonaceae: POLAV, POLCO
***other weeds from bed sowing: PAPRH, SINAR
****other weeds: AIUCH, ANGAR, ELIEU, EUPSS, KICSP, LACSE, MIAPE, RAPRU, SOLNI, VEROF
Subthesis
Thesi
s
Tab. 3 - Percent of weedy during 30 July 2001
78
59
2.2
37
91
100
52
1
88
3.6
35
98
tot. broad
leaves
38
39
45
40
35
30
25
20
15
10
5
0
45
40
35
30
25
20
15
10
5
0
I
II
III
I
February
II
III
I
March
II
III
I
April
II
III
I
May
rainfall (mm)
II
III
I
June
II
III
July
t° C max
I
II
August
t° C min.
Fig. 1 - Rainfall and temperature in Minerbio from February to August 2001
100
% weedy
80
60
40
in
g
so
w
thesis
30 May
Fig. 2 - Percent of weedy
30 July
7
3
26
-0
3
7
6
5
4
3
19
-0
3
2
1
2
3
in
g
so
w
so
w
in
g
26
-0
2
1
20
0
III
temperature (°C)
rainfall (mm)
40
26
-0
3
in
g
so
w
so
w
in
g
19
-0
3
7
3
1
26
-0
2
in
g
so
w
thesis
root yield
weed dry weight
Fig. 3 - Root yield and weed dry weight at the sugar beet harvesting
Figure 4. Gastroidea poligoni
7
weed dry weight
(index number)
10
0
3
10
0
6
30
20
5
30
20
4
60
50
40
3
60
50
40
2
80
70
1
80
70
2
100
90
root yield (t/ha)
100
90
41
Influence of fallow land-use intensity on weed dynamics and crop yield in
southern Cameroon
M. Ngobo1a, S. Weise2 and M. McDonald1
School of Agricultural and Forest Sciences, University of Wales, Gwynedd LL57 2UW, Bangor,
UK.
2
International Institute of Tropical Agriculture – Humid Forest Ecoregional Centre, P.O. Box 2008
(Messa) Yaounde, Cameroon.
a
afpaØ4@bangor.ac.uk
1
Abstract
The influence of weeds community composition and dynamics on groundnuts intercropped with
cassava was assessed in three different short fallow management systems, in the Forest Margins
Benchmark Area of southern Cameroon (Central Africa). Fallow management intensities, indicated
through differing fallow types, consisted of: recurrent Chromolaena odorata-dominated fallows
(type I), C. odorata-dominated fallows that had been forest prior to the cropping phase (type II) and
bush fallows not dominated by C. odorata that had previously been forest (type III). Weed species
diversity, weed density and weed cover percentage were evaluated at six, 14 and 30 weeks after
planting, in 30 mixed crop fields. Soil properties were determined at the beginning and at the end of
the cropping period. Results showed that C. odorata thickets regulate the weed flora in natural short
fallow-food crop farming systems of southern Cameroon. However, C. odorata seemed to have a
detrimental effect on food crop productivity in 5-7 years old fallows. Cassava yields even appeared
to be greater in recurrent fallow lands dominated by that asteraceous weed species.
Introduction
In the humid forest zone of Cameroon, sectoral and macroeconomic policy reforms that occurred in
the late 1980s have led to a land-use intensification process. Long fallows (i.e. fallow lands of more
than five-years-old) became less and less feasible in the area. The traditional farming system has
been ‘short-circuited’. Herbaceous fallow lands dominated by one species are replacing bush
fallows. In particular, bushes of Chromolaena odorata (L.) R. M. King & H. Robinson (Asteraceae)
are gradually replacing secondary forest pioneer species. A trial was initiated in the forest zone of
southern Cameroon to determine the effect of land use intensification and the invasion of
Chromolaena odorata on weed dynamics and crop production in selected fallow classes with
different land-use history.
Materials and methods
The experiment was laid out in a randomised complete block design with 10 replicates. Study fields
included groundnuts intercropped with cassava and maize. Three fallow classes (of 5-7 years old),
corresponding to three levels of land-use intensity, were distinguished:
x C. odorata-dominated fallows that had been C. odorata-dominated fallows prior to the
cropping phase (fallow type I, indicative of high land-use intensity).
x C. odorata-dominated fallows that had been forest prior to the cropping phase (type II,
indicative of moderate land-use intensity).
42
x Bush fallows not dominated by C. odorata that had previously been forest (type III,
indicative of low management intensity).
Plots were 120 m2 divided in two parallel bands, of 3 m x 20 m each, separated by a 3-m-wide
alley. Weeds observations (counts and cover percentage estimates) were taken three times in 24
selected 0.1875-m2 quadrates per plot: at 6 Weeks After Planting, 14 WAP (at groundnut and maize
harvest) and again before cassava harvest (i.e. 30 WAP). Grain yield for groundnut and maize was
determined, and cassava tuber dry weight was assessed.
Weed data were log-transformed before analysis of variance, and means were then backtransformed for presentation. All data were analysed using the Statistical Analysis System (SAS)
software (SAS Institute, Cary, NC 27512-8000).
Results and discussion
Weed density (no.
plants. m-2)
In general, weed density and weed cover percentage increased with time in all fallow management
systems, but this increase was only significant in the recurrent C. odorata-dominated fallow fields.
In all three types of fallow, the weed flora was dominated by dicotyledons (between 78 and 90 % of
all weeds), but they differed at the species-level and varied within the cropping period (Figs. 1a and
b). Problem species like Stachytarpheta cayennensis, Cyperus rotundus and Sida rhombifolia were
distinctly less common in fallows that had recently been established from forest (Type II and III).
The weed diversity of the bush fallow (Type III) was greatest – the 5 most common species
accounting for only 33% of the weeds against 46% or more in the Chromolaena odorata fallow
types. This result is consistent with previous studies (Zapfack et al., 2000). Fallow systems
established from forest were better than recurrent C. odorata-dominated fallows in suppressing
weeds in the long term.
400
6 WAP
14 WAP
30 WAP
300
200
100
0
I
II
Fallow types
III
1
Figure 1a. Weed flora density changes over time in fallow management
systems of southern Cameroon
1
Fallow types: I=High land-use intensity, II=Moderate land-use intensity, III=Low
management intensity.
43
C. odorata density (no.
plants. m-2)
300
250
200
6 WAP
14 WAP
30 WAP
150
100
50
0
I
II
Fallow types1
III
Figure 1b. Effect of fallow management on C. odorata density changes
over time in southern Cameroon
(1Fallow types: I=High land-use intensity, II=Moderate land-use intensity, III=Low
management intensity.)
The means of groundnut grains and cassava tuber yields for each of the three fallow types are
shown in Figs. 2a and 2b. Both yields appeared to be greatest after a C. odorata-dominated fallow,
and lowest in the bush fallow fields’ type. The higher yield level observed in C. odorata-dominated
fallow systems may be due to an improved soil fertility associated with the presence of C. odorata.
Though supported by previous studies (see for example Weise, 1996; Muniappan, 1994), this
conclusion, in the case of the study area, still need to be confirmed by further investigations of soil
data collected during this experiment.
3.50
Dry weight (t.ha-1)
3.00
2.50
2.00
Groundnut grains
Cassava tuber
1.50
1.00
0.50
0.00
Ftype I
Ftype II
Ftype III
1
Fallow types
Figure 2. Effect of fallow management on crops yield in southern
cameroon
1
( Fallow types: I=High land-use intensity, II=Moderate land-use intensity, III=Low
management intensity)
44
Conclusion
In summary, as pressure on land increases, longer fallows become scarce. Although the weed
density does not appear to increase with shorter fallows, more problematic species start to become
more abundant. Grasses do not yet play a dominant role in the weed flora.
Acknowledgements
The USAID-Central African Regional Programme for Environment (CARPE) funded this research.
References
MUNIAPPAN, R. (1994). Chromolaena odorata (L.) R. M. King & Robinson in Weed
management for developing countries. Labrada, R., Caseley, J. C. and Parker, C. (eds). FAO
Plant Production and Protection Paper 120.
WEISE, S. F. (1993). Distribution and significance of Chromolaena odorata (L.) R. King & H.
Robinson across ecological zones in Cameroon in Proceedings of the Third International
Workshop on Biological Control and Management of Chromolaena odorata. Pp. 29-38.
ZAPFACK, L., WEISE, S. F., NGOBO, M., TCHAMOU, N. AND GILLISON, A. (2000).
Biodiversité et produits forestiers non ligneux de trois types de jachères du Cameroun
méridional in Floret, Ch. & Pontanier, R. (eds). La Jachère en Afrique Tropicale: Rôles,
Aménagement, Alternatives. Vol I. Actes du Séminaire International, Dakar, 13-16 Avril 1999.
Pp. 484-492.
45
Effects of crop density, spatial uniformity and weed species
on competition with spring wheat Triticum aestivum.
Jannie Maj Olsen, Lars Kristensen, Hans-Werner Griepentrog and Jacob Weiner
The Royal Veterinary and Agricultural University, Department of Ecology,
Botanical Section, Rolighedsvej 21, DK 1958 Frederiksberg, Denmark
E-mail: jao@kvl.dk
Abstract
The goal of reducing the use of herbicides in agriculture has increased interest in alternative
methods in weed management. One approach is to increase the ability of the crop to itself suppress
weeds by altering the crop density and spatial distribution. We hypothesize that (1) increasing the
crop density and (2) sowing the crop in a grid pattern instead of traditional rows can substantially
increase weed suppression. In a high density, uniformly-distributed crop population, crop plants
start competing with weed plants before they start competing with other crop plants, and the
competition between crop and weed begins before the crop loses its initial size advantage.
A field experiment was conducted to determine the effect of three densities (204, 449 and 721
plants m-2) and two spatial patterns (normal rows and a uniform grid pattern) of spring wheat
(Triticum aestivum L. cv. Leguan) on interspecific competition with six weed species with various
forms of growth (Sinapis alba, Lolium multiflorum cv. Liquattro, Papaver rhoeas, Chenopodium
album, Matricaria perforata and Stellaria media). The different weed species were sown in high
densities to obtain high weed pressures. The biomass of the target weed species and other weeds
was measured in early July.
There were strong and highly significant effects of both crop density and spatial distribution on
weed biomass in all cases. The biomass of the target weed and target weed plus naturally-occurring
weeds decreased with increasing crop density.
Overall, the total weed biomass was 30 % lower when the crop was sown in a uniform grid pattern
than crop sown in traditional rows.
The total weed biomass was reduced by 60 % for S. alba, 66 % for L. multiflorum, 42 % for P.
rhoeas, 85 % for C. album, 22 % for M. perforata and 78 % for S. media when the crop was sown
in the uniform pattern and the high density in comparison to rows at 449 m-2, which is close to
normal practice.
46
Preventive weed control in lower input farming system
V. Pilipavicius
Lithuanian University of Agriculture
Studentu g. 11, Akademija-Kaunas district, E-mail.: vpilip@nora.lzua.lt
Abstract
Weed seed rain in the crop of spring barley begins when spring barley are in steam elongation stage
and increases to the hard stage of maturity. The general number of all poured weed seed species
covers from 5.8% to 22.7% - till the medium milk stage of maturity, 26.6% - 41.8% - till late milkearly-dough stage, 48.4% - 90.6% - till dough stage from the number of all weed seeds poured on
the soil.
Harvesting spring barley in medium milk or late milk-early dough stages of maturity,
unpoured weed seeds would be taken out of the field together with yield. Therefore, harvesting
spring barley in these stages, the amount of weed seeds getting into the soil and potential weedness
of the future crop decreased.
Key words: weed seeds, weed seed rain, stages of spring barley maturity, lower input farming
system
Introduction
Growing together with agricultural plants weeds adapted to their growth and biological cycle of
development. The spreading of weed seeds in the fields is increasing by present processing
technology of cereal when late weeds have already been poured their seeds.
Herbicides are used that soil would not be polluted by new weed seeds. Although herbicides
cannot destroy all weeds, they damage them, and weeds ripen fewer amounts of seeds. However,
weeds ripen seeds in the crops that are sprinkled with herbicides and pollute soil, straws and awns
by them (Ciuberkis, 1995a, 1995b).
In recent years ecological and economic factors arouse a need and a necessity to decrease the
use of herbicides or even to refuse of them (Wacker, 1989). That is possible only using alternative
means of weedness control. It is necessary to pay attention that plants’ spreading by seeds is
characteristic not only for annual but also for perrenial weeds, as Cirsium arvense, too (Zwerger,
1996).
The quality of weedness control in today’s agriculture depends on ability to eliminate seeds,
which are still in the soil, and to limit the amount of new ones.
The place of the researches and the scheme of the trial
Preventive weed control trial in lower input farming system was carried out in 1997, 1998 and 1999
at the Research station of Lithuanian University of Agriculture. The field trial was arranged and
carried out according to the scheme, which was made on the basis of spring barley stages of
maturity by Zadoks et al. (1974).
47
The scheme. Spring barley are harvested in the stages of maturity:
1. Hard
92*,
91-92, 92
5. Early milk
71-73, 69-71, 69-71
2. Dough
87,
85,
87
6. Heading
57-59, 55,
57-59
3. Late milk-early dough 77-83, 77-83, 77-83 7. Steam elongation
39-41, 37-39, 31
4. Medium milk
75,
73-75, 73
Note. * - Decimal code for the growth stages of cereal in 1997, 1998 and 1999
Agrotechnics of spring barley cultivation
Preceding crop for spring barley was winter wheat Triticum aestivum (1997), spring barley
Hordeum vulgare (1998) and culturamaranth Amaranthus spp. (1999). In every year of the trial
double –rowed barley “Roland” were grown. Herbicides were not used in the field, as in lower
input farming system, for evaluation of alternative ways of weedness control. Soil tillage in every
year of the trial was the same.
Agrochemical characterisation of arable soil
The soil allocated for the trial is sod-gleyic light loam clay. The agrochemical characteristics of
arable soil where spring barley were grown did not vary a lot. In 1997, 1998 and 1999 arable layer
of soil was: pHKCl 7.08-7.25, humus 2.22-2.45%, active P2O5 – 245.0-251.3 mg kg-1 and active K2O
– 93.6-110.5 mg kg-1.
Establishment of weedness
Weed samples were taken at the early milk stage for general weedness establishment. There were
taken for 10 samples from every field using wire frame of 20x30cm. Air-dried weeds were divided
into species, calculated and weighed.
Establishment of weed seed rain
Dynamics of weed seed rain in spring barley crop was established according to Rabotnov’s (1960)
methodics taking into account the crop weed seed rain trials of Stancevicius & Girkute (1972),
Moss (1983) and Leguizamon & Roberts (1982). 50 troughs were laid out in each of four
replications, in chess-order, in tens. The size of one trough was 20x2x0.5 cm. The general view of
troughs is presented in Fig. 1. Weed seeds from the troughs were collected every 2, 3 or 4 days. The
collected seeds were divided into species and calculated.
Figure 1. Troughs for collecting weed seeds in spring barley crop.
48
Results
Weedness of spring barley crop
Chenopodium album, Stellaria media, Sonchus asper prevailed of annual weeds and Sonchus
arvensis from perenial ones, in spring barley crop over the period of 1997-1999. As predominated
weed species, at the first year of the trial (1997), additionally were excluded Sinapis arvensis,
Tripleurospermum inodorum and Erysimum cheiranthoides. The trial in 1997 was arranged in a
very weedy field. There were 395.3 weeds m-2 and 255.4 g m-2 of air-dried weed biomass. In 1998
the amount of weeds was more than three times less and biomass was 2.6 times less than in 1997
and reached 122.5 weeds m-2 and 97.8 g m-2 of air-dried weed biomass. In 1999 the number of
weeds was 135.0 weeds m-2 analogically as in 1998 but their air-dried biomass was more than 6
times less and covered only 18.9 g m-2 (Tab. 1.). Evaluating weedness of the crop, weeds
dependence to biological groups was established: in 1997 annual weeds covered 98.2% and
perennial - only 1.8%; in 1998 – 84.0% and 15.6% and in 1999 – 89.2% and 10.8% accordingly.
Comparing biomass of weeds, a fewer gap between annual and a perennial weed was established. It
was 97.7% and 2.3% in 1997, 70.2% and 29.8% in 1998 and 67.6% and 32.4% in 1999 accordingly.
During all three years of trial annual weeds predominated which mainly spread by seeds (Tab. 1.).
Weed seed rain in the crop of spring barley
Collected weed seeds during three years of trial belonged to 29 weed species from 12 families,
presented in table 2. In the crop of spring barley in growth stage of steam elongation (usually it
was in the second ten-day period of June), according to the data of the trial weeds of short
vegetation period Stellaria media, Poa annua and early summer weeds Chenopodium album
ripened and began to pour their seeds. Winter weeds as Capsella bursa-pastoris ripened and
poured seeds in heading growth stage of spring barley, usually it was in the third ten-day period of
June. Spring barley changing into milk stage of maturity (usually in the second ten-day period in
July) Lamium purpureum, Apera spica-venti, Atriplex patula, Veronica arvensis, Sonchus asper
and Myosotis arvensis ripened and began to pour seeds. But the beginning of ripeness and pouring
of some weed species lasts more than presented growth stages of spring barley; Chenopodium
album seeds in 1997 began to pour in steam elongation stage, in 1999 – in heading and in 1998 –
in medium milk stage of spring barley maturity. It depended on climate conditions and weedness
of crop in each year. If the crop was weedier, seeds poured more intensively and it was easier to
establish the beginning of weed seed rain. In 1997 in early milk stage of maturity 17.4%, in 1998 –
20.0%, in 1999 – 40.0% of weeds ripened seeds in the crop began to pour their seeds. In medium
milk stage of spring barley (usually at the end of the second, till the beginning of the third, ten-day
period in July) Thlaspi arvensis, Raphanus raphanistrum, Spergula arvensis, Galium aparine,
Fallopia convolvulus and Polygonum laphatifolium ripened and began to pour seeds. Spring barley
changing from milk into dough stage of maturity (usually at the end of the third ten-day period in
July), Sinapis arvensis, Sonchus arvensis, Erysimum cheiranthoides and Cirsium arvense ripened
and began to pour seeds. In spring barley late milk-early dough stage of maturity weeds ripened
seeds: in 1997 - 74%, in 1998 – 90% and in 1999 – 80% of growing and ripening seeds weed
species in the crop. In dough stage of maturity of spring barley, Avena fatua, Crepis tectorum,
Anthemis arvensis and Anthemis tinctoria ripened and began to pour seeds. At that time all species
of weeds, which poured seeds, were ripened except for in 1998 when Crepis tectorum seeds began
to pour only when spring barley reached hard stage of maturity. The data of the trial showed that
Crepis tectorum, Cirsium arvense and Sonchus arvensis ripened seeds the most late and began to
pour them (Tab. 2.).
49
Table 1. Composition, number and air-dried biomass of weed species in spring barley crop, 19971999
Weed species
1997
weeds m-2
1
Stellaria media (L.) Vill.
Poa annua L.
Annual ephemeral
Chenopodium album L.
Sinapis arvensis L.
Galeopsis tetrahit L.
Spergula arvensis L.
Galium aparine L.
Polygonum aviculare L.
Erysimum cheiranthoides L.
Galinsoga parviflora Cav.
Raphanus raphanistrum L.
Polygonum laphatifolium L.
Fallopia convolvulus (L.) A. Löve
Euphorbia helioscopia L.
Veronica arvensis L.
Amaranthus spp. L.
Chaenorrhinum minus (L.) Lange
Crepis tectorum L.
Sonchus asper (L.) Hill.
Summer annual
Medicago lupulina L.
Tripleurospermum inodorum (L.) Sch. Bip.
Thlaspi arvense L.
Viola arvensis Murray
Myosotis arvensis (L.) Hill.
Lamium purpureum L.
Capsella bursa-pastoris (L.) Medik.
Winter annual
Annual
Plantago major L.
Trifolium pratense L.
Perennial, spreading by seeds
Tussilago farfara L.
Elytrigia repens (L.) Nevski
Stellaria graminea L.
Sonchus arvensis L.
Cirsium arvensis (L.) Scop.
Mentha arvensis L.
Perennial, spreading vegetatively
Perennial
All weeds
2
37.92
7.5
45.42
29.48
147.92
0
0
2.50
0.42
62.08
0
0.42
8.33
2.08
3.75
2.5
0
0.42
3.33
16.36
279.59
1.25
34.17
4.58
3.33
1.67
1.25
17.08
63.33
388.34
2.5
1.25
3.75
0
0
0
0.31
2.92
0
3.23
6.98
395.32
Number and air-dried biomass of weeds
1998
1999
g m-2
3
17.13
0.50
17.63
131.25
69.23
0.0
0.0
0.30
0.07
6.39
0.0
0.17
0.91
0.14
0.18
0.08
0.0
0.01
0.88
8.98
218.59
0.18
10.92
0.49
0.18
0.13
0.05
1.37
13.32
249.54
0.13
0.02
0.15
0.0
0.0
0.0
0.17
5.58
0.0
5.75
5.90
255.44
weeds m-2
4
7.08
0
7.08
70.0
1.67
1.67
0.42
2.08
0
1.67
0.83
0
3.75
5.42
0.83
0
0
1.25
0
3.33
92.92
0
0
0
0.42
0
0
2.50
2.92
102.92
0.42
0
0.42
1.25
0
0
15.84
2.08
0
19.17
19.59
122.51
g m-2
5
3.79
0
3.79
53.96
1.05
0.29
0.25
1.08
0.0
0.19
0.17
0.0
0.56
1.45
0.20
0.0
0.0
0.04
0.0
5.21
64.45
0.0
0.0
0.0
0.04
0.0
0.0
0.44
0.48
68.72
0.81
0.0
0.81
0.12
0.0
0.0
24.77
3.43
0.0
28.32
29.13
97.85
weeds m-2
6
9.17
5.0
14.17
66.25
0
0
0
0
0
1.25
0
0
0.42
0
0.83
4.17
10.83
2.50
0
0.87
87.12
0
2.92
0.42
1.67
0
0.83
13.33
19.17
120.46
2.92
0
2.92
0.0
2.5
0.42
6.21
0.83
1.67
11.63
14.55
135.01
g m-2
7
2.73
0.10
2.83
5.67
0.0
0.0
0.0
0.0
0.0
0.08
0.0
0.0
0.01
0.0
0.05
0.09
0.14
1.57
0.0
0.44
8.05
0.0
0.22
0.08
0.05
0.0
0.18
1.40
1.93
12.81
0.06
0.0
0.06
0.0
2.3
0.01
3.14
0.25
0.28
6.07
6.13
18.94
50
Table 2. Weed species pouring seeds in the crop of spring barley, 1997-1999
Families
Species
Boraginaceae Juss.
Chenopodiaceae Less.
Myosotis arvensis (L.) Hill.
Atriplex patula L.
Capsella bursa-pastoris L.
Raphanus raphanistrum L.
Sinapis arvensis L.
Thlaspi arvense L.
Erysimum cheiranthoides L.
Cirsium arvense (L.) Scop.
Tripleurospermum inodora (L.) Sch.
Cruciferae B. Juss.
Compositae Giseke
Caryophyllaceae Juss.
Sonchus arvensis L.
Sonchus asper (L.) Hill.
Crepis tectorum L.
Anthemis arvensis L.
Anthemis tinctoria L.
Stellaria media (L.) Vill.
Spergula arvensis L.
The beginning of weed seed rain
1997
1998
1999
M.m.
N.
M.e.
M.m.
M.m.
M.e.
S.e.
M.e.
He.
M.m.
M.m.
He.
M.m.
M.l.-D.e.
N.
M.l.-D.e.
M.l.-D.e.
M.l.-D.e.
M.m.
N.
M.m.
M.l.-D.e.
D.
N.
D.
M.l.-D.e.
D.
D.
D.
M.l.-D.e.
D.
D.
D.
S.e.
N.
N.
M.l.-D.e.
M.m.
H.
N.
N.
M.e.
M.l.-D.e.
D.
D.
M.e.
N.
N.
N.
He.
N.
N.
M.e.
N.
N.
S.e.
D.
M.m.
M.m.
D.
M.l.-D.e.
M.m.
N.
N.
M.m.
M.e.
M.m.
N.
M.m.
M.l.-D.e.
N.
N.
M.l.-D.e.
M.e.
M.l.-D.e.
M.m.
N.
N.
N.
N.
M.m.
M.m.
N.
N.
N.
M.m.
N.
Euphorbiaceae J. St. Hill.
Labiatae Juss.
Poaceae Barnhart
Polygonaceae Lindl.
Rubiaceae Juss.
Scrophulariaceae Juss.
Violaceae Juss.
Euphorbia helioscopia L.
Lamium purpureum L.
Apera spica-venti L.
Avena fatua L.
Poa annua L.
Fallopia convolvulus L.
Polygonum lapathifolium L.
Polygonum aviculare L.
Rumex crispus L.
Galium aparine L.
Veronica arvensis L.
Viola arvensis Murr.
Note. Growth stages of spring barley: S.e. – steam elongation, He. – heading, M.e. – early milk,
M.m. – medium milk, M.l.-D.e. – late milk-early dough, D. – dough, H. – hard, N. – weed seed
rain was not established.
When spring barley was ripening, weed seed rain was more intensive. During the first ten days
from the beginning of weed seed rain in 1997 – 0.2% of seeds poured in the field, in 1998 – 0.3%,
in 1999 – 7.2% accordingly; and at the end of spring barley vegetation in 1997 – 27.9%, in 1998 –
62.7% and in 1999 – 44.5% of all amount of poured seeds (Fig. 2.).
350
51
weed seeds m-2
1997
1998
1999
300
250
200
150
100
50
`0
6,
1
`0 2
6,
1
`0 5
6,
1
`0 8
6,
2
`0 1
6,
2
`0 4
6,
2
`0 7
6,
3
`0 0
7,
0
`0 3
7,
0
`0 6
7,
0
`0 9
7,
1
`0 2
7,
1
`0 5
7,
1
`0 8
7,
2
`0 1
7,
2
`0 4
7,
2
`0 7
7,
3
`0 0
8,
0
`0 2
8,
0
`0 5
8,
0
`0 8
8,
1
`0 1
8,
1
`0 4
8,
17
0
date
Figure 2. Dynamics of weed seed rain in spring barley crop, seeds m-2 every twenty-four hours,
1997-1999
The amount of all poured weed seeds was different. In 1997 the biggest amount of seeds was
found of Stellaria media (1260 seeds), Sonchus asper (1173 seeds), Sinapis arvensis L. (496
seeds), Capsella bursa-pastoris L. (457 seeds) and Chenopodium album (289 seeds). It made 81%
of all poured weed seeds in 1997. In 1998 seeds of Chenopodium album, Stellaria media and
Sonchus arvensis predominated. 1484, 802 and 133 seeds poured accordingly and they made 88%
of all poured weed seeds. In 1999 the biggest amount of Chenopodium album (519 seeds),
Stellaria media (157 seeds) and Capsella bursa-pastoris (52 seeds) seeds was found; they made
89% of all poured weed seeds (Tab. 3.). In 1997 the general amount of all poured weed seeds
made only 4.6% when spring barley were changing into milk stage of maturity. 16.8% of seeds
poured till medium milk stage of maturity, 28.4% - till late milk-early dough stage and 85.2% - till
dough stage of maturity. In 1998 the general amount of all poured weed seeds made 1.7%, 5.8%,
26.6% and 48.4% and in 1999 – 7.3%, 22.7%, 41.8% and 90.6% accordingly.
Analogical data were got analysing weed seed rain of separate species. About 70% of weed
species which pour seeds till medium milk stage of spring barley maturity poured less than 20% of
all their seeds pouring during vegetation, till late milk-early dough stage of maturity - about 65%
of weeds species poured till 40% of their seeds and till dough stage – only 5% of weeds species
poured less than 40% and even 37% of weed species poured more than 80% of all their seeds
poured till hard stage of spring barley maturity.
Harvesting spring barley in milk or late milk-early dough stage of spring barley maturity,
unpoured weed seeds are taken from the field together with yield. So, it helps to decrease the
amount of weed seeds and potential weedness of the crop.
Myosotis arvensis
Atriplex patula
Chenopodium album
Raphanus raphanistrum
Sinapis arvensis
Thlaspi arvense
Erysimum cheiranthoides
Cirsium arvense
Tripleurospermum inodora
Anthemis arvensis
Anthemis tinctoria
Sonchus arvensis
Sonchus asper
Crepis tectorum
Stellaria media
Lamium purpureum
Fallopia convolvulus
Polygonum lapathifolium
Polygonum aviculare
Poa annua
Rumex crispus
Galium aparine
Veronica arvensis
All species
LSD05
1
Weed species
3
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
10
0
0
0
0
3
0
0
0
16**
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
4
0
0
0
0
2
0
0
0
8**
Heading
Steam
elongation
2
Table 3. Weed seed rain in the crop of spring barley, 1997-1999
Stages of spring barley maturity
Early milk
Medium
Late milkmilk
early dough
4
5
6
1997
0
6
14
0
1
1
5
23
55
63
165
186
0
1
9
0
0
12
0
5
22
0
0
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
79
0
0
0
119
524
846
4
5
6
0
0
0
0
4
6
0
1
1
16
23
29
0
0
0
0
0
2
0
6
18
207**
764**
1289**
33
2
254
421
81
368
68
122
11
59
1
10
14
1011
50
1228
8
2
34
1
29
9
3
52
3871
7
Dough
43
3
289
457
96
496
78
149
45
167
1
10
22
1173
66
1260
8
3
41
1
29
33
3
70
4543
707.0
8
Hard
52
1
Atriplex patula
Chenopodium album
Avena fatua
Apera spica-venti
Raphanus raphanistrum
Sinapis arvensis
Erysimum cheiranthoides
Cirsium arvense
Sonchus arvensis
Sonchus asper
Crepis tectorum
Stellaria media
Spergula arvensis
Lamium purpureum
Galium aparine
Veronica arvensis
Viola arvensis
All species
LSD05
LSD01
LSD01
Table 3. (Continued)
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0**
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0**
4
1998
0
12
0
8
5
0
0
0
0
0
0
0
21
0
0
0
0
0
1
0
47**
6
36
1
30
5
0
0
0
0
0
4
0
73
0
1
4
0
0
1
0
161**
5
6
265
1
53
5
3
1
0
1
1
7
0
363
3
1
13
2
5
1
0
731**
6
6
526
1
65
5
5
3
29
2
31
18
0
592
3
1
22
6
13
2
1
1331**
7
8
1484
6
85
5
6
13
93
2
133
28
1
802
3
1
32
30
18
2
1
2753
417.7
572.1
8
968.4
53
1
3
0
0
2
10
0
0
0
0
0
0
0
0
0
0
0
12**
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0**
4
1999
1
2
12
29
0
0
0
0
0
3
12
0
0
0
0
60**
2
2
45
44
0
4
0
0
0
3
74
1
1
1
9
186**
5
Note. LSD05 and LSD01 calculated essential differences only for seed sum of all weed species.
Myosotis arvensis
Atriplex patula
Chenopodium album
Sinapis arvensis
Thlaspi arvense
Cirsium arvense
Tripleurospermum inodora
Sonchus arvensis
Sonchus asper
Stellaria media
Euphorbia helioscopia
Veronica arvensis
All species
LSD05
LSD01
Table 3 (Continued)
2
6
122
45
1
4
0
0
0
3
141
1
2
5
10
343**
6
2
16
459
51
1
4
9
4
9
3
158
1
5
8
15
744*
7
2
19
519
52
1
4
11
5
18
3
158
1
6
8
15
821
71.5
97.9
8
54
55
Discussion
The data of the field trial proved that weeds ripened regularly. It was established that to 4543 seeds
m-2 poured till harvesting of spring barley. Different number of weed seeds depended on crop
density, agrotechnics, meteorological conditions and the characteristic of soil (Petraitis et al., 1993).
Weed seed rain in spring barley crop began in steam elongation stage and gradually increased
till hard stage of maturity. From 6% to 23% of all poured weed seeds poured till medium milk stage
and from 27% to 42% - till late milk-early dough stage of maturity. Weed seeds which were left in
the crop were taken from the field together with the biomass of spring barley and did not pollute the
soil: 77% - 94% till medium milk stage and 58% - 73% - till late milk-early dough stage of
maturity. Moreover, most of all poured weed seeds, which were in silage (Grigas 1980, 1981;
Grigas & Smulkiene, 1989a; Blackshaw & Rode, 1991), in manure (Grigas 1980, 1981; Sarapatka
et al., 1993), in sewage (Grigas & Smulkiene, 1989b) and in compost (Tereshchuk, 1995), or going
through alimentary canal of cattles’ (Grigas, 1987; Blackshaw & Rode, 1991), lost their
germinating power and did not pollute the crop.
The presented way of spring barley management fully satisfy the criteria of ecological farms
and are perspective in lower input farming system.
Acknowledgements
We thank Mrs. Vilma Pilipaviciene for article translation from Lithuanian into English.
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treatment on weed seed viability. Biological Agriculture and Horticulture 10, 1-8.
14. STANCEVICIUS A & GIRKUTE A (1972) Piktzoliu seklu byrejimo dinamika javu paseliuose.
LZUA mokslo darbai Zemes ukio intensyvinimas 28, 25 - 34.
15. TERESHCHUK V (1995) Sources of weed infestation of agricultural land and the problems of
weed control. In: Proceedings 9th EWRS Symposium – Challenges for Weed Science in a
Changing Europe, Budapest, Hungary, 135-141.
16. WACKER P (1989) Bekampfung von Unkrautern bei der Getreideernte. Landtechnik 6, 215-219.
17. ZADOKS JC, CHANG TT & KONZAK CF (1974) A decimal code for the growth stages of cereals.
Weed Research 14, 415 – 421.
18. ZWERGER P (1996) Zur Samenproduktion der Acker-Kratzdistel (Cirsium arvense (L.) Scop.).
Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz Sonderheft XV, 91–98.
57
The effects of cultural practices on crop and weed growth in organic spring oats
B. R. Taylor and D. Younie
SAC, Craibstone Estate, Bucksburn, Aberdeen AB21 9YA, UK
Abstract
Trials in 1993 and 1994 on organic farms near Aberdeen and Elgin, UK, evaluated a range of
methods for controlling weeds in spring oats (Avena sativa). These included cultivars of different
heights, seed rates, row spacings, undersowing with a grass/clover mixture and mechanical tined
weeding. Crop and weed biomass were measured during the growing season, important weed
species identified and grain yield assessed. Cereal varieties, despite being chosen for their different
heights and competitive abilities, had no significant effect on weed biomass during the growing
season. Weed biomass was reduced where the crop was sown at high seed rates and at narrrow row
spacings. Mechanical weeding resulted in a reduction in weed biomass. The amount of crop present
at a given time appeared to have the most influence on weed biomass at Elgin , whereas plant
distribution had greater influence at Aberdeen. Grain yields were low in 1993 at both sites; there
were increases in grain yield from the use of narrow rows and, at one site, from higher seed rates
and undersowing with a grass/clover mixture. In 1994, yields were higher and there were significant
increases from the use of higher seed rates but less effect of using close row spacing. There was no
increase in grain yield from mechanical weeding in either year.
Introduction
Weeds are the most common problem faced by organic cereal farmers (Taylor et al., 2001). Where
no herbicides are used, weeds may comprise more than 50% of the total above ground biomass in
organic cereal fields with yield losses of 20% being reported (Rasmussen & Ascard, 1995).
The aim of weed management strategies in organic farming systems is not to eliminate weeds
completely but to maintain them at a manageable level by indirect measures (rotation design, variety
choice and sowing date) so that direct control measures can succeed in preventing crop losses
(Taylor et al., 2001). Methods of weed control for organic farming systems are described by Davies
& Welsh (2002), and as well as structural methods, these include manipulation of crop growth and
cultivations before and after crop emergence. Harrow comb or spring-tine weeding is the most
frequent direct method used (Bulson et al., 1996) and is most effective when done in the standing
crop, after weed emergence but before cereal stem extension (Samuel & Guest, 1990).
Easson et al. (1995) found crop competitiveness to be important in weed suppression, even where
low rates of herbicide were used in conventional cereals. Competitiveness is increased where the
crop is tall, where plant establishment is rapid and where the crop quickly forms a complete ground
cover, particularly against late-emerging weeds (Lolz et al., 1995). Richards & Whytock (1993)
suggested that the visual assessment of 'early ground cover' at mid to late tillering and 'canopy
density' between the flag leaf stage and ear emergence were useful indicators of the competitiveness
of cereal varieties with weeds. Bertholdsson & Jonsson (1994) found that the fresh weight of plants
grown in water for 14 days could be related to rapid early development and competitiveness in oats.
58
Mailland-Rosset (2000) showed that for barley, but not for oats, there are several plant charcteristics
which affect the ability of the crop to compete for light.
Trials to manipulate the competitiveness of organically grown spring oats were sown at Tulloch,
Craibstone Estate near Aberdeen, and at Woodside, Aldroughty Estate near Elgin, in Scotland.
Tulloch is a mixed upland farm (155 m above sea level; annual rainfall 850 mm), marginal for crop
production and has a sandy loam soil of the Countesswells Association with imperfect drainage.
Woodside is a lowland arable farm (25 m above sea level; annual rainfall 730 mm) with a freely
drained sandy loam soil of the Elgin Association. Trials followed grass/clover leys.
Treatments for the spring oats in 1993 were: 2 varieties of contrasting straw heights (Dula and
Matra); 2 seedrates (150 and 300 kg ha-1); 2 row spacings (9 and 18 cm); 3 cultural weed control
methods (none, undersowing with a grass/clover seeds mixture in spring, and mechanical weeding
by Lely weeder carried out once through the crop on two separate occasions). The 24 treatment
combinations were replicated twice at each location in randomised complete blocks.
Treatments for the spring oats in 1994 were: 3 seedrates (150, 225, and 300 kg ha-1); 3 row spacings
(9, 13.5, and 18 cm); 2 cultural weed control methods (none, and mechanical weeding by Temple
Harrow Comb carried out once through the crop on two separate occasions). The 18 treatment
combinations were replicated three times at each location in randomised complete blocks.
The cereals were sown in plots of 20 m x 3.1 m using an Accord pneumatic drill. The grass/clover
mixture was sown at the same time as the oats in 1993 using a Sisis roller feed drill. Dates of
sowing and first and second mechanical weedings were 15 April, 26 May and 9 June respectively at
Tulloch in 1993, 25 March, 25 May and 28 May at Woodside in 1993, 28 March, 12 May and 23
May for Tulloch in 1994, and 1 April, 11 May and 19 May for Woodside in 1994. The first
mechanical weedings approximated to Zadok's growth stage 13-14 and the second to mid-tillering.
Sequential sampling of above ground vegetation was carried out by cutting three 0.27 m2 quadrats at
ground level in each plot, initially at 2 week intervals but later at 4 week intervals, starting in mid
May; dates of sampling are shown with the results. Trials were harvested by plot combine on 19
October 1993 and 5 September 1994 at Tulloch and 21 September 1993 and 31 August 1994 at
Woodside, samples being taken for oven determination of grain dry matter. Grain yields were
corrected to 85% dry matter content.
Results
In 1993 and 1994 chickweed (Stellaria media) and mayweeds (Matricaria spp.) contributed the
majority of the weed biomass at Tulloch. At Woodside wild oats (Avena fatua), corn marigold
(Chrysanthemum segetum) and chickweed dominated in 1993, and chickweed, mayweed spp.,
polygonums (Polygonum spp.) and field pansy (Viola arvensis) in 1994.
0.6
(a)
150 kg ha-1
300 kg ha-1
0.5
0.4
0.3
0.2
0.1
0.0
May
Jun
Jul
Aug
Sep
3.0
Biomass (t ha-1)
Biomass (t ha-1)
0.7
59
Oct
2.5
(b)
2.0
1.5
1.0
-1
150 kg ha
-1
300 kg ha
0.5
0.0
May
Jun
Jul
Date
1.2
1.0
0.8
-1
150 kg ha
-1
225 kg ha
-1
300 kg ha
(c)
0.6
0.4
0.2
0.0
May
Jun
Jul
Date
Sep
Oct
Date
Biomass (t ha-1)
Biomass (t ha-1)
1.4
Aug
Aug
Sep
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
May
-1
150 kg ha
-1
225 kg ha
-1
300 kg ha
Jun
(d)
Jul
Aug
Sep
Date
Figure 1. Effect of crop seed rate on weed biomass at (a) Tulloch in 1993, (b) Woodside in 1993, (c)
Tulloch in 1994 and (d) Woodside in 1994.
Weed biomass decreased after July at Tulloch but reached a constant level at Woodside. Weed
infestation was severe at Woodside in 1993 when May rainfall was 50% above avarage.Yields of
total weed biomass at sequential sampling dates are presented in Figures 1 to 3 for Tulloch and
Woodside. For analyses of variance biomass data were transformed to log10. Oat variety had little
effect on crop or weed biomass in 1993 and variety data are meaned.
Effect on weed biomass
In the four trials, higher crop seed rate gave significant reductions in weed biomass at all but three
samplings (Tulloch 29 Sept. 93 and Woodside 20 May 93 and 6 Sept. 93). In 1994 weed growth in
the 225 and 300 kg ha-1 crop seedrate treatments was less than in the 150 kg ha-1 treatment (Fig. 1).
Crop row spacing had a less consistent effect on weed biomass than seed rate, but nevertheless was
significant at Tulloch on 17 June 93, 12 July 93, 2 Aug. 93, 23 May 94, 9 June 94 and 19 Aug 94,
and at Woodside on 31 May 93, 15 June 93, 6 Sept. 93 and 20 May 94 (Fig. 2). The effects of
cultural/mechanical weed control were significant at all dates except 2 Aug. 93 at Tulloch and 15
June 93, 5 July 93, 20 May 94, 20 June 94 and 23 Aug. 94 at Woodside (Fig. 3). Harrowing reduced
weed biomass at both sites although at Woodside the effect was not apparent by the time of the final
sampling. Undersowing in 1993 resulted in lower weed biomass than harrowing at the late
samplings. Treatments did not show consistent interactions for weed biomass at either site.
0.6
3.5
9cm Rows
18cm Rows
(a)
Biomass (t ha-1)
Biomass (t ha-1)
0.7
60
0.5
0.4
0.3
0.2
0.1
0.0
May
Jun
Jul
Aug
Sep
Oct
3.0
(b)
2.5
2.0
1.5
1.0
9cm Rows
18cm Rows
0.5
0.0
May
Jun
Date
1.2
1.0
0.7
9cm Rows
13.5cm Rows
18cm Rows
(c)
0.8
0.6
0.4
0.2
0.0
May
Jun
Jul
Date
Aug
Sep
Oct
Date
Biomass (t ha-1)
Biomass (t ha-1)
1.4
Jul
Aug
Sep
0.6
9cm Rows
13.5cm Rows
18cm Rows
(d)
0.5
0.4
0.3
0.2
0.1
0.0
May
Jun
Jul
Aug
Sep
Date
Figure 2. Effect of crop row spacing on weed biomass at (a) Tulloch in 1993, (b) Woodside in 1993,
(c) Tulloch in 1994 and (d) Woodside in 1994.
Effects on crop biomass
Increased seedrate gave significantly more crop biomass in all trials at most sampling dates. Row
spacing and mechanical weed control had relatively small effects on crop biomass, neither having
significant effects at Tulloch in 1993. There were no consistent patterns of significance for
interactions for crop biomass, although cultural weed control and seedrate showed significant
interactions at Woodside; mechanical weeding reduced crop dry matter in the 150 kg ha-1 treatment
and increased it in the 300 kg ha-1 treatment in 1993, with the opposite effect in 1994.
0.5
0.4
0.3
0.2
None
Undersown
Harrow
0.1
0.0
May
3.5
(a)
Biomass (t ha-1)
Biomass (t ha-1)
0.6
61
Jun
Jul
Aug
Sep
Oct
3.0
(b)
2.5
2.0
1.5
None
Undersown
Harrow
1.0
0.5
0.0
May
Jun
Date
Biomass (t ha-1)
Biomass (t ha-1)
0.6
0.4
0.2
0.0
Jun
0.5
(c)
None
Harrow
0.8
May
Jul
Date
Aug
Sep
Oct
Date
1.2
1.0
Jul
Aug
Sep
(d)
0.4
0.3
0.2
None
Harrow
0.1
0.0
May
Jun
Jul
Aug
Sep
Date
Figure 3. Effect of cultural control methods on weed biomass at (a) Tulloch in 1993, (b) Woodside
in 1993, (c) Tulloch in 1994 and (d) Woodside in 1994.
Weed and crop growth interactions
The relationships between weed and crop growth were examined by regression. Weed biomass was
modelled by fitting crop biomass and adding the effects of seedrate, rowspace, cultural weed control
and the interactions of these treatments with each other and with crop biomass. Once again the few
interactions that were significant showed no consistent pattern. The significance levels of fitted
regressions for crop biomass and the main effects of treatments are given in Table 1. At Tulloch in
1993 the only significant regression of weed on crop biomass was positive and occurred late in the
season. At Woodside in 1993 a positive regression of weed on crop biomass at the start of the season
was followed by significant negative regressions at all other dates. In 1994 significant negative
regressions occurred at both sites. In 1993 seedrate, row spacing and cultural weed control affected
weed biomass independently of crop biomass at Tulloch, whereas there appeared to be few treatment
effects at Woodside. In 1994 all treatments had significant effects on weed biomass at Tulloch
whereas only seedrate and cultural weed control influenced weed biomass at Woodside.
62
Table 1. Significance of crop biomass and main treatment effects on weed biomass at sequential
sampling dates in regression analyses.
Trial
Sample date
Regression of log
weed on log crop
+ seed rate
+ row space
+cultural
control
Tulloch 93
31 May
17 June
12 Jul
2 Aug
29 Sep
-0.13 ns
0.07 ns
-0.43 ns
0.65 *
0.66 ns
**
*
***
***
ns
ns
**
**
**
ns
*
*
**
ns
*
Woodside 93
20 May
31 May
15 Jun
5 Jul
6 Sep
0.19 ***
-0.54 **
-0.68 ***
-1.00 ***
-1.25 ***
***
ns
ns
ns
ns
ns
ns
ns
ns
ns
***
ns
*
ns
ns
Tulloch 94
26 May
9 Jun
24 Jun
21 Jul
19 Aug
-1.72 ***
-0.37 ns
-0.98 ns
-1.28 *
0.75 ns
ns
**
ns
**
***
ns
**
ns
ns
*
***
**
**
***
**
Woodside 94
23 May
6 Jun
20 Jun
18 Jul
23 Aug
-0.26 ns
-1.61 ***
-0.62 *
-2.48 ***
-0.91 ns
***
ns
***
***
***
ns
ns
ns
ns
*
ns
*
*
**
ns
ns: not significant, significant at *P=0.05, **P=0.01, ***P=0.001
Effects on grain yields
Table 2. Grain yield (t ha-1 at 85% d.m.): main effects of row spacing in 1993 and 1994.
9
Tulloch 1993
Woodside 1993
Tulloch 1994
Woodside 1994
3.17
3.09
5.39
5.84
Row space (cm)
13.5
18
5.67
5.86
2.87
2.58
5.24
5.77
SED+
0.065
0.131
0.126
0.111
Grain yields were higher in 1994 than 1993. The yields of the two varieties in 1993 were not
significantly different, although the taller Dula yielded more than Matra on narrow rows at Tulloch,
the interaction being significant at 10%. The 18 cm rows gave the lowest yields in all trials and row
width differences were significant at Woodside in 1993 and Tulloch in 1994 where the intermediate
13.5 cm rows gave the highest yields (Table 2). The high seed rate gave a significant yield increase
at Woodside in 1993 (Table 3) and in 1994 grain yields were increased by increasing seedrate above
150 kg/ha at both sites. Mechanical weeding reduced mean grain yield significantly only at Tulloch
63
in 1993 but there were greater reductions in grain yield resulting from harrowing the low seed rate
treatments than the high seed rate treatments in 1993 (Table 3).
Table 3. Grain yield (t ha-1 at 85% d.m.): interactions of seedrate and cultural weed control methods
in 1993 and 1994.
Cultural weed control
None U'sow Mech
Seed rate
(kg ha-1)
Tulloch 1993
150
3.20
3.18
2.65
300
3.05
3.10
2.94
Mean
3.12
3.14
2.80
SED+ a0.112 b0.079 c0.065*
Mean
3.01
3.03
Wooside 1993
150
2.45
3.08
2.36
300
3.05
2.96
3.12
Mean
2.75
3.02
2.74
SED+ a0.227 b0.160 c0.131*
2.63
3.04
Tulloch 1994
150
5.27
225
5.45
300
5.65
Mean
5.46
SED+ a0.178 b0.103
5.03
5.76
5.42
5.40
c
0.126*
5.15
5.61
5.54
Woodside 1994
150
5.65
225
5.78
300
6.09
Mean
5.84
SED+ a0.157 b0.091
5.65
5.94
5.83
5.81
c
0.111*
5.65
5.86
5.96
*SEDs for comparisons awithin table, bundersowing/harrowing means, cseed rate means
Weed growth and grain yield
To determine whether weed growth per se had affected grain yields, grain yields were regressed on
weed biomass (untransformed data) at the different sampling dates, treatment effects having first
been removed (Table 4). Although weeds had some negative effects on grain yield, only at
Woodside in 1993, when weed biomass reached nearly 3 t ha-1, were there significant yield
reductions from weed infestation.
64
Table 4. Effects weed biomass (t ha-1 d.m.) at different dates on grain yields (t ha-1 at 85% d.m.).
Trial
Tulloch 1993
Sample date
31 May
17 June
12 Jul
2 Aug
29 Sep
Regression
+4.59 ns
-0.04 ns
+0.44 ns
+0.08 ns
+0.21 ns
Woodside 1993
20 May
31 May
15 Jun
5 Jul
6 Sep
-0.28 ns
-1.95 ns
-1.60 **
-0.71 ***
-0.36 **
Tulloch 1994
26 May
9 Jun
24 Jun
21 Jul
19 Aug
-2.93
+0.21
-0.26
-0.26
-0.34
ns
ns
ns
ns
ns
Woodside 1994
23 May
6 Jun
20 Jun
18 Jul
23 Aug
-1.69
-0.25
-0.12
-0.46
-0.13
ns
ns
ns
ns
ns
Discussion
Organic growers control weeds to maximise yields and minimise weed seed returns to the soil
(Rasmussen et al., 2000). In the present trials the effects of crop growth on weed development were
quantified during the growing season but weed seedbanks were not measured.
Control methods tested here included variety selection, sowing methods and cultivation. The two oat
varieties, though chosen for their differences in straw length (SAC, 1992), did not differ greatly in
growth or grain yield and gave no indication that varieties having a tall final straw length are more
suppressive of weeds than those with a shorter straw. Davies & Welsh (2002) suggest that long
straw is not the only requirement for weed suppression and that in wheat good overall shading
ability is more important. Bertholdsson & Jonsson (1994) found that in oats plant fresh weight may
indicate ability to compete with weeds. However, Mailland-Rosset (2000), working near Aberdeen,
found that light penetration to ground level in oat varieties between stem elongation and ear
emergence was not correlated with plant height or biomass, as it was in barley. Because oats are
more vigorous than wheat or barley, weed suppression appears less affected by height differences.
Competition between crop and weeds is important for weed suppression. In practice weed and crop
biomass may be correlated (Pearce & Gilliver, 1978) since environmental conditions which favour
growth in the one may also favour growth in the other, giving a positive correlation, or the
exploitation of resources by one may deprive the other, giving a negative correlation. On the other
65
hand, Rasmussen & Ascard (1995) have suggested that where conditions favour crop growth, for
example in situations of high soil fertility, the crop may be better able to compete effectively with
weeds than in less favourable conditions. In this paper such correlations have not been taken into
account. A significant positive regression occurred on two occasions and may have been a
consequence of favourable conditions at particular stages of development when weed and crop were
not interfering with each other.
Negative regressions indicating competition were more often significant at Woodside than at
Tulloch. In 1993, crop growth rates were roughly similar at both sites, but the weed species at
Woodside were particularly aggressive and weed biomass was greater than at Tulloch. In 1994
weed biomass was less at Woodside than at Tulloch, but crop growth was more rapid at Woodside.
Competition appears to have followed the rapid development of one component of the association.
At Tulloch there were indications that row spacing and seedrate acted independently of crop biomass
on weed biomass. This suggests that plant distribution was important, presumably through a larger
number of smaller plants at the higher seedrate or a 'squarer' arrangement of plants more widely
spaced in closer rows giving more uniform ground cover. Where growth of at least one component
was rapid, as at Woodside, the advantage of uniform crop plant distribution would be quickly lost as
crop or weed spread rapidly.
Mechanical weeding gave reductions in weed biomass, the effect being most apparent some time
after weeding had occurred, presumably because damaged weeds did not recover. In 1994 there was
some indication of increases in crop biomass as a result of mechanical weeding which may have
been a consequence of less weed competition. Grain yields were unaffected by mechanical weeding,
except at Tulloch in 1993 when they were reduced. This latter effect agrees with results from by
Bulson et al. (1996) in which grain yields were not increased by spring tine weeding, attributed to
reductions in plant density and generally poor levels of weed control.
Undersown grass and clover compete with weeds and in these trials weed biomass was reduced as a
result of undersowing. Undersowing did not reduce crop biomass and or grain yields and should be
regarded as a useful method of weed control, as well as for establishing grass/clover leys and adding
N to the system (Younie, 2001).
The trials demonstrate that measures taken to control weeds do not necessarily result in increased
grain yields unless weed competition is severe as at Woodside in 1993 where weed biomass
approached 3 t ha-1. At Tulloch and Woodside in 1994 weed growth was less than this and yields
responded to seed rates only up to 225 kg ha-1; seed rates above this had only marginal effects on
weed growth.
Although a number of practices were effective in reducing weed growth, weeds had a relatively
small effect on final grain yield in these trials. Nonetheless, organic growers are well aware of the
need to minimise weed growth and weed seed production in order to avoid future problems.
Acknowledgements
The authors acknowledge the major contributions to the field work of these trials by John Wilson,
Michael Coutts and Carey Dye, to the statistical analysis by Mike Franklin and to the presentation
of data by Robin Walker. The trials were funded by the Scottish Executive Environment and Rural
Affairs Department.
66
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Integrated farming Systems (eds DM Glen, MP Greaves & HM Anderson), 49-67, John Wiley
and Sons, Chichester, UK.
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Biology 34, 345-354.
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SAMUEL AM & GUEST SJ (1990) Weed studies in organic and conventional cereals. In: Crop
Protection in Organic and Low Input Agriculture (ed R Unwin), British Crop Protection
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67
Effect of crop competition and cultural practices on the growth
of Sonchus arvensis
P. Vanhala1), T. Lötjönen2) & J. Salonen1)
MTT Agrifood Research Finland, Plant Protection, FIN-31600 Jokioinen
E-mail petri.vanhala@mtt.fi
2)
MTT Agrifood Research Finland, Agricultural Engineering, FIN-03400 Vihti
1)
Sonchus arvensis L. (perennial sowthistle) is an increasing problem in Finland, particularly in
organic farming. Controlling S. arvensis with non-chemical methods is not an easy task. However,
crop competition (Zollinger & Kells 1991) and cultural practices like mowing (Håkansson 1969),
hoeing and fallowing (Håkansson 1969) provide some possibilities for S. arvensis management.
As a part of a larger research project focusing on perennial weeds S. arvensis, Cirsium arvense
(L.) Scop. and Elymus repens (L.) Gould., a three-year field experiment was established in 2001 at
Vihti, southern Finland, in order to study the biology and control of S. arvensis.
The experiment was placed in a clay soil (containing 6–12% organic matter) field under
organic production and heavy infestation of S. arvensis. The experimental design was randomized
blocks with five replicates. The treatments consisted of various crop plants and cultural practices
(Table 1). All crops were sown on 16 May 2001.
Table 1. Experiment protocol for the first year of the 3-year field trial.
Crop
Weed control treatments
Fiber hemp
None
Barley
None
Barley
Hoeing
Barley + undersown timothy & clover None
Timothy & clover (sown in spring)
Mowing twice during summer
Fallow
Power harrowing once + harrowing
several times during summer
The development of crop and weed plants was observed weekly (results not presented here).
Prior to harvesting of barley, on 20 August 2001, plant samples from two 0.5 m × 0.5 m quadrats
were cut at the soil surface. The growth stage (mainly according to Meier 1997) and the height of
each S. arvensis shoot were assessed. Also the total dry mass of S. arvensis per sample area was
assessed.
The beginning of the growing season 2001 was cool and rainy but turned to warm and dry in
July-August.
S. arvensis was most abundant in fiber hemp and timothy + red clover (Fig. 1). Spring-sown
timothy and clover remained short, and also the early growth of fiber hemp was slower than that of
68
barley. Later on, after mid-July, hemp was the tallest crop and had taller S. arvensis shoots than the
other crops.
In all crops, the majority of S. arvensis infestation even at the harvest time consisted of small
plants with 1–6 leaves, thus being at the compensation point (Håkansson 1969) or smaller. The
highest percentage (6%) of ripening S. arvensis seeds was in hemp.
In barley, hoeing reduced the number and mass of S. arvensis compared to other barley plots.
In timothy+red clover, cutting kept the S. arvensis plants short, mostly below 40 cm, and delayed
flowering. Fallow, cultivated six times during the summer when S. arvensis reached compensation
point, produced the least amount of S. arvensis plants. S. arvensis produced the highest dry mass in
hemp and lowest in fallow (Fig 2).
The S. arvensis infestation may be restrained with mowing or hoeing, but the effect of these
methods is not equal to fallowing. Crops growing fast in early season, e.g. barley, reduce S.
arvensis growth more than slow-growing crops.
The long-term effects of different treatments will be assessed in the next two summers.
Distribution of S. arvensis height
Growth stages of S. arvensis
200
200
120- cm
80-99 cm
100
60-79 cm
40-59 cm
50
20-39 cm
150
ripening
fruit
flowering
inflorescence
13- leaves
7-12 leaves
1-6 leaves
-2
100-119 cm
plants m
plants m -2
150
100
50
1-19 cm
0
Fa
llo
w
&c
lov
er
Ti
m
ot
hy
tim
&c
lov
ho
ei
ng
Ba
rle
y+
Ba
rle
y
Ba
rle
y+
ot
hy
&
Ti
m
Fi
be
rh
em
p
cl
Fa
ll o
w
ov
er
lo
v
&c
t im
ho
ei
ng
Ba
rle
y+
Ba
rle
y
Ba
rle
y+
Fi
be
rh
em
p
0
Figure 1. Distribution of plant height and growth stages of S. arvensis in 20 Aug 2001, prior to
harvest of barley.
S. arvensis dry mass
300
gm
-2
200
100
Fa
llo
w
&c
lov
er
Ti
m
ot
hy
tim
&c
lov
Ba
rle
y+
ho
ei
ng
Ba
rle
y+
Ba
rle
y
Fi
be
rh
em
p
0
Figure 2. S. arvensis dry mass in 20 Aug 2001.
69
References
HÅKANSSON S (1969) Experiments with Sonchus arvensis L. 1. Development and growth, and
the response to burial and defoliation in different developmental stages. Lantbrukshögskolans
annaler 35, 989–1030.
MEIER U (ed.) (1997) Phenological growth stages and BBCH-identification keys of weed species.
p. 135–139 In: Growth Stages of Mono- and Dicotyledonous Plants (ed. U Meier), BBCHMonograph. Berlin; Wien: Blackwell Wissenschafts-Verlag. 622 p.
ZOLLINGER RK & KELLS JJ (1991) Effect of soil pH, soil water, light intensity, and temperature
on perennial sowthistle (Sonchus arvensis L.). Weed Science 39, 376–384.
70
The action spectrum for maximal photosensitivity of germination and
significance for lightless tillage
K. M. Hartmann & A. Mollwo
Institut für Botanik und Pharmazeutische Biologie der Universität Erlangen-Nürnberg
Staudtstr. 5, 91058 Erlangen, Germany; E-mail: Karl.Hartmann@rzmail.uni-erlangen.de
Abstract
The photosensitivity of the achenes of Garden Lettuce (Lactuca sativa) may differ by a factor of 108
after one week of chilling or warming. To characterize maximal photosensitivity of germination the
action spectrum from 300 to 800 nm was elaborated, based on 20 fluence-response curves for 6 s to
10 min exposure. These run linearly and closely parallel to saturation in the logarithmic probability
net. The apparent photoconversion spectrum, derived for 50 % germination, was corrected for the
transmittance of the seedcoat. It is a photoconversion spectrum of the red-absorbing phytochrome
A, with photoconversion cross-sections of 1.2109 or 4.5103 m² mol-1 at 666 or 800 nm, respectively. This means for half-saturated germination of sensitized lettuce fewer than 1 out of 200,000
molecules of phytochrome A have to be photoconverted to the far-red absorbing form. Hence, no
photoinhibition of the germination by far-red to deep-red light between 735 and 800 nm was found.
Therefore, all spectral colours of nightly moon- or sky-light may stimulate the germination of
highly photosensitized weed seeds, if these are exposed at the soil surface between sequential tillage
operations for more than 5 s or 5 min, respectively.
Keywords: photo-control, Lactuca sativa, Garden Lettuce, Arabidopsis thaliana, phytochrome A,
very-low-fluence response
Introduction
Farming of our land started about 12,000 years ago, at the end of the last Ice Age, and weeds were
only killed by hoeing and burning. During World War Two, after detection of 2,4-D (2,4-dichlorophenoxyacetic acid), chemical control of weeds by herbicides started. In 1952 it was found that
numerous developmental processes of plants can be controlled by light signals, absorbed by
phytochromes (Borthwick et al. 1954; Smith 1995). Photo-control of seed germination is one of the
most sensitive phytochrome reactions ever detected. Therefore, a lot of seeds only germinate if
these are posed close to the soil surface. In this way young seedlings will grow into the daylight
before reserves are used up. This property is typical of most of our small- and brown-seeded weeds,
occurring in agricultural fields (Buhler 1997, Milberg et al. 2000). However, most large- and lightseeded crop plants as evolved by man have been selected to germinate in darkness, because it is
advantageous to place large seeds into the soil, where water and minerals are more readily available
and where the access for birds and other seedeaters is restricted (Radosevich & Holt 1984). This
means that most weeds need some light to germinate whereas crop plants do germinate in darkness.
Every soil cultivation shifts some seeds from the soil seedbank up to the surface into the
daylight and facilitates germination. This is also true for weed seeds that get a flashlight exposure
during tillage operations (Scopel et al. 1994). This way the development of various weeds gets
ahead of the crop plants (Jensen 1995). Therefore, it was possible to demonstrate that three times
repeated nighttime cultivation of agricultural fields might act as an efficient weed killer (Hartmann
71
& Nezadal 1990). However, this method of lightless tillage proved to be unreliable, mainly if
applied only once (Niemann 1996, Fogelberg 1999). One reason is the annual dormancy cycle in
buried weed seeds (Baskin & Baskin 1985). Moreover, dependent on the local climatic and mineral
conditions, the photosensitivity of the seeds in the soil seedbank may reversibly shift by a factor of
108 within one or two weeks (Hartmann & Mollwo 2000 a).
Freshly sown seeds of typical spring germinators, like Garden Lettuce (Lactuca sativa),
normally do not respond to natural night- or moonlight, but short exposures to weak day- or twilight
at dawn or dusk are needed for germination (Frankland & Taylorson 1983, Smith 1995). However,
recently it was shown that germination is triggered by moon- and nightlight if seeds are chilled for
about one week in the imbibed state (Hartmann et al. 1998). During maximal photosensitivity an
exposure to 1 second of a full moon or to 1 microsecond of full sunlight will suffice. This corresponds to the illuminances measured in the open (Figure 1). Therefore, during experimentation with
sensitized seeds no visible safe-light should be used (Hartmann 1977, Baskin & Baskin 1979). For a
better understanding of these problems the action spectrum for maximal photosensitivity of
germination was determined to discuss its meaning for the method of lightless tillage.
lx
5
Full sun, around noon
4
Thunderstorm, at noon
10
10
3
10
Sunset, fair
2
10
Twilight at dawn/dusk
10
1
-1
10
-2
10
-3
10
Full moon, no clouds
One hour after sunset, fair
Night-sky, no moon fair
Night-sky with rain clouds
Figure 1. Spherical illuminances in lux (= lx) along a logarithmic scale, as measured close to
Erlangen in the open. Below rain clouds (= nimbostratus) values drop to about 10 %
(from Hartmann et al. 1998).
Germination conditions
Achenes of the lettuce variety Lactuca sativa L. cv. Grand Rapids, tip-burn-resistant strain (crop
1978), were sealed, stored, selected and sown as described by Hartmann et al. (1998). Sowing was
in 9 cm Petri dishes on 4 layers of washed filter paper (type 595, Schleicher & Schüll, D-Dassel),
using 2.5 mL 0.01 molar KNO3 and 50 achenes per dish. For germination tests up to 20 sown Petri
dishes were stored at 22.5±0.5 °C in metal boxes, tightly closed with black gardening foil and black
72
cloth below the cover. For these conditions and all experiments the 68 % confidence interval of the
dark germination was at 43.3±2.0 % from November 1998 until June 2000.
The sunlight-formed active maternal phytochrome B within the achenes has been depleted by
irradiating with deep-red at 763 nm at an irradiance of 4.5r0.2 W m-2 for 5 min at the second hour
after imbibition, followed by 1 day of darkness at 35 °C. Seven more days of chilling at 3.5r0.3 °C
was given to obtain photosensitized achenes. The pretreated Petri dishes were subsequently exposed
to diverse light through warmed new covers at 22.5r0.5 °C. Handling of the prepared dishes was in
darkness within metal-coated black-walled growth chambers (BBC-York, D-Mannheim), using
black frames for adjustment during exposure. After illumination the Petri dishes were again stored
for at least 2 days in light-tight metal boxes at 22.5r0.5 °C. For further details see Hartmann &
Mollwo 2000 a, b.
Monochromator systems
Deep-red light was filtered from a 2.5 kW xenon arc cinema-projector (Zeiss-Ikon, D-Kiel; Raschke
1967) as described in detail by Hartmann et al. (1998). The isolated deep-red band was centred at
763 nm, with a half bandwidth of 23 nm and a tenth bandwidth of 43 nm, to expose up to 6 Petri
dishes simultaneously at an irradiance of 4.5r0.2 W m-2, corresponding to a photon fluence of
15.5r0.7 mmol m-2 within 5 min.
Red light, centred at 657 nm with a half bandwidth of 16 nm, was emitted from an area of 133
mm² of a black-coated red fluorescent tube (Philips TL 20 W/15, NL-Eindhoven; see Hartmann et
al. 1997), to get 55 cm below the tube a photon irradiance of 6.5 nmol m-2 s-1, this is a photon
fluence of 320r16 nmol m-2 in 30 s.
Table 1.
Parameters of the fluence-response curves for photostimulated germination of sensitized
Lettuce, cv. Grand Rapids tip-burn-resistant strain, as computed from the probit analysis
with Eqs. 3 to 5.
Centre
wavelength
[nm]
800
772
735
694
666
655
618
585
553
520
493
478
449
428
398
377
360
345
321
301
Half
bandwidth
[nm]
24.5
15.0
18.1
14.4
17.4
19.0
17.7
15.6
17.6
16.7
16.0
16.5
16.3
16.4
17.0
8.0
6.7
5.9
5.7
9.1
Half
response
fluence
[nmol m2]
653400
24370
640.9
7.77
3.33
3.89
8.36
27.80
67.35
486.8
1536
1168
767.4
910.8
1707
16470
8440
12650
12860
13760
Factorial
standard
deviation
V
2.26
2.30
2.22
2.29
2.06
2.29
2.17
2.03
2.59
2.14
2.10
2.12
1.97
2.57
2.15
2.70
2.10
2.39
1.81
2.05
Correlation
coefficient
r
0.9537
0.8828
0.8640
0.9135
0.9204
0.9390
0.8860
0.9043
0.9533
0.9458
0.9274
0.9001
0.9352
0.9505
0.9542
0.9709
0.9408
0.9382
0.9512
0.9144
Transmittance of
seed coat
T
0.3403
0.3165
0.2815
0.2745
0.2557
0.2330
0.2183
0.1895
0.1665
0.1560
0.1260
0.1175
0.1037
0.0680
0.0377
0.0183
0.0115
0.0089
0.0097
0.0130
Apparent
Corrected
conversion cross section
[m2 mol-1]
1.53·103
4.10·104
1.56·106
1.29·108
3.00·108
2.57·108
1.20·108
3.60·107
1.49·107
2.05·106
6.51·105
8.56·105
1.30·106
1.10·106
5.86·105
6.07·104
1.19·105
7.91·104
7.78·104
7.27·104
[m2 mol-1]
4.50·103
1.30·105
5.5·106
4.69·108
1.17·109
1.10·109
5.48·108
1.90·108
8.92·107
1.32·107
5.17·106
7.29·106
1.26·107
1.61·107
1.55·107
3.33·106
1.03·107
8.88·106
8.05·106
5.60·106
73
Other monochromatic light was filtered from a modified slide projector (Noris AV 250;
E.Plank, D-Nürnberg), with tungsten halogen bulb Xenophot HLX 24 V 250 W (Osram, D-Berlin),
running at 21.5 V on stabilized alternating current. For wavelengths below 400 nm a xenon arc
projector with quartz optics was used (XBO 450 W by Osram, in Leitz, D-Wetzlar, arranged
according to Mohr & Schoser 1959, 1960). Filtering was by heat filters and interference filters
(Schott, D-Mainz), both air-cooled. Double-bandpass filters of the type DAL were used above 380
nm, line filters of the type UV-IL below 380 nm. The spectral transmittance of all used filters was
measured (Uvikon 860; Kontron, D-München) and cleaned down to <10-4 by combination with
colour filters (Schott, D-Mainz). The realized half bandwidths of all combinations (Table 1) were
3±1 % of the centre wavelengths, and their tenth and hundredth bandwidths were smaller than two
to three times the half bandwidths, respectively.
Light exposures
The normal photon irradiance at the exposure level was adjusted by means of combined neutraldensity filters (Schott, D-Mainz) to values between 0.1 nmol m-2 s-1 at 666 nm and 8 µ mol m-2 s-1 at
800 nm, to obtain within the Petri dishes spherical photon fluxes between 0.18 nmol m-2 s-1 and 14.4
µmol m-2 s-1, respectively. An electronic shutter behind the projection lens modified the exposure
time between 6 s and 10 min (Compur electronic 1; Prontor, D-Wildbad).
Vertical light beams have been measured at the exposure level by means of a calibrated
thermopile system (CA1; Kipp & Zonen, NL-Delft; see Hartmann et al. 1998) and a silicon
photodiode as the monitoring detector (Si 15; Dr. B. Lange, D-Berlin). The entrance port of the
thermopile was closed by a pane of the Petri cover to correct for loss of transmittance, and the 80 %
diffuse reflectance of the non-fluorescent wet white filter paper was added, to obtain the spherical
photon flux within the Petri dishes, i. e. the photon fluence rate.
Evaluation
Light-stimulated germination percentage, G, is based on the emerged radicles as counted in samples
of size N = 50, earliest 2 days after the last light exposure and determined according to the equation:
G = (L – D)/(M – D) with 0 < G < 1,
(1)
with L = number germinated after light exposure, D = number germinated in darkness, and M =
maximal number germinated. G always saturated at 98.8±0.2 %. The binomial random error s of G
is found from the square root of the variance s²:
s² = G(1 – G)/N
(2)
For N = 50 and for G = 0 or 1 we get s < 0.02, and for G = 0.5 s is increasing to 0.071.
Fluence-response curves for germination of lettuce were obtained from 30 to 60 samples,
exposed to at least 10 different photon fluences at each of the 20 spectral bands (Table 1). Three
prepared Petri dishes were always exposed successively to the same photon fluence. The
germination of all samples, determined from Eq. 1, was plotted versus the applied photon fluence,
using the logarithmic probability net, this is germination percentage on a probit scale versus photon
fluence on a logarithmic scale (Figure 2).
Seedcoat transmittance
In addition, the spectral transmittance of the seedcoat was needed. For this purpose six halves of
seedcoats of lettuce were prepared 3 h and 28 h after sowing, and fixed in parallel by means of twosided adhesive tape to a strip of ultra-violet transmitting plexiglass (11345 mm³), to cover an area
of 5 to 7.5 times 3 mm². For these samples the mean spectral transmittance (= T in Table 1) was
measured versus the blank at the entrance port of an integrating sphere, flanked to a spectro-
74
photometer using a projected slit width of 0.10.3 mm² (KA plus objective at M4QIII with PMQII;
Zeiss, D-Oberkochen). The standard deviation of 2 to 4 measurements was ±2.2 % at 800 nm and
dropped to ±0.2 % at 301 nm.
Results
Firstly, in the imbibed achenes of lettuce the maternal phytochrome Bfr has been reduced to the
minimum by saturating deep-red exposure, followed by 1 day at 35 °C. Secondly, achenes were
photosensitized by 1 week of chilling at 4 °C. The elaborated fluence-response curves for photostimulated germination gave good linear regression fits in the logarithmic probability net (Figure 2).
This means that the germination percentage, G, determined from Eq. 1, is increasing according to:
probit G = 5 + (log F – log H)/log V
(3)
where F = applied photon fluence in nmol m-2, H = half-response fluence in nmol m-2 (i.e. for G =
50 %), and V = factorial standard deviation of the sensitivity distribution within the population. This
version of the probit analysis stems from Harpley et al. (1973) and is similar to other approaches (e.
g. Duke 1978, Cone et al. 1985). The computed parameters of Eq. 3, and the correlation
coefficients, r, are listed in Table. 1.
520
585
398
377
800
99.86
7
97.7
6
84.1
5
50
4
15.9
3
2.3
2
0.14
-1
10
1
1
10
2
10
3
10
4
10
5
10
6
10
germination /%
probit
666
8
7
10
-2
photon fluence / nmol.m
Figure 2. Some selected fluence-response curves for photostimulated germination of lettuce fruits,
presented in the logarithmic probability net. Wavelengths in nm are indicated.
A homogeneous photoresponse to all spectral bands from 300 to 800 nm may be assumed,
because none of the factorial standard deviations, V, significantly deviates from their arithmetic
mean, Vg = 2.22 (P > 0.05), stating that all fluence-response curves run almost parallel and go to
saturation. This means that classical action spectroscopy is applicable. Hence, we get the apparent
conversion spectrum of the sensory pigments, or their apparent spectral molar conversion crosssection [= s(O)], if we plot the reciprocal of the spectral half response fluence [= H(O) in Eq. 3]
along the wavelength (Hartmann 1977, 1983; Schäfer et al. 1983):
s(O) = 1/H(O) with the unit [m2 mol-1]
(4)
75
The quantity s(O) is also named absolute spectral photon effectiveness (or responsiveness) and gives
the apparent spectral molar photoconversion cross-section of the controlling pigment(s). This
quantity from Table 1 is plotted on a logarithmic scale versus the wavelength, to show the typical
apparent conversion spectrum of the controlling pigment(s) in Figure 3. In addition, the corrected
conversion spectrum was computed according to:
c(O) = s(O)/T(O)
(5)
2
-1
with c(O) = corrected spectral (molar photo)conversion cross-section in [m mol ] and T(O) =
spectral transmittance of the seedcoat from Table 1.
The typical corrected conversion spectrum derived from Table 1 is shown in absolute and
relative form, along the left and the right ordinate of Figure 3, respectively. Thus, the corrected
molar photo-conversion cross-section at 666 nm reaches a maximum of 1.2·109 m2 mol-1, whereas at
800 nm a minimum of 4.5·103 m2 mol-1 is obtained. This means that for photo-control of
germination the hitting probability or photon effectiveness at 800 nm is only 4·10-6 of 666 nm,
confirming that the long wavelength slope of the conversion spectrum verges into a Gaussian
function, as to be expected for conjugated chromophores and consequently also for phytochromes
(Hartmann & Haupt 1977, 1983; Seyfried & Schäfer 1985).
The pattern of course of the corrected conversion spectrum resembles the conversion spectrum
of phyAr o phyAfr in vitro, as plotted in Figure 3. Therefore, a test for deep-red reversibility was
performed, applying saturating exposures of 320 nmol m-2 at 657 nm and 1.5 mmol m-2 at 763 nm
within 30 s, and 5 min darkness in between. As was to be expected from the fluence-response
curves (Figure 2), fully saturated germination at 100–0.5 % was found for 657+763 nm and
763+657 nm, as well as for 657 nm or 763 nm alone, whereas the dark control gave 5±1.5 %
germination.
10
9
1
10
8
10
10
10
10
7
-1
corrected
-2
10
-3
6
5
10
apparent
-4
10
in vitro x10
10
10
3
-5
4
10
3
10
relative photon effectiveness
10
2
conversion cross section / m mol
-1
10
-6
300
400
500
600
700
800
wavelength / nm
Figure 3. Action spectra for germination of sensitized lettuce, showing the apparent and the
corrected conversion spectrum, in absolute (left ordinate) and relative form (right
ordinate). The given conversion spectrum for phytochrome A in vitro for the transition Pr
o Pfr derives from Lagarias et al. (1987), as listed by Mancinelli (1994) and corrected
according to Hartmann et al. (1997), however multiplied by 1000.
76
Discussion
The corrected action spectrum in Figure 3 is similar to the typical colour curve of the red-absorbing
form of phytochrome A. Both spectra run about parallel above 520 nm. However, down into the
blue and ultra-violet progressively lower photon effectiveness is noted, and no identity to the action
spectrum of the ‘Very Low Fluence Response’ in Arabidopsis thaliana (Thale Cress) by Shinomura
et al. (1996) is ascertained. Nevertheless, some conclusions can be drawn:
Firstly, for sensitized lettuce the half-response fluence at 666 nm is 3 nmol m-2 whereas for A.
thaliana at 655 nm around 25 nmol m-2 was reported (Shinomura et al. 1996). Therefore, lettuce
was at least eight times more photosensitive.
Secondly, for sensitized lettuce all fluence-response curves from 300 to 800 nm run approximately parallel and saturate germination. This indicates that also 800-nm-light forms enough active
phytochrome A to saturate the VLFR in lettuce. However, fluence-response curves for A. thaliana
at 780 nm and 800 nm showed flatter slopes and did not saturate (Shinomura et al. 1996).
Thirdly, accepting phytochrome A as the photoreceptor, the direct comparison of the
photoconversion cross-sections in vitro and in vivo is possible, e.g. at 666 nm. This gives
6131/1.2·109 | 5·10-6, indicating that about 1 out of 200,000 phytochrome A molecules must
become Pfr for half saturated germination. A similar value is also derived from the photoconversion
kinetics of phytochrome A, if for the half-conversion fluence 113 µmol m-2 at 666 nm is used from
Mancinelli (1994). Comparing this to the corrected half-response fluence of germination at 666 nm
in Table1, this is 3.330.2557 | 0.85 nmol m-2, we calculate for 50 % germination and the
photoconverted fraction of phytochrome A a value of | 4.6·10-6 (Hartmann & Mollwo 2000 b).
Thus, for half saturated VLFR of germination fewer than 5 out of 1 million or about 1 of 200,000
phyA molecules have to be photoconverted to Pfr. This corresponds to fewer than 40 molecules of
phyAfr per root meristem cell of 50 µm size and is still high enough for a cellular control
mechanism by phytochrome A (Hartmann & Haupt 1977, 1983).
Fourthly, the slope of fluence-response curves, defined by the factorial standard deviation V in
Eq. 3 and given in Table 1, is a measure for the photosensitivity distribution within the seed
population, approximating a homogeneous Gaussian distribution. For example, at 666 nm about 95
% of the population respond to a photon fluence between 3.3/2.062 | 0.78 nmol m-2 and 3.32.062 |
14 nmol m-2 (see Figure 2).
These findings proof that all spectral colours – from the ultra-violet at 300 nm to the near infrared at 800 nm – saturate the VLFR of germination and that no deep-red reversibility is realized.
Therefore, also 5 s or 5 min of nightly moon- or skylight, respectively, stimulate the germination of
highly sensitized seeds via the VLFR of phytochrome A (Hartmann et al. 1998). This means that
the strategy to reduce the weediness of arable land by cultivation at night might be hampered, as
soon as highly photosensitized weed seeds occur in the seedbank and are exposed at the soil surface
in the imbibed state. Consequently, in a phase of high photosensitivity exposure periods of several
minutes between timely separated nightly or lightless tillage operations should be avoided. This is
also evident from Jensen (1995), reporting increasing weed emergence with increasing number of
nightly soil cultivations. Whether light-shielded tillage equipment can serve for reliable reduction of
the weediness of agricultural fields needs further trials (Ascard 1994, Gerhards et al. 1997, van der
Weide et al. 2002). However, from our findings we have to conclude that an additional far-red or
deep-red exposure during tillage operations is not promising. There is more evidence that germination and emergence of weeds can be inhibited by reburial below 8 cm soil depth (Kasperbauer &
Hunt 1988, Benvenuti et al. 2001).
77
A fundamental limitation of the method of lightless tillage is heterogeneity and variability of
the soil seedbank. Moreover, there are annual dormancy cycles in buried weed seeds, modified by
climatic and mineral factors like temperature, humidity, nitrate and desiccation (Baskin & Baskin
1985, Hartmann et al. 1997, Vleeshouwers 1997). Recently it was demonstrated that the photosensitivity of seeds may reversibly change over eight orders of magnitude within one week
(Hartmann & Mollwo 2000 a). This means that further refining of the method will depend on shortterm predictions on the dormancy state of the weed seeds in the soil seedbank. For this purpose data
on germination, seedlings growth and emergence of weeds in the field must be evaluated as a
function of metereological and mineral data, to gain reliable model-based predictions on the
photosensitivity state of buried weed seeds (Vleeshouwers 1997, Forcella 1998, Forcella et al. 2000,
Grundy & Mead 2000).
Acknowledgements
Financial support by the “Deutsche Forschungsgemeinschaft“ and the “Universitätsbund ErlangenNürnberg“ is gratefully acknowledged.
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79
A degree-day model of Cirsium arvense predicting
shoot emergence from root buds
R. K. Jensen, D. Archer1 & F. Forcella1
Department of Crop Protection, Danish Institute of Agricultural Sciences,
DK-4200 Slagelse, Denmark, RikkeK.Jensen@agrsci.dk, 1North Central Soil Conservation Research
Laboratory, USDA-ARS, Morris, MN 56267, USA.
Abstract
Reliable predictions of weed emergence can be very important in optimizing the timing of
management operations. Most Canada thistle shoots arise from adventitious root buds, and because
many shoots may be interconnected through the perennial root system, the species has an extremely
high regenerative capacity. It is well known that one of the critical periods for perennial weed
management is in the very early stages of shoot emergence, and information on shoot emergence
and early-season growth of Canada thistle is very important in relation to timely and effective
control. For this reason, Donald (2000) collected shoot emergence data in the field for Canada
thistle in North Dakota. A logistic regression model was developed relating emergence to thermal
time, based on air temperature accumulated from April 1.
The objective of this study was to generalize the model described by Donald (2000) to predict
emergence of Canada thistle in other locations. In modeling annual weed phenology, Forcella et al.
(2000) showed that soil temperature is one of the main environmental factors affecting seedling
emergence. Consequently, the second objective of this analysis was to determine whether soil
temperature, instead of air temperature would improve predictions of shoot emergence. Cumulative
shoot emergence data from Donald’s (2000) figures were digitized. These data were recorded
during 1987 and 1989 in field experiments at the research farm of North Dakota State University in
Fargo. Climate data for the same years and from the same site were obtained to convert temperature
into growing degree-days. Additionally, four field experiments were conducted in 2001, 20 km
from the Research Centre Flakkebjerg at the Danish Institute of Agricultural Sciences. The field had
a natural and long-term infestation of Canada thistle and the experiments consisted of four cropping
systems. All the cropping systems contained subplots with and without under-sown pasture species.
However, because neither the cropping systems nor the sub-treatments had any effect on thistle
phenology, they were not considered further in the analyses. Thermal time (cumulative growing
degree-days GDD) were calculated and accumulated with a base temperature of 0 C.
The logistic model based on the shoot emergence data from North Dakota slightly
underestimated the shoot emergence of the Danish data. However, it was found that the date of
seedbed preparation was a better starting date for accumulating thermal time in tillage systems.
Changing the date of initial heat accumulation gave the relationship of shoot emergence and thermal
time of all three data sets a more uniform appearance. Although the logistic function gave a good
estimation, a Weibull function gave a better fit especially at the low emergence levels. Further, a
Weibull function based on cumulative soil thermal time explained more variation (r2=0.96) than the
same model using accumulated air temperature.
80
The Weibull function model predicting shoot emergence based on accumulated soil
temperature from seedbed preparation was:
Y = 1(1-exp(-(4.3219(GDD)2.9638)))
The model is based on data sets that transcend time and continents, capturing much of the
variation in shoot emergence and is for that reason expected to be robust.
However, the model can only predict shoot emergence and not development stages. Further, the
model is only based on shoot emergence data from well-established stands of Canada thistle. To
optimize the timing and effect of mechanical treatments the model should be based upon shoot
emergence and development through time from establishment or from the last control operation. In
addition, the model also should be able to predict plant height, plant number and development
stages successfully.
Reference
DONALD WW (2000) A degree-day model of Cirsium arvense shoot emergence from adventitious
root buds in spring. Weed Science 48, 333-341.
FORCELLA F, ARNOLD RLB, SANCHEZ R & GERSHA CM (2000) Modeling seedling
emergence. Field Crops Research 67, 123-139.
81
Weediness in 40- year period without herbicide
L. Zarina
Priekuli Plant Breeding Station, LV-4126, Cesis, Latvia
E-mail: pr_sel@apollo.lv
Abstract
The competitive struggle between weeds and the crop plant takes place under very unequal
conditions. As wild plants, weeds generally have the advantage over cultivated plants through their
greater vitality and their usually lower demands on growth factors. Weeds with branched, vigorous
root systems make nutrient deprivation. Additional fertilizer, intended as compensation for
nutrients, is lost to the crop. If the farmer does not interfere in favour of the disadvantaged crop
plant, the struggle is often very quickly decided, and bad harvest or even ploughing under there is
the result.
The most simple weeds control is by using of accordant herbicide, but apropos of increasing of
interest in organic farming there are interest in mechanical and biological weed management to
increase. To give answers on the questions- it is possible to provide economically based crops
yields without herbicide? How big is the role of crop rotation? - analyse of results of long term crop
rotations experiments were provided.
The experiment is located in Priekuli (57o19'N, 25o20'E) on a soddy podzolic light loam with the
following characteristics in the year of establishing (1958): organic matter content 2.1 %, soil
pHHCl 5.8 to 6.1, P2O5 80-100 mg kg-1, and K2O 100-120 mg kg-1. The normal mean temperature
varies from -6.2 0C in January to 16.7 0C in July. The mean annual rainfall is 691 mm.
The experiment included five different crop rotations: 1. barley- potato- barley or oat; 2. barleyclover/grass-rye- potato; 3. barleyclover/grass- barley- rye- barley- potato; 4.barleyclover/grass- potato; 5.barley -clover/grass- clover/grass- rye- barley- potato.
Five different fertilisation treatments are compared with the crop rotations as sub-plots within each
fertiliser treatment: 1. unfertilised; 2. farmyard manure, 10 t ha-1 till 1980 and 20 t ha-1 from 1981
(incorporated in soil in autumn before potato; 3. 66 kg N, 90 kg P, 135 kg K ha-1 ; 4. farmyard
manure, 20 tha-1 plus 66 kg N, 90 kg P, 135 kg K ha-1 ;5. 130 kg N, 180 kg P, 270 kg K ha-1
In 1959, 22 tha-1 of spring lime was given. Measurements of soil nutrient content and of crop yield
were performed every year. No pesticides were used.
During 40-years period, the influence on weediness of field was fixed. The most prevalent weeds
were: Chenopodium album, Galeopsis tetrahit, Spergula arvensis, Stellaria media, Matricaria
inodora, Centaurea cyanus, Viola arvensis, Taraxacum officinalis, Cirsium arvensis.
The best crop rotation for providing of economically based crop yields are crop rotations with
including of clover of 25-30%.
Inter- and intra-row mechanical weed control
82
83
Relationship between speed, soil movement into the cereal row and
intra-row weed control efficacy by weed harrowing
1
A. Cirujeda1, B. Melander2, K. Rasmussen2, I. A. Rasmussen2
Departament d’Hortofructicultura, Botànica i Jardineria; Universitat de Lleida; Avda. Alcalde
Rovira Roure 177; 25198 Lleida-Spain
2
Department of Crop Protection, Danish Institute for Agriculturl Sciences, Research Centre
Flakkebjerg; DK-4200 Slagelse-Denmark
Abstract
Field trials were conducted at one Danish and two Spanish locations. Winter wheat was sown at
24 cm spacing in Denmark allowing hoeing in the inter-row area. Hoeing speeds of 2, 5 and 8 km h1
were tested at the end of tillering stage, at the beginning of crop elongation and at both times.
Harrowing was conducted immediately afterwards at the same speed. In the Spanish locations, only
harrowing was conducted in winter barley sown at a row distance of 12 cm at pre-emergence +
post-emergence and post-emergence alone at mid of tillering at 2, 4, 6 and 8 km h-1. The depth of
the soil layer thrown into the cereal row was measured. This layer ranged between 0.4 and 1.4 cm
depending on the site and on the treatment but was generally higher with a single treatment at all
sites. A soil layer increasing with higher speed was found only in the Danish location when a single
treatment was conducted at crop stage 22-24. Comparing soil types, in a more sandy soil and in a
soil rolled prior to treatment, less soil was thrown into the cereal row. When two hoe + harrowing
treatments were conducted, a finer soil structure was achieved. However, this did not affect the
weed control. In the Danish location, initial intra-row efficacy based on plant number 7 days after
treatment was found low (20-40%) but increased up to 70-80% when assessed after 45 days. Burial
together with plant competition probably supressed weed plant growth and enhanced final
mortality. In the Spanish locations, efficacy ranged also between 70-80%.
A thicker soil layer did not result in a higher efficacy. It was, thus, supposed that burial alone
could not be the main factor responsible for weed control in any of the studied cases. Despite of the
irregularity, the soil thickness thrown into the row was found to be a useful parameter for
comparing the thickness of the soil layer on plants between different locations, but was found not
appropriate to predict the weed control efficacy.
Introduction
A lot of work has been done since the 50’s on weed control by harrowing. Several studies have
been conducted in Germany before the intensive use of herbicides (Habel 1954, Kees 1962, Koch
1964). The next big flush of research started in the late 80’s following the need of improving weed
control methods alternative to herbicides for organic farming. Also the environmental concerns and
the problems of herbicide resistance have enhanced these studies.
Field experiments have been conducted in order to find out the best timing, speed and
implements (Rasmussen 1990, 1991, 1992, 1993; Böhrnsen 1993; Wilson et al. 1993; Rydberg
1993, 1994; Welsh et al. 1997). Simulations have been done recently in pot experiments in order to
find out, which are the main factors causing mortality in plants with the aim of improving the
control techniques (Cavers & Kane 1990; Jones et al. 1995, Jones & Blair, 1996; Baerveldt &
Ascard 1999; Kurstjens et al. 2000; Kurstjens & Kropff 2001).
84
Despite so much research, many aspects of mechanical weed control are still unclear or could
be improved (Bàrberi et al., 2000; Kurstjens & Kropff, 2001). Regarding the weed control in
cereals, low intra-row efficacy is known to be one of the weak points of weed harrowing, especially
when the cereal plants have already reached the tillering stage (Rasmussen & Svenningsen, 1995).
On the other hand, this is a strong point for the crop resistance towards mechanical weed control.
Nevertheless, no studies on the processes occurring in the intra-row space have been published.
There is an interest for establishing experiments focusing on the processes occurring in the
intra-row space in very different locations in order to adapt the mechanical weed control methods to
each area. In Denmark and other Northern countries, the usually wet and cold autumn and winter
makes harrowing difficult at this time (Koch 1964, Wilson et al., 1993). Treating the winter wheat
in late autumn or winter can result in severe damage making recovery difficult and decreasing the
yield (Rasmussen 1990, 1998). Often in spring, weeds germinated in autumn have grown large and
are not well controlled by harrowing. Because of this, alternative methods are investigated, as e.g.
increasing the row distance in order to be able to hoe. This method combined with weed harrowing
has shown to improve the weed control efficacy (Melander et al., 2001). Still a weak point is the
weed control in the cereal row, as it is in the row crops such as onions, carrots and sugar beet
(Rasmussen & Ascard, 1995).
Also the influence of speed on the harrowing efficacy is not very clear. Rydberg (1994) and
Rasmussen & Svenningsen (1995) tested different speeds in order to achieve different degrees of
intensity in weed harrowing, reflecting the general opinion that the speed influences soil movement.
Rydberg (1993), however, found that the reduction of weeds and of grain yield correlated much
better with the degree of soil cover than with the driving speed. Concluding from other experiments,
Rydberg (1994) described that increased driving speed caused more soil cover but only a limited
increase in weed effect. He also found most of the weed efficacy was attained at 5 km h-1 so that
higher speeds did not improve the weed control. Also Böhrnsen (1993) quotes the dependency of
harrowing efficacy on the speed. And Rasmussen (1990) found it difficult to establish a relationship
between speed and weed control.
Some confusion on the effect of covering and uprooting of the weeds exists in mechanical
weed control, specifically in harrowing. While older works show that burial is the most important
factor causing weed control (Habel 1954, Kees 1962 and Koch 1964), recent findings (Kurstjens et
al. 2000, Kurstjens & Kropff 2001) show how the fraction of uprooted plants is important for the
final weed control efficacy even in small plants.
Rasmussen (1996) also criticises that the quantification of the needed intensity of postemergence harrowing is still a question of feeling. In the present work, a soil-based measure, the
depth of the soil layer thrown into the row, was used to quantify the effect of weed harrowing on
the weeds growing in the row and it was evaluated whether it would be a useful parameter for
quantifying the post-emergence intensity. This objective measure also aims to relate the harrowing
to the effect on the weeds as the visually measured crop cover proposed for predicting crop damage
by Rasmussen (1990). The same author found a relationship between crop cover and weed control
efficacy defined as selectivity (Rasmussen, 1990). In the present case, however, the measure is
objective, aiming to allow comparisons between experiments and locations.
Baerveldt & Ascard (1999) also conclude from their laboratory coverage experiments that the
exact depth of the soil layer on the plants needed for control will depend on the plant species, size
of the plants and soil particle size. Any fieldwork related to the quantification of these parameters
could contribute to improve the mechanical weed control methods.
85
The objectives of this work were:
-
To contribute to the study of intra-row processes occurring in mechanical weed control by
measuring the depth of the soil layer in the row in an objective way and in one case also by
weighing the soil aggregates after the treatments.
To test the relationship between speed and efficacy in the cereal row at different locations with
different soils and on weed species with different growth habits.
To study the relationship between the thickness of the soil layer thrown into the row and the
harrowing effect and to find out if this measure can be an objective physical measure for intrarow efficacy. This way, some new data would be added for discussion.
Experiments were conducted at three locations: Flakkebjerg (Sealand, Denmark), Nalec and
Baldomar (Catalonia, Spain). The Danish field belongs to the Flakkebjerg Research Station while
both experiments in Spain were conducted on commercial fields. Four blocks with randomly
distributed plots were established in Flakkebjerg and three in the Spanish experiments.
In Flakkebjerg, winter wheat cultivar Ritmo was grown at 24 cm row spacing, which is double
the normal 12 cm row spacing, so that hoeing could be conducted in the inter-row area with a 16 cm
wide hoe. The seed rate was the same as normally but as spacing was double, double wheat density
was sown in the row. A post-emergence harrow treatment with a tine weed harrow trademark
Rabewerk was conducted immediately after the hoeing at the same speed. The soil, which was
thrown into the row, was the combined effect of these two implements. A post-emergence treatment
was conducted in early April and a second treatment approximately two weeks later (Table 1).
Some plots were treated one time only early, one time only later and others were treated at both
times. The main weeds in Flakkebjerg were Brassica napus (rape sown out as weed the same day as
the crop) and Stellaria media.
The wheat crop stage was mid tillering at the first treatment and starting pseudostem elongation
at the second treatment, while the tap-rooted B. napus already had an erect stem and an average of 4
leaves both times, but started to flower in some cases at the second treatment. S. media had a
diameter of 9 cm at the time of the first treatment and of 11.5 cm at the time of the second
treatment. Before the first treatment mean of plant number was 77.1 B. napus plants m-2 and 28.6 S.
media plants m-2. Before the second treatment, mean of weed number in all the plots was 64 B.
napus plants m-2 and 31.4 S. media plants m-2.
86
Table 1: Description of the experimental sites. Post-emergence harrowing was conducted once
early, once later or both times in the Danish trial, whilst post-emergence alone and
combined with pre-emergence was conducted in Spain.
Location and
soil type
Treatment
date
Crop
growth
stage
(BBCH)
Speed
(km h-1)
Flakkebjerg
(DK)
sandy loam
10/04/00
28/04/00
23-24
30
2, 5, 8
Nalec (E)
silt loam
01/12/00
02/02/01
22-24
2, 4, 6, 8
Baldomar (E)
loamy sand
15/11/00
13/02/01
22-24
2, 4, 6, 8
Plot size
Treatments
1.
2,5 m x 10 m 2.
3.
1.
2.
3 m x 10 m
3.
3 m x 10 m
Post-emergence alone early
Post-emergence alone late
Post-emergence early + late
Post-emergence alone
Pre- + post-emergence
Rolling + pre- + postemergence
1. Post-emergence alone
2. Pre- + post-emergence
Three pairs of flat wooden sticks measuring 3 x 0.3 x 32 cm marked the fixed measuring area at
1 m distance between two sticks in each plot at all three locations. They were placed inside the
cereal row parallel to its direction. The soil level was marked on both sides of each stick before and
immediately after harrowing. Measures were conducted in the early treated plots and in the twice
treated plots. The sticks were placed deep enough to withstand the treatment without tilting. After
removal, an average soil layer per measure was calculated. Twelve measures resulted per plot,
summing to a total of 48 measures per treatment in Flakkebjerg and 36 measures per treatment in
Spain.
Counts of alive plants were conducted in three 0.1 m2 frames 0.10 m wide and 1 m long per
plot in the same measuring areas, where the soil thickness was determined. Assessments were done
7 and 45 days after the first treatment and 7 and 27 days after the second treatment. An untreated
control plot and a herbicide-sprayed plot were included in each block. 7.5 g ha-1 a.i. tribenuronmethyl + 1.25 L ha-1 a.i. isoproturon were sprayed in autumn. In order to obtain more data on the
relationship between the soil structure and the weed intra-row efficacy, an additional assessment
was conducted in the Danish site after the hoe+harrow treatments. The 20 biggest soil aggregates
found in a 0.2 x 0.2 m2 frame in the inter-row area were collected 6 days after the second treatment
and weighed with a field balance.
In both experiments conducted in Spain winter barley cultivar Graphic was grown at the
conventional row distance of 12 cm. A post-emergence harrowing was conducted in February as
well as the combination of a pre-emergence harrowing with the post-emergence treatment. The used
tine harrow was trademark Einböck and 3 m wide. In Nalec, the additional effect of a roll was
studied. Following the traditional practice, the cereal was rolled few days after sowing allowing the
seeds and seedlings to have a closer contact to the earth and preventing lack of moisture. Papaver
rhoeas was the major and almost only weed species. Only the tap-rooted weeds namely P. rhoeas
and B. napus were considered for comparisons between the three locations.
At treatment, the cereal was in early tillering stage at post-emergence treatment while the taprooted P. rhoeas was in rosette stage of 0.7 to 3 cm diameter. In both locations an untreated plot
was included in each block and in Baldomar, a pre-emergence herbicide (trifluraline+linuron at
0.720 + 0.360 L a.i. ha-1 was sprayed in one plot of each block. Weed density and soil measures were
recorded in the same way as in the Danish trial. In Nalec, counts were done 17, 45 and 66 days after
87
treatment; in Baldomar, assessments were conducted 23 and 45 days after treatment. P. rhoeas
density before the post-emergence treatment was around 260 plants m-2 in the untreated plots in
Nalec and around 104 plants m-2 in the untreated plots in Baldomar.
Slow, middle and fast speed treatments were conducted at the three sites (Table 1). The speeds
used were similar to the ones used in other experiments. Rasmussen (1992) used 4-7,5 km h-1,
Wilson et al. (1993) used 8,2 km h-1, Kurstjens & Kropff (2001) used 5,4 up to 8,6 km h-1. Rydberg
(1994) tested very aggressive speeds namely 5, 9 and 13 km h-1.
Efficacy was calculated comparing the plant number in each plot before and after harrowing for
the counts: > % Efficacy = (1- Ta/Tb)*100] where Tb is the infestation in the treated plot before
treatment and Ta is the infestation in the treated plot afterwards@.
The climatic conditions on the field sites during the experimental period are shown in Fig. 1.
During the cropping season 432.6 mm rain was collected at Flakkebjerg, 372.2 mm at Baldomar
and 262.0 mm at Nalec. The main difference between the Danish and the Spanish locations was the
distribution of the rainfall, and a much higher evaporation in Spain, resulting in a more or less
continuous moisture availability guaranteed only in Denmark. After a quite moist November and
December for the local Spanish conditions, the rest of the winter and spring was dry. In
Flakkebjerg, the spring was quite wet but this had no influence on the harrowing timings.
Figure 1. Monthly mean Temperature (line) in oC and monthly precipitation (column) in mm in the
experimental sites during the cropping season at the experiment. A) Flakkebjerg
(Sealand, Denmark). Data from the local climatic measuring station at 59.317o latitude,
11.417o longitude and 31.5 m altitude. B) Baldomar (La Noguera, Catalonia, Spain).
Data from the nearby observatory in Vilanova de Meià located at 41.991º latitude, 1.022º
longitude and 590 m altitude. C) Nalec (Urgell, Catalonia, Spain). Data from the nearby
observatory in Tàrrega located at 41.668º latitude, 1.164º longitude and 420 m altitude.
The horitzontal line indicates the cropping season.
60
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88
Figure 1 (continued)
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J
F
M
A
M
J
J
A
Precipitation (mm)
Temperature (oC)
C
89
Data was subjected to an ANOVA-analysis using the SAS system (SAS, 1991). In the case of
statistically significant differences found, means were separated using the Duncan’s test.
Speed related to soil cover
Similar soil thickness ranging between 1 and 1.4 cm was thrown into the row in the Danish
experiment and in Nalec; in these two locations the soil texture was similar, which could explain the
similarity despite the different treatments in the two locations. Less soil was moved in the rolled
experiment in Nalec and in the loamy-sand soil in Baldomar (0.4 to 0.8 cm) (Fig. 2a). In
Flakkebjerg, less soil tended to be moved in the two-times than in the one-time treated plots. In
Baldomar, a lower soil cover was found in the plots harrowed in pre- + post-emergence than
harrowed in post-emergence only (P<0.05). In Nalec, less soil cover was found in the pre- + postemergence harrowed plots using the roll than in the other two treatments (P<0.001).
Figure 2a. Soil layer (cm) thrown into the cereal row and efficacy in the three locations Baldomar,
Flakkebjerg and Nalec for the different treatments. Efficacy for B. napus in the Danish
location and for P. rhoeas in the Spanish sites after 45 days in all cases. Different letters
refer to significant differences for the soil layer after the Duncan mean separation test
(P<0.05). No differences were found for efficacy.
100
1.6
A
Soil layer
Efficacy
90
a
1.4
ab
80
ab
1.2
70
bc
60
cd
0.8
50
de
Efficacy (%)
Soil layer (cm)
1
40
0.6
e
0.4
30
20
0.2
10
0
0
Postem.
Pre- +
Postem.
Baldomar
Postem.
2 times
Postem.
Flakkebjerg
Postem.
Pre- +
Postem.
Roll + Pre- +
Postem.
Nalec
Probably, soil is thrown into the row in bigger earth pieces but in a more irregular way in the
hoed plots, while harrowing has a more constant effect. By making an average of the soil cover on
90
each stick, however, these differences were probably evened, so that the average was similar in
spite of the different aggregate sizes. The drier soil in the Spanish trials could also be moved more
easily. Rydberg (1994) also observed that in drier conditions more soil movement happened.
Apparently, the amount of soil moved by hoeing + harrowing in wet soil was comparable to the
amount of soil moved by harrowing alone in drier soils.
In the early treatment conducted at the Flakkebjerg location, more soil was thrown into the row
with increasing speed (P<0.05) (Fig. 2b). In these hoed + harrowed plots, this observation is as
expected. More speed caused more soil movement and therefore more soil was thrown into the row.
Figure 2b. Soil layer (cm) thrown into the cereal row in the one-times hoed + harrowed treatment
in Flakkebjerg and weed control efficacy on B. napus and on S. media depending on the
driving speed. Different letters refer to significant differences for each line after the
Duncan mean separation test (P<0.05).
3
2.8
85
B
2.6
m
80
m
2.4
z
m
z
2.2
75
z
2
1.8
b
ab
1.6
1.4
1.2
70
65
a
1
60
2
3
4
5
6
7
8
-1
Speed (km h )
Soil cover
Efficacy on B. napus
Efficacy on S. media
In Baldomar, more soil was found in the only post-emergence harrowing treatment at 4 km h-1
compared to the other speeds (P<0.05), but no tendency of increasing soil cover with increasing
speed was found. In the one-times harrowed plots in Nalec, there was a tendency of soil layer
increase with increasing speed. In the other cases, in which more than one treatment was conducted,
no dependency on the speed for the soil layer was detected in any case. In the harrowed plots the
soil is moved faster by all the tines with increasing speed, so that one tine compensates the soil
movement of the other. This way, increasing speed is not expected to throw a thicker soil layer into
the row. Moreover, the harrow probably evens the soil, causing a more equal soil layer than the hoe.
These results are consistent with the observations of Rydberg (1994) who described only a
moderate increase of soil cover on the weeds by harrowing with increasing speed.
91
A second treatment did not enhance the relationship between speed and soil cover neither in the
hoed + harrowed nor in the harrowed plots and tended to decrease the layer in all cases (Fig. 2a).
Speed related to intra-row efficacy
No increase in efficacy was observed with increasing speed in any case. Only in the postemergence treatment in Baldomar there was a tendency of more efficacy in the 4 km h-1 treatment
compared to the other tested speeds (data not shown). This was also the speed, which resulted in
most soil cover. Differences between locations and between timing were also non-significant (Fig.
2a). Two-times treatments did not lead to higher control than one-time treatments. In the Spanish
trials, the crop and P. rhoeas plants were less developed than the crop and B. napus in Denmark at
the harrowing time. However, a very similar intra-row efficacy was obtained in the Spanish and in
the Danish experiments ranging between 72 and 77% 45 days after treatment. (Fig. 2a).
This general lack of relationship is not consistent with the normal visual observation of the
harrowing effect, which usually relate more speed to more efficacy (Rydberg 1994 and Rasmussen
& Svenningsen 1995). Kurstjens et al. (2000) also found higher working speeds promoting
uprooting in laboratory experiments with small seedlings. Anyway, Rasmussen (1990) did not find
a clear relationship between forward speed and weed control, either. And Rydberg (1994) found
most of the weed reduction already at 5 km h-1 compared to 9 and 13 km h-1, so that a speed
increase did not have an important effect on efficacy.
A very similar behaviour was observed for B. napus and S. media control in the Danish trial for
both treatments (Fig. 2b). Despite the different root system of the two species and the different
growth habit (erect for B. napus and postrate for S. media) the plants in the row reacted in a very
similar way. Again, speed did not have an influence on the efficacy (data not shown). The
explanation could probably be that in both species burial was not the main mortality cause.
Figure 3. Efficacy on plant number (%) on B. napus and on S. media in Flakkebjerg 7 and 45 days
after treatment. Different letters refer to significant differences after the Duncan means
separation test (P<0.01).
100
90
B. napus
S. media
a
80
a
a
a
70
Efficacy (%)
60
50
40
b
30
b
b
b
20
10
0
Postem. T+7
Postem. T+45
2 times
Postem. T+7
2 times
Postem. T+27
Postem. T+7
Postem. T+45
2 times
Postem. T+7
2 times
Postem. T+27
92
Soil cover related to intra-row efficacy
No clear relationship between the soil cover and the intra-row efficacy was found for most of
the experiments. Thus, higher soil cover did not lead to higher efficacy. The best relationship was
found for the early treatment in the Danish trial (Fig. 2b). Again, the behaviour of both weed
species studied in this location, B. napus and S. media was very similar. More control should have
been expected for S. media than for B. napus as the first species is more easily covered than the
second one. Nevertheless, as most of the plants were quite big, few S. media plants were completely
covered so that partly covered plants probably survived. Additionally, S. media has a big regrowth
capacity.
In the case of the Danish experiment, the hoe width left 4 cm of each side of the crop row
untreated. Thus, in the measured 0.1m x 1 m space the main processes, which could be responsible
for the weed mortality, were burial due to the soil thrown into the row by the hoe and the combined
effect of burial and uprooting caused by the harrow. In the Spanish locations, the possible mortality
factors were the combined effect of burial and uprooting caused by the harrow. Due to the lack of
relationship found between the soil layer and the efficacy in the present experiments, the main
mortality factor was probably the uprooting and removal of the plants, more than the burial, as
found also by Kurstjens & Kropff (2001) with small seedlings. In fact, high amounts of S. media
plants were found hanging on the harrow tines at the end of each pass, especially in the later
treatment, as also observed by Wilson et al. (1993). This was not observed for the other two weed
species.
In the experiments described by Bàrberi et al. (2000) the burial depth of the harrow tines
adjusted to the different possible positions was measured. A deeper working depth of the tines,
which probably also resulted in a higher coverage of crop and weeds by the loosened soil, did not
clearly result in higher weed biomass reductions, either. Probably the main mortality cause in these
experiments was not the burial of the weeds.
In the case of the tap-rooted plants, a low efficacy ranging between 20 and 40% was found for
B. napus short time after treatment even in the two-times treatment (Fig. 3). In fact, few rape plants
could be expected to be uprooted any more due to the advanced growth stage, so that main efficacy
was probably due to burial or bending combined with burial. These observations are consistent with
the findings of Kurstjens & Kropff (2001) who describe from their experiments that covering
contributed less to mortality than uprooting assessed 6 days after treatment on small seedlings. In
the present case, this efficacy, however, increased in field conditions up to high levels (Fig. 3). On
one hand, some damaged plants could have finally died after some days. On the other hand, a
possible explanation is that the crop had probably a higher competition ability after the first weed
number reduction. Additionally, crop plant number was double as normal in the row, competing
more than normal with the surviving weeds.
Also Kurstjens & Kropff (2001) state that plant species, growth stage and soil and weather
conditions after harrowing may influence the impact of burying and uprooting on the final
effectiveness of harrowing, as it was observed in the present experiment.
In pot experiments, Baerveldt and Ascard (1999) found that 1.5 cm tall tap-rooted S. alba
plants were able to grow through a soil layer of up to 3 cm. In the present experiments, B. napus
was only partially covered due to its big size and soil thickness was between 0.6 and 1.6 cm
approximately, so that no important mortality could be expected by burial alone.
93
In Spanish conditions, high efficacy was found already in the earliest counts (data not shown)
probably due to the smaller size of both crop and weed plants at the treatment. So, on one hand,
harrow tines could better enter the row in the Spanish experiments and on the other hand, weeds
were smaller and plants could better be uprooted. In the Spanish trials, no increase in efficacy was
observed with increasing soil cover, probably because burial was not the main mortality cause,
either. Our results are consistent with Jones & Blair (1996) who found in pot experiments that P.
rhoeas is susceptible to both uprooting and burial, but mainly to uprooting, regardless of the tested
moisture conditions. The case of P. rhoeas in rosette stadium was more comparable to Matricaria
inodora in the experiments conducted by Baerveldt and Ascard (1999) than to B. napus in the
present experiment. These authors found no survival for plants covered by a 3 cm soil layer but
45% survival with the 2 cm layer when M. inodora was 1 to 2 cm high (comparable to P. rhoeas in
the present experiment). The soil thickness found in the present experiment was between 0.6 and
0.8 cm, so that survival had to be expected. These data support the idea that uprooting or at least the
combination of burial and uprooting was the main mortality factor for P. rhoeas in the present
experiment.
At the Spanish locations, natural weed mortality affected the harrow efficacy. The main natural
plant number decrease, however, occurred after the harrow had already caused its control effect. It
probably contributed mainly to making the recovery process of damaged weeds more difficult.
Table 2 shows the data of the percentage of mortality in the untreated control plots.
Table 2: Natural plant mortality (%) in the untreated plots in the Spanish experimental sites Nalec
and Baldomar. Mean ± SD. DAT = days after treatment.
DAT
Mortality
DAT
Mortality
Nalec
17
14.7±15.77
Baldomar
23
3.6±4.5
45
32.0±22.74
66
46.1±22.56
45
36.5±8.49
More rainfall in Baldomar (Fig. 1) was also reflected in less plant mortality compared to Nalec.
If included in the efficacy calculations, this mortality would have decreased efficacy in time, the
opposite of the behaviour observed in Denmark. The explanation could be that competition
probably affected mainly smaller plants, present in the untreated plots. Less and probably mainly
larger plants survived in the harrowed plots, so that less mortality was recorded among them.
94
Description of the soil structure after treatment
At the Danish site, different-sized aggregates were found in the inter-row space after the
treatments (Fig. 4). The soil weight was measured in the inter-row space, but it represents the soil,
which was thrown into the row, so that it was considered that its size could have a relationship with
the processes occurring in the intra-row space.
Although the early treatment was conducted in a wetter situation than the later treatment, the
size of the aggregates was very similar (Fig. 4). Statistically significant differences were found
between the two-times treated plots and the other plots (P<0.001). The smaller-sized soil aggregates
can cover weed and crop plants in a more homogeneous and effective way. The tendency of the
wheat biomass reduction in the two-times treated plots commented previously could be explained
this way. Also Baerveldt & Ascard (1999) found in laboratory experiments that finer particle sizes
had a bigger control effect after covering the plants.
Figure 4. Weight of the 20 biggest soil aggregates found in 0.2 x 0.2 m frames collected between
the rows. A hoe+harrow treatment was conducted in early April, in late April or both
times. LSD=Least signifficant difference with P<0.01.
450
Weight of the 20 biggest aggregates (g)
400
LSD = 36.1
350
300
250
200
150
100
50
0
2
3
4
5
6
7
8
Speed (km h-1)
early
late
both
Increasing speed reduced the aggregate size, especially the 8 km h-1 treatment (P<0.001). In
spite of this, a much finer soil aggregate size was achieved with the two-times treatment than with a
high speed in a single-treated plot. Referring to the weeds finer soil was not related to higher
efficacy on weed number (Fig. 2a).
95
Conclusions
Soil layers between 0.4 and 1.4 cm were found in the different sites. Speed was related to the
soil layer in the one-time hoed + harrowed treatment, only, but not to the weed control efficacy.
Two-times harrowing or two-times hoeing + harrowing resulted in smaller soil layers but not in
lower efficacy. Two times hoeing + harrowing reduced the aggregate size but did not improve
efficacy, either. The main weed mortality factor was, thus, not caused by burial.
In spite of the irregularity, the soil thickness thrown into the row was found to be a useful
parameter for comparing the thickness of the soil layer on plants between different locations, but
was found not appropriate to predict the weed control efficacy.
The present work confirms the opinion of Wilson et al. (1993) and Welsh et al. (1997) that taprooted weeds are better controlled at early growth stages, as in the Spanish trials P. rhoeas was
better controlled in February than B. napus in Denmark in April. However, it was found that
additional mortality of B. napus by crop competition increased the final efficacy up to the same
levels as obtained for P. rhoeas.
Acknowledgements
The authors thank the technicians in Flakkebjerg: Henrik Grøndal, Trine S. Nielsen, Helle
Petersen, Christian and others in the Danish experiments who assisted in the field even in rainy and
cold conditions and Antonio Roque in the Spanish experiments. Alicia Cirujeda thanks the Spanish
Ministry of Education and Sciences for the FPU grant, which allowed and supported economically
this exchange.
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97
Experiences and experiments with new intra-row weeders
Piet Bleeker 1, Rommie van der Weide 1 and Dirk Kurstjens 2
Applied Plant Research P.O.Box 430, 8200 AK Lelystad, The Netherlands.
2
Wageningen University, Soil Technology Group, P.O. Box 43, 6700 AA Wageningen,
The Netherlands.
Email: p.bleeker@ppo.dlo.nl , r.y.van.der.weide@ppo.dlo.nl and dirk.kurstjens@user.aenf.wau.nl
1
Introduction
The Dutch government aims at 10 % organic farming (area) in 2010. One of the problems is
weed control special in the crop row. Several mechanisation companies in the Netherlands and
Belgium have developed new equipment (different types of fingerweeders, a torsionweeder, a rotary
weeder and a powered spike harrow) for weed control. In the Netherlands, a lot of new machinery is
introduced. Researchers are asked to give an answer to the questions: What improvements are
achievable using the new machinery as compared to the equipment presently used by farmers? In
which crops and growth stages can the new equipment, are used?
The first Dutch trials with fingerweeders and torsionweeders were done in planted leek and
planted iceberg lettuce in 1998 and 1999. Every year each crop was grown and cultivated on two
soil types (sand and clay). Two weeks after planting, the first time of weed control started with the
harrow, the fingerweeder and the torsionweeder in combination with a hoe. In lettuce, weeding was
performed one time and in leek two or three times. Weed control was assessed by counting weeds
immediately before and after weeding at permanently marked areas. Crop plant numbers were
counted and crop yield was assessed.
Research in onion and sugar beet started in 2000. The sugar beets were grown on sandy soil
and the onions on clay soil. In 2001, these experiments were repeated and a trial with sugar beets on
clay was carried out. In the trials with onions and sugar beets only intra-row, weeds were counted
(in strips that were not disturbed by the hoe, with a width of 10 cm in sugar beets and 6 cm in
onions).
Results
Weed control in planted crops such as leek and iceberg lettuce was improved by using the new
machinery. In both crops, the fingerweeder yielded the best weed control and was selective for the
crop too. On sandy soil, weed control was above 95 %. The torsionweeder gave a good result too.
However, it was a little more aggressive and steering precision was critical. The harrow also
showed possibilities but there is a risk of lettuce plants being uprooted when the soil and plant pots
are dry. There were more possibilities with the new equipment in leek as compared to lettuce.
The trials in onions showed that there are possibilities in this crop too. The new equipment
could be used from the second leave stage of the onions onwards. Two or three treatments could be
carried out. In 2000, the onions emerged very quickly. The results of the trial were very hopeful.
98
Intra-row weed control ranged from 36% until 71% (Table 2). Crop damage never resulted in yield
losses above 10 %. The second year, half of the onions emerged quick and the other half after one
week. In spite of this, weed control effects were good. However, plant loss and yield reduction was
a little bit higher than in 2000.
The three sugar beets trials showed that, the new equipment provided possibilities from the 4-6
leave stage onwards. Intra-row weed control after two treatments ranged from 30% until 88%
(Table 2). Loss of sugar beet plants ranged from 0 until 19 %. This plant reduction hardly affected
crop yield.
Discussion
The trails in the different crops on different soil types demonstrated opportunities. In planted
crops, there were more possibilities than in seeded crops. In planted crops, the crop plants have an
advanced growth stage relative to the weeds. Trials made clear that when the weed plants are small
they could be killed easily. When the weed plants are larger, it is more difficult. It is there where the
new equipment can be an improvement. Further improvements should aim at increased selectivity
or a wider range of environmental conditions in which the equipment can be successfully used.
Fingerweeders together with the torsionweeders proved to be more selective to especially
broad-leaved crops than harrows. Another advantage of the fingerweeder is that it appears to move
uprooted weed plants from the crop row. There are at this moment many different types: a small one
(for a row distance from about 20 cm), the normal one (with rubber fingers) and the new ones from
synthetic material of varying flexibility.
One of the problems of the fingerweeder was the effectivity on firm soil, as the fingers could
not get into the soil. The new ones seemed to offer more possibilities, but additional tests are
required.
Torsionweeders can been used in planted crops more effectively than in sown crops. In planted
crops, tine tips can be crossed 5 cm without crop damage. Tines should be tilted about 30°
backwards into the soil. In sown crops, it is very important that the tines are very precisely steered
and in a young crop, the tine tips should be spaced a little. When heavy clay soils are dry, it is
difficult to get the tines in the soil.
The rotor harrow can be used in many crops. It worked better on clay soils than on sandy soils.
On sandy soils, the tines do not stir the soil enough. This tool was designed to work on heavy soils:
the tines penetrate the soil better and weed and soil parts are being thrown out of the row. However,
there is a higher probability of crop plant losses.
The powered harrow was especially developed for planted leek. The tines go through the crop
row transversely. They could remove bigger weeds than the most other machinery. However,
selectivity in other crops appeared to be lower, but more research is still needed.
99
Table 1. Percentage weed control after using different machinery in iceberg lettuce and leek (PPO
average of 1998 and 1999 in Horst (sand) and Lelystad (clay))
Iceberg lettuce
hoeing and harrowing
hoeing and fingerweeder
hoeing and torsionweeder
chemical
*
Leek
Clay
73*
88
86
63
Sand
92
97
86
96
clay
84
90
88
96
sand
90
93
92
99
In 1998, harrowing was impossible and only the hoe was used.
Table 2. Weed control results: % intra-row weed control in sugar beets (10- cm wide zone) and
onions (6-cm wide zone)
sugar beet
2000 sand `
2001 sand
onion
2001 clay
2000
hoeing + small fingerweeder
hoeing + normal fingerweerder
64 b
hoeing + fingerbrushweeder
35
hoeing + torsionweeder
hoeing+torsionw.+fingerweeder
47
b
c
36
b
56
b
50
b
44
b
71
c
46
b
54
b
55
b
37
c
69
32
b *
62
bc
41
c
88
38
b *
45
b
hoeing + rotor harrow
de
48
38
c
3
bc
73
c
a
63
bc
hoeing
Chemical
bc
bc
hoeing + powered harrow
hoeing + harrow
62
65
cd
0 a
81 a
97
e
95
2001
*
0 a
d
90
0 a
e
96
c
* = One weeding
Table 3. Percentage of crop plant reduction
sugar beet
2000 sand
2001 sand
onion
2001 clay
2001
5.9
9.3
12.0
4.2
1.0
3.3
15.0
3.5
0
1.4
6.8
2.3
2.8
5.6
*
5.7
5.0
3.2
*
hoeing + harrow
3.5
18.6
19.5
0
0
hoeing
chemical
= One weeding
*
8.2
19.6
5.2
*
2000
2.0
2.6
18.8
0
4.1
5.5
1.6
4.9
3.0
100
Table 4. Relative crop yield (%) of sugar beet and onion
sugar beet
crop yield chemical ton/ha =100
onion
2000 sand
2001 sand
2001 clay
2000
2001
16.8 sugar
13.8 sugar
13.3 sugar
89.2
63.6
100
93
97
96
95
91
95
100
101
94
100
96
94
96
94
100
95
96
95
97
hoeing + harrow
99
91
92
91
96
hoeing
chemical
100
100
94
94
106
97
100
100
100
101
An experimental study of lateral positional accuracy achieved during
inter-row cultivation.
M C W Home1, N D Tillett1, T Hague1, R J Godwin2
1
Silsoe Research Institute, Bedfordshire, England
2
Cranfield University at Silsoe, Bedfordshire, England
Abstract
In order to ascertain the lateral positioning accuracy achieved during inter-row cultivation six
different inter-row hoeing systems were evaluated. Systems tested included front and rear
mounting, tractor driver guidance, second operator guidance and automatic computer vision
guidance. Their performance was evaluated using an adaptable evaluation rig that enabled the true
hoe path and forward speed to be recorded.
Analysis of the results has shown that an additional guidance system improves the lateral accuracy
in hoeing operations and that an automatic vision guidance system provides the most accurate
control giving a standard deviation of 9mm with a bias of –7 mm travelling at a speed of 6.5 kph.
The vision guidance system also provides effective control at forward speeds of 11 kph, which
offers the prospect of reducing costs by enabling more area to be covered in the number of
workable days available.
The reliance on driver ability to achieve a good hoeing performance substantially reduced when a
vision guidance system was used.
Establishment of lateral positioning data provides the opportunity to maximise weed kill and
minimise crop damage by optimising inter-row cultivated width. In an example taken from our
results, optimising the width of the hoe blade between the crop rows provided 13% extra weed kill.
Introduction
Up until half a century ago, inter-row weed control was carried out by hand and animal drawn
implements. In motorised agriculture mechanical inter-row weed control was largely replaced by
chemical weed control (Kouwenhoven,1994). However, in recent times, with a market demand for
organic farming and a greater awareness of environmental damage caused by chemical application,
there has been a shift back towards mechanical methods in a mechanised farming system.
Inter-row hoes operate between the crop rows and are generally effective against a wide range
of weed species at a range of growth stages. Accurately guiding a mechanical inter-row hoe
between crop rows demands high concentration as deviation from the centre-line results in crop
damage, (Home et al 2001)
This experimental study compares some of the manual and automatic guidance techniques
available for inter-row cultivation and establishes performance data in terms of lateral accuracy for
best practice. We discuss how this information is essential to optimise implement configuration and
how this might aid developments in intra-row weed control. The benefits that automatic guidance
can offer are also discussed.
102
Methods and materials
The experiments and experimental apparatus detailed in this paper were designed to record the
true hoe path of mechanical inter-row hoes whilst operating under actual field conditions. To
ascertain the lateral positioning of six hoeing systems an adaptable evaluation system was
developed. Evaluation consisted of leaving a trace of dye on the ground to record the path taken by
the hoe blades in normal operation. The position of that dye trace relative to the crop rows could
then be measured manually.
The apparatus to deliver the dye trace is shown in Fig 1 mounted on a 4m inter-row hoe. The
main components of the system are the pressure vessel containing vegetable dye, a solenoid valve
and a control circuit.
Figure 1. Lateral position monitoring system fitted to an inter-row hoe
The evaluation of each hoe was undertaken on commercial crops, therefore a vegetable based
dye trace was chosen to eliminate any harmful contamination.
The solenoid and jetting nozzle are mounted 200 mm directly behind a hoe tine and 60mm
above the soil surface. The distance behind the hoe tine allows soil to settle after being hoed, thus
leaving a visible dye trace on the surface. The dye is delivered to the nozzle at a pressure of 2 bar
via the solenoid valve from the hand primed pressure vessel.
Activation of the system is by a remote radio link ensuring that the driver is unaware of
precisely when monitoring is being undertaken, thus reducing the effect of unsustainable increases
in concentration. Upon activating the control circuit, vegetable dye is pulsed from the jetting nozzle
for 0.5 seconds per second. The dye pulses enable true forward speed to be calculated by measuring
the length of dye trace on the ground. True hoe path is recorded by measuring the dye trace in
103
relation to a number of crop rows using a template marked with the row crop spacing, a technique
detailed by (Tillett et al.,1999).
Table 1 summarises the evaluations, in each case hoes were mounted to a traditional three-point
linkage arrangement on the tractor. The 3 m fixed hoe (Run A) was the only hoe to be front
mounted, all the others were mounted at the rear. All hoes except the 4m fixed hoe used in Run C
and identified with an asterix in Table 1 had tight check chains to ensure the lower link arms did not
move independently of the tractor, thus ensuring the hoe frame closely followed tractor position.
Table 1. Mechanical hoes under evaluation
Run
Hoe type
Steerage
System
A
3m fixed hoe
Tractor driver
B
9m steerage hoe
Second operator
C
4m fixed hoe*
Tractor driver
D
4m steerage hoe
Vision guidance
E
4m fixed hoe
Tractor driver
F
4m steerage hoe
Vision guidance
* Hoe mounted with slack check chains
Operator (s)
Mounting
Crop Type
Professional
Professionals
Professional
Non-professional
Non-professional
Non-professional
Front
Rear
Rear
Rear
Rear
Rear
Wheat
Sugar beet
Wheat
Wheat
Wheat
Wheat
Three out of the six evaluations relied entirely on the driver’s vision to guide the hoe accurately
between crop rows. The other three trials involved steerage hoes that used a hydraulically operated
lateral side shifting mechanism to make fine adjustments between a fixed frame on the tractor and a
moving frame to which the hoe blades were attached.
Lateral movement of the 9m sugar beet steerage hoe (Run B) occurs through a second operator,
who is located at one side of the hoe in a purpose built cabin, mounted onto the moving frame of the
hoe. This second operator has a clear view of the crop rows ahead and controls a hydraulic orbital
control valve. The control valve operates two hydraulic linear actuators that facilitate lateral
movement between the fixed head stock and rear frame. A pointer mounted directly in front of the
additional cab aids alignment with the crop rows. The tractor driver still has responsibility for
aligning the tractor with the row, and the additional driver corrects/dampens any driver error
resulting in hoe misalignment. Figure 2 shows the 9 m steerage hoe.
The remaining two trials (Runs D and E) used a vision guidance system developed at Silsoe
Research Institute and now sold by Garford Farm Machinery under the name Robocrop. The hoe
evaluated in this study used a pre-commercial system, as shown in Fig 3, but one that was very
similar to the commercially available version. It consisted of two frames, the front frame was
connected to the tractor via the 3-point linkage with check chains tight. Two flanged wheels
mounted on the fixed frame provided further resistance to lateral movement. The rear frame was
linked, via a parallel linkage, to the front frame allowing it +/- 15 cm of sideways movement
controlled by hydraulic actuators. Single mounted spring tines with 13 cm wide A-blades were
arranged to cultivate in between the winter wheat cereal rows at 22 cm spacing along the moving
frame. A video camera was mounted on the moving frame inclined down at 45o such that it viewed
five crop rows to one side of the tractor as illustrated in Fig 4. Images were passed at 25 Hz to a
200 MHZ Pentium PC and analysed to extract the lateral offset and heading angle of the camera
with respect to all five crop rows. The analysis techniques employed (Tillett & Hague, 1999;
Hague & Tillett 2001) were robust to moderate levels of missing crop and weed growth.
Figure 2. 9m steerage hoe in sugar beet
Figure 3. Experimental vision guided cereal hoe
104
105
Figure 4. View from vision guided hoe camera showing correctly located crop rows even in the
presence of partial shadow in the image region.
With one exception all experimental runs were conducted at speeds regarded as appropriate for
the crop and soil conditions present at the time of the trial. That exception was the vision guided
run (Run F) conducted at 11 kph. This trial was conducted specifically to test previous experience
suggesting vision guidance could perform without loss of accuracy at speeds in excess of normal
cultivation limits or those that could be sustained manually for extended periods. The wheat crop
chosen for this trial was hoed when the flag leaf was just visible [decimal code growth stage 37,
(Tottman & Broad,1987)] and was sufficiently robust to withstand the amount of soil movement
created at this elevated speed.
During each run a minimum sample size of 30 dye traces were recorded to ensure a
representative measure of the lateral positioning. This was repeated several times across and
throughout the field, to ensure the samples were random. All of the individual data sets from each
run were collated, from which the standard deviation and bias were calculated.
Results
A summary of the results presented graphically in Fig 5 shows that in general it is not
unreasonable to approximate the distribution of lateral errors to normal. Table 2 therefore
characterises error distributions measured from each trial in terms of their mean errors and standard
deviation about that mean.
Automatic vision guidance (Run D) provided the most accurate control with a standard
deviation of 9 mm and a bias of –7mm operating at a speed 6.5 kph. The results also confirmed
that vision guided performance was not greatly effected by speed as Run F at 11kph achieved very
similar performance figures.
A direct comparison of Runs D and E (manual and vision guided 4m hoe at 6.5 kph) were
undertaken with the same tractor, hoe and (non-professional) driver to ascertain differing lateral
accuracy. The guidance system was locked centrally for the tractor driver guided run. Results
show that vision guidance brought standard deviation down from 14 mm to 9 mm and bias down
from –17 mm to –7 mm.
106
Relative Frequency
3m front mounted hoe at 4.5 kph
Run A (Tractor Driver)
9m Steerage hoe at 4.8 kph
Run B (Second operator)
4m fixed hoe at 5.1 kph
Run C (Tractor Driver)
4m steerage hoe at 6.5 kph
Run D (Vision guidance)
4 m fixed hoe at 6.5 kph
Run E (Tractor driver)
4m steerage hoe at 11 kph
Run F (Vision guidance)
-60
-40
-20
0
20
40
60
Deviation (mm)
Figure 5. Lateral positioning accuracy of mechanical inter-row hoes
Table 2. Lateral positing accuracy results
Run
A
B
C
D*
E*
F*
Guidance
Tractor driver (Front mounted )
Second operator
Tractor driver
Vision guidance
Tractor driver
Vision guidance
* Non –professional driver
Speed
(kph)
4.5
4.8
5.1
6.5
6.5
11.0
Bias
(mm)
9
-2
7
-7
-17
-8
Standard
Deviation (sd)
22 mm
10 mm
11 mm
9 mm
14 mm
10 mm
Guidance error
95.4% (2 sd)
44 mm
20 mm
22 mm
18 mm
28 mm
20 mm
Comparison between professional and non-professional drivers under manual guidance
indicates, as might be expected, that the former out performed the later though performance was not
as good as the vision guidance system, and was achieved at slower speeds. The front mounted hoe
had the worst performance with a standard deviation of 22 mm. However, it would unreasonable to
assume from one series of results that front mounted hoes have the worst lateral positioning.
Further analysis of front mounted hoes would be required before further conclusions could be made.
107
Discussion
The operators estimated hoeing speed was found to be slower than true measured hoeing speed.
Each operator was asked to drive in their usual manner, but there is no way of judging whether they
tried to excel by increasing concentration, or in fact they under performed due to the increased
pressure they may have felt from being monitored. Remote monitoring via the radio link meant
drivers were unaware exactly when they were being monitored and so it is hoped that performance
was representative of normal hoeing conditions. Drivers were asked if they would feel comfortable
operating at higher speeds and their replies were all the same in that increased speed would be to the
detriment of the crop.
The vision guided hoe (Run F) enabled high speed hoeing (11 kph) to take place without loss of
accuracy. One reason for this may have been that it was noticeable that there were fewer driving
steerage corrections made at higher speeds. Such corrections are not measured by the control
system and therefore represent a performance degrading disturbance. A reduction in these operator
induced disturbances may balance negative factors such as the increased significance of control
time delays as speed increases. Paarlberg et al (1998) reported that higher speed cultivation could
improve the odds of timely completion of needed cultivation, and that faster speed did not impede
weed control or yield in corn. If the pre-mentioned is accepted, then by increasing the forward
speed of a 4m hoe from 6.5 kph to 11 kph changes the work-rate of the hoe from 1.95 ha/hr to 3.3
ha/hr respectively accounting for a field efficiency of 75%. Over an eight-hour day the high-speed
hoe would cover an extra 10.8 hectares, thus substantially lowering the cost of that operation.
One of the major uncertainties relating to mechanical weed control is the number of workable
days available. With timelines of operation being critical, high speed hoeing may be advantageous.
In recent years the number of available workable days in the UK has reduced due to the wetter
climate in autumn and spring, if this climatic change continues then high speed hoeing may well be
a solution.
Melander and Hartvig in 1997 reported that inaccurate steering becomes much more important
the closer the shares get to the crop, therefore hoeing close to the crop requires accurate and reliable
steering of the hoe. The six evaluations undertaken have highlighted the variability in lateral hoe
position and inherent positioning bias in the hoeing operation. Improving the lateral positioning
accuracy of the hoes will enable the hoe blade width to be optimised, maximising weed kill by
increasing cultivated area within the row, whilst keeping crop damage levels low.
The factors that affect blade optimisation, are illustrated in Fig 6, they are root zone clearance,
guidance error and positioning bias. These three factors are critical when attempting to optimise the
blade width.
The crop zone is left unhoed to ensure that minimal root damage occurs, which could result in
reduced yield. Guidance error made up of bias and variability (represented in terms of standard
deviation) result in a need to reduce blade width, therefore comparisons of different guidance
techniques can be made by investigating the percentage increase in cultivated area between the crop
by having improved lateral positioning of the hoe.
108
RW
Key
CZ
RW = Row width
HW = Hoe blade Width
CZ = Crop Zone
V = Error due to Variability
(V = 2 * S.D.)
B = Error due to Bias
Hoe Blade
HW
V
B
V
Figure 6. Hoe blade optimisation
The generic formula below calculates the percentage hoed area accounting for the prementioned variables. Hoe blade width has been calculated on the basis that variability in hoe blade
position over the long term bias, is equal to twice the standard deviation. This ensures that 95.4% of
the time no crop damage occurs.
HW
RW [ B CZ (2 u V )]
% Hoed area
HW
u 100
RW CZ
It should be noted that a direct comparison of the percentage hoed area can only be made if
comparing two systems on the same crop spacing.
An example of the advantages that improved lateral positioning has on hoed area is calculated
below.
Runs D and E are compared as all the variables were the same apart from the guidance of the
hoe, run D having vision guidance and run E having no guidance.
109
Table 3. Blade width optimisation
Factors
Row spacing
Crop zone
Error due to Bias
Error due to Variability
Run D
220 mm
20 mm
7 mm
18 mm
Run E
220 mm
20 mm
17 mm
28 mm
The optimised hoe width for Runs D and E using the Hoe width formula follow: Run D = HW
220 [7 20 (2 u18 )] 157 mm
Run E = HW
220 [17 20 (2 u 28 )] 127 mm
Run D % Hoed area
157
u 100 78.5%
220 20
Run E % Hoed area
127
u 100 63.5%
220 20
Kouwenhoven, 1994 states that with inter-row weed control 60-70% of the surface is treated,
and also states that with guidance this may be about 80%. The above calculation supports this view.
Hoe width optimisation by utilising machine vision is an appropriate method of achieving
greater weed control and increases weed kill. The result above shows that a 15% increase in
cultivated area can be achieved. Jones & Blair (1996) indicate that cutting and burial will
approximately kill 85% of the weeds, therefore it can be assumed that a 13% increase in weed kill
per unit area could be achieved by optimising blade width.
By having a guidance system fitted to a mechanical inter-row hoe, the lateral performance of
the hoe will be improved. The assurance of knowing that the hoe is being guided by an additional
system other than purely the driver alone will reduce the pressure on the operator and enable hoeing
at higher speeds. The operator can also concentrate more on checking the hoe is cultivating
correctly and examine the crop throughout the field.
Lateral positioning data is useful in the design of inter-row cultivation systems for weed control
between crop rows as outlined above. However, the data is also of potential benefit in designing
systems to deal with weeds in-the-row. This might be achieved by burial through controlled soil
throw into the row, or by positioning devices such as finger weeders over the row. More
ambitiously in crops such as brasicas, grown at wide spacing in the row, it might be possible to
operate devices on a cyclical manner so as to disturb weeds in the row leaving the crop untouched.
Data on the accuracy of inter-row positioning is an important starting point in assessing practical
approaches to in-the-row weed control devices that will form part of the authors future work.
110
Conclusions
x
x
x
x
x
x
Guidance systems for inter-row hoes whether using computer vision or an additional operator
enabled improved accuracy compared to unguided hoes.
Automatic vision guidance systems offer increased consistency of performance over long
periods without operator fatigue, whilst maintaining high levels of accuracy.
Driver ability affects lateral positioning of the hoe, but with vision guidance driver accuracy is
not a key requirement.
Greater forward speeds can be achieved with vision guidance providing accurate control that
could not be achieved with conventional fixed inter-row hoes.
Knowledge of achieved accuracy enables blade width to be optimised, increasing weed kill as
the hoe can be safely guided closer to the crop.
Lateral positioning data provides the essential information for the future development of an
intra-row weeder.
Acknowledgements
We would like thank EPSRC and Douglas Bomford Trust for funding this work, Garford Farm
Machinery and Robydome Electronics for equipment loan. We also acknowledge Mr R. Steele, Mr
F Oldfield, Mr N. Watts for allowing field monitoring and the support of colleagues at Silsoe
Research Institute and Cranfield University – Silsoe.
References
HAGUE, T. AND TILLETT, N. D. (2001) A bandpass filter approach to crop row location and
tracking. Mechatronics 11(1), 1-12.
HOME M C W; TILLETT N D; GODWIN R J (2001). What lateral position accuracy is required
for weed control by inter-row cultivation?, Proceedings of the BCPC Conference – Weeds
2001, 1: 325-328
JONES P.A.; BLAIR A.M. 1995 The effect of different types of physical damage to four weed
species, Proceedings of British Crop Protection Conference – Weeds 1995
KOUWENHOVEN J K (1994), Some possibilities of Post-drilling mechanical weed control.
Engineering for Reducing Pesticide Consumption & operator Hazards, Acta Horticulturae
372.
MELANDER B; HARTVIG P. (1997) Yield responses of weed free seeded onions [Allium cepa] to
hoeing close to the row, Crop Protection 16: pp 687-691
PAARLBERG K R; HANNA H M; ERBACH D C; HARTZLER R G (1998). Cultivator Design
for Interrow Weed Control in No-till Corn, American Society of Agricultural Engineers 14(4):
353-361
TILLETT N D; HAGUE T; BLAIR A M; JONES P A; INGLE R; ORSON J H (1999), Precision
inter-row weeding in
winter wheat. Proceedings of the BCPC Conference – Weeds 1999,
2: 975-980
TILLETT N D; HAGUE T; (1999) Computer based hoe guidance for cereals – an initial trial,
Journal of Agricultural Engineering Research 74 225-236
TOTTMAN D R; BROAD H (1987) Decimal code for the growth stage of cereals. The annals of
Applied Biology 110 683-687
111
Weed control by a rolling cultivator in potatoes
Karsten Rasmussen
Danish Institute of Agricultural Sciences
Department of Crop Protection
Research Centre Flakkebjerg, DK-4200 Slagelse
Tlf.: + 45 5811 3399
Fax: + 45 5811 3301
E-mail: Karsten.Rasmussen@agrsci.dk
Abstract
A new project has been started in 2000 to optimise the efficiency of the rolling cultivator for
weed control in potatoes. The objective is to minimise the number of treatments and the crop
damage and to maximise the control effect on annual and perennial weeds. On a loamy soil, a
tolerance (weed-free) and an efficiency experiment were conducted with 0, 2, 3 and 6 passes with
the rolling cultivator. On a sandy soil, an efficiency experiment was conducted with 0, 1, 2 and 4
passes with the rolling cultivator and a herbicide treatment. The timing was approximately intervals
of one week (pre-emerged weeds), two weeks (cotylodon-stage weeds) and three weeks (true-leafstage weeds) with the large intervals at the few passes. The effects on weed biomass of annual
weeds were on both locations above 80%, even with one or two passes. The timing was adjusted to
the weed size, but the efficiency seemed to be rather independent of the weed size. The efficiency
was also independent of the species of the annual weeds. The perennial weeds Elymus repens L. and
Cirsium arvense (L) Scop were less efficiently controlled, but still above a 50% reduction in weed
biomass. Increasing the number of passes increased the efficiency to above 75%, but regrowth
continued. The yield response was negative (-10 %) on the coarse sand soil and positive (+10 %) on
the sandy loam soil compared with herbicides. The recommended speed is 10 to 12 km/h, which
indicate a very high field capacity of the tool. The disadvantages are that it is difficult to adjust the
implement without experience and that it hardly can keep the ridge size that is desirable.
Introduction
Focus on mechanical weed control in conventional potato production in Denmark has been
intensified because of a general interest in reduction of the total use of pesticides. Potato is one of
the most intensive sprayed agricultural crops in Denmark, mainly due to intensive spraying against
potato late blight (Phytopthora infestans) and weeds. It has been decided to reduce the total number
of sprayings by normal dosage per crop (‘Treatment Index’) in Denmark. Practical experiences
indicate that mechanical weed control is an alternative to herbicide spraying, but few relevant
experiments have been found in the literature.
In England, 3 years’ experiments with 1, 2 or 3 passes were conducted (Kilpatrick, 1995). One
pass caused 59-87% reduction in weed biomass, two passes 85-87% reduction and three passes 70%
reduction. The effects of herbicides were above 87%. The yield response depended on the weed
pressure i.e. at a low weed pressure weed control reduced the yield, and at high weed pressures the
yield increased. There were no major differences between yield response to chemical and
mechanical weed control.
In two years with low weed pressure, experiments in the USA showed similar effects on weed
biomass and yield of herbicides and ridging plus two times cultivation by a rolling cultivator
112
(Eberlein et al., 1997). In a third year with high weed pressure, the effect of mechanical weed
control (61%) was lower than the effect of herbicides (99%). This year the yield in mechanical
controlled plots was reduced by 12% compared with herbicide controlled plots, but the difference
was not significant.
In Schweitzerland, experience showed a 6% higher yield by three treatments with rolling
cultivation compared to herbicides (Irla, 1995). Weeds were not measured, but the economy was
significantly improved by the mechanical strategy.
The general impression is that, at moderate weed pressures weeds could be controlled as
efficiently by rolling cultivators as by herbicides, without yield reductions. At high weed pressures,
efficient mechanical weed control was more difficult, and a reduction in yield was seen due to crop
damage or competition from surviving weeds was seen.
To gain more experience it was decided to start field experiments in Denmark with the
objective of developing cost-effective strategies for non-chemical weed control in potatoes. The aim
is to minimise the number of treatments and the crop damage and to maximise the control effect on
annual and perennial weeds by the right timing. The experiments continue in 2002.
Material & methods
Experiments were conducted on sandy loam (Research Centre Flakkebjerg) without irrigation
and one on coarse sand soil (Jyndevad Experimental Station) with irrigation in 2001. On the loamy
soil a tolerance (weed free) and an efficiency experiment were conducted with 0, 2, 3 and 6 passes
with the rolling cultivator. On the sandy soil, an efficiency experiment was conducted with 0, 1, 2
and 4 passes with the rolling cultivator and a herbicide treatment. Dates of treatments are seen in
Table I. The timing was approximately intervals of one week (pre-emerged weeds), two weeks
(cotylodon-stage weeds) and three weeks (true-leaf-stage weeds) with the large intervals at the few
passes. The parcels in Flakkebjerg were 25 m long with two rows and 1.5 m bare soil between
parcels – 15 m of two rows was harvested. The parcels in Jyndevad were 21 m long with four rows
- 16.7 m of two rows was harvested. Row distance was 75 cm, and there were four replications at
both locations. The rolling cultivator or Lelliston rotary weeder was trademark ’SAMKA’ at both
locations (Fig. 1). Adjustment of the tool is complicated and, experience is important. Basic advises
are:
x The spider gangs have to be adjusted to follow the ridges (same angle) and to cultivate the outer
3-5 cm of the soil.
x Before crop emergence, the top of the ridge has to be cultivated.
x After crop emergence, the spider gangs are moved away from the top, but soil is still thrown
onto the top of the ridges.
The speed was between 7 and 12 km/h depending on the circumstances.
Table 1. Treatments and dates of treatments at the two locations.
Treatmernt
Flakkebjerg
Planting
3.5
Ridging
7.5
Crop emergence
22.5
Strategy 1 (control)
Strategy 2 (true-leaf-stage)
25.5 – 15.6
Strategy 3 (cotylodon-stage)
21.5 - 25.5 – 8.6
Strategy 4 (pre-emerged)
14.5 – 21.5 – 25.5 – 1.6 - 8.6 – 15.6
Herbicide
25.5 – 21.6*1
Weed registrations
21.7
3.9 (mechanical)
Wine kill
Harvest
12.10
113
Jyndevad
19.4
19.4
20.5
16.5
11.5 – 30.5
1.5 – 10.5 – 16.5 – 30.5
17.5 – 28.5*2
23.7
1.10 (natural)
10.10
*1 25.5: Metribuzin 140 g a.i.ha-1 (Sencor, Bayer A/S)
21.6: Rimsulfuron 7.5 g a.i. ha-1 (Titus, Du Pont)
2
* 17/5: Metribuzin 140 g a.i.ha-1 (Sencor, Bayer A/S) & Linuron 550 g a.i.ha-1 (Afalon disp. Avensis)
28/5: Metribuzin 105 g a.i.ha-1 (Sencor, Bayer A/S) & Rimsulfuron 7.5 g a.i. ha-1 (Titus, Du Pont)
Figure 1. Spider gangs at the SAMKA rolling cultivator
Data analyses were carried out using the method of maximum likelihood by the Mixed Linear
Model procedure in SAS (version 6.12, SAS Institute, Cary, NC, USA). An analysis of the residuals
showed that a logarithmic transformation of the data was required to stabilise the variance.
Results & Discussion
The weed flora was very similar at the two locations apart from the perennial weeds in
Flakkebjerg (Table 2 & 3). The effects on annual weeds are very high and consistent at both
locations. One or two passes controlled 80 % of all the present annual weed species (both number
and biomass). As in previous experiments (Eberlein et al., 1997; Kilpatrick, 1995), the effects are
comparable to herbicide treatments – at least surviving weeds have no significant influence on the
yield. The effects on weed biomass are slightly higher than the effects on the weed density, which
indicates smaller plants after cultivation. An explanation might be that the cultivation stimulates
new weed seeds to germinate, but weeds germinated after the last treatment have no competitive
importance.
114
Table 2. Biomass and density of weeds and effect of treatments on sandy loam in Flakkebjerg.
Significant difference from control: NS = Non Significant; * : P < 0.05%; ** P < 0.01;
*** P < 0.001.
Weed species
Treatment
Biomass
Density
-2
Polygonum convolvulus L. Untreated control
62.6 g m
35.8 plants m-2
2 x cultivation
-82 % *
-81 % **
3 x cultivation
-97 % ***
-84 % **
6 x cultivation
-99 % ***
-92 % **
Untreated control
2 x cultivation
3 x cultivation
6 x cultivation
238.7 g m-2
-93 % **
-98 % ***
-100 % ***
31.9 plants m-2
-92 % ***
-100 % ***
-100 % ***
Other weeds
Untreated control
2 x cultivation
3 x cultivation
6 x cultivation
39.6 g m-2
-97 % ***
-99 % ***
-100 %***
52.0 plants m-2
-95 % ***
-95 % **
-89 % **
Elymus repens (L.)
Untreated control
2 x cultivation
3 x cultivation
6 x cultivation
7.6 g m-2
-50 % NS
-85 % **
-84 % *
13.1 shoots m-2
-24 % NS
-63 % *
-52 % NS
Cirsium arvénse (L.) Scop. Untreated control
2 x cultivation
3 x cultivation
6 x cultivation
52.4 g m-2
-62 % NS
-63 % NS
-76 % NS
10,0 shoots m-2
-2 % NS
-11 % NS
-16 % NS
Total
400.9 g m-2
-87 %
-93 %
-96 %
142.8 plants/shoots m-2
-78 %
-84 %
-84 %
Untreated control
2 x cultivation
3 x cultivation
6 x cultivation
115
Table 3. Biomass and density of weeds and effect of treatments on coarse sand in Jyndevad.
Significant difference from control: NS = Non Significant; * : P < 0.05%; ** P < 0.01;
*** P < 0.001.
Weed species
Treatment
Biomass
Density
-2
Polygonum convolvulus L. Untreated control
63.0 g m
28.3 plants m-2
Herbicide
-100 % ***
-100 % ***
1 x cultivation
-96 % ***
-86 % **
2 x cultivation
-93 % **
-82 % **
4 x cultivation
-99 % ***
-96 % **
Untreated control
Herbicide
1 x cultivation
2 x cultivation
4 x cultivation
187.8 g m-2
-100 % ***
-97 % ***
-100 % ***
-100 % ***
31.9 plants m-2
-100 % ***
-97 % ***
-94 % ***
-100 % ***
Stellaria media L.
Untreated control
Herbicide
1 x cultivation
2 x cultivation
4 x cultivation
17.1 g m-2
100 % ***
-100 % ***
-100 % ***
-99 % ***
17,0 plants m-2
-100 % ***
-100 % ***
-94 % ***
-90 % ***
Other weeds
Untreated control
Herbicide
1 x cultivation
2 x cultivation
4 x cultivation
81.3 g m-2
-99 % ***
-98 % ***
-95 % ***
-97 %***
55.0 plants m-2
96 % ***
-90 % ***
-81 % **
-93 % ***
Total
Untreated control
Herbicide
1 x cultivation
2 x cultivation
4 x cultivation
349.2 g m-2
-100 % ***
-97 % ***
-97 % ***
-99 % ***
132.3 plants m-2
-98 % ***
-90 % ***
-86 % ***
-95 % ***
The effects on biomass of perennial weeds (Elymus repens L. & Cirsium arvénse (L.) Scop)
were remarkable but often not significant due to heterogeneous distribution in the field (Table 2).
When looking at the implement, while it was working, it was amazing to see shoots being pulled
out of the soil from up to 15 cm depth. The treatment did not kill these weeds, but regrowth was
delayed, and several repeated treatments might be necessary to have high effects. In an unpublished
Swedish experiment the biomass of Elymus repens roots was reduced by 97 % after two treatments
with the rolling cultivator (Wagner, 1995). These experiences provide perspectives of a unique
method to control both annual and perennial weeds without chemicals.
In the tolerance experiment (herbicide treated) at the loamy soil in Flakkebjerg, two and three
cultivations increased the yield by 10 % compared with both the control and six times cultivation
(Table 4). Here the results indicate a stimulation of the crop growth by cultivation, but by six times
cultivation crop damage is possible. In the weedy efficiency experiment at the loamy soil, three and
six cultivations increased the yield compared with the control and two cultivations (Table 4).
116
Reduced control effects on Elymus repens and Polygonum convolvulus L (Table 2) mainly caused
the yield difference between two and three cultivations.
The yield responses to the mechanical weed control were reduced around 10 %, compared with
the chemical weed control on the coarse sand soil in Jyndevad (Table 5). The intensity of
mechanical weed control did not influence the yield, which indicates that the reduction was not due
to mechanical crop damage. Plausible explanations are that the cultivation reduced the original
ridge size or that the cultivation influences nutrient and water utilisation on this soil type. In next
years’ experiments, we will finish the cultivations by a ridging to rebuild the original ridge size.
The strategies for weed control were related to the weed size. The intervals between the
cultivations turned out to be approximately 3, 2 and 1 week for strategy 1, 2 and 3 (Table 1). The
experience was that the control effects were rather independent of the weed size (Fig. 3, 4, 5). Even
large weed plants were easily controlled, and timing does not have to be related to the weed size.
Instead timing should be related to the crop. Before crop emergence, cultivation was done by
overlap of the spider gangs. After crop emergence the spider gangs were adjusted away from the top
of the ridges to prevent crop damage. This implement control the weeds both by uprooting and soil
covering in one operation, but weeds emerged on the top of the ridge after the crop were only
controlled by soil covering. This is not as efficient as up-rooting (Kurstjens & Kropff, 2001), and it
was notable that most of the surviving weeds in the experiments were growing on the top of the
ridges.
Figure 3. Highly infested field in Jyndevad (outside experiment) before treatment.
Figure 4. Highly infested field in Jyndevad (outside experiment) after treatment.
117
Figure 5. Highly infested field in Jyndevad (outside experiment) one week after treatment.
Table 4. Potato yield at sandy loam in Flakkebjerg. Significant difference from 3 cultivations: NS =
Non Significant; * : P < 0.05%; ** P < 0.01; *** P < 0.001.
Treatment
No herbicides
Plus herbicides (weed free)
1.
2.
3.
4.
0 x cultivation
2 x cultivation
3 x cultivation
6 x cultivation
Mean yield
(ton/ha)
18.5
49.1
56.7
59.0
Relative
effects
33 ***
87 **
100
104 NS
Mean yield
(ton/ha)
40.6
44.8
45.7
41.5
Relative effects
89 **
98 NS
100
91 *
Table 5. Potato yield at coarse sand in Jyndevad. Significant difference from 2 cultivations: NS =
Non Significant; * : P < 0.05%; ** P < 0.01; *** P < 0.001
Treatment
Mean yield
Relative effects
(ton/ha)
1. 0 x cultivation
22.8
41 ***
2. 1 x cultivation
57.8
104 NS
3. 2 x cultivation
55.4
100
4. 4 x cultivation
57.8
104 NS
5. Herbicide
62.6
113 **
As an alternative to herbicides, the economy is very important. Assuming the same control
effects and yields by 2 or 3 cultivations and herbicide treatments, which is realistic, the variable
costs are very similar. The major difference is the investment if the farmer has a sprayer in advance.
Economic calculations can be conducted with several assumptions, but if the implement can be used
on large areas each year, it is seen as an economic alternative to herbicides. The rolling cultivating
is less dependent on weather conditions (wind in Denmark!) than spraying and more days for
control are available. Furthermore, with up to six row implements and driving speeds of 10-12 km/h
the capacity is large. Additional environmental arguments and considerations could be listed as
well.
118
From one years experiments it can be concluded that:
x Effects on annual weeds of mechanical weed control by rolling cultivators are comparable to
herbicide effects.
x More than 50 % effect on perennial weeds was obtained.
x Timing relative to weed size was not important.
x Positive yield responses of cultivation versus herbicides were seen on loamy soil, while
negative responses were seen on sandy soil.
x It is realistic that rolling cultivators can be a cost-efficient alternative to herbicides in Danish
potato production in the near future.
References:
EBERLEIN C V, P E PATTERSON, M J GUTTIERI & J C STARK (1997) Efficacy and
economics of cultivation for weed control in Potato (Solanum tuberosum). Weed Technology
11, 257 – 264.
IRLA E (1995) Pflegetechnik und mechanische Unkrautregulierung in Kartoffeln. FAT-Berichte
462, 1- 8.
KILPATRICK J B (1995) A comparison of agricultural and chemical methods of weed control in
potatoes. In Proceedings 1995: ANPP – Sixteenth columa conference. International meeting on
weed control, Reims. 387 – 394.
KURSTJENS, D A G & M J KROPFF (2001) The impact of uprooting and soil-covering on the
WAGNER D (1995) Kvickrotsbekämpning i potatis. Note from ‘ Hushållningssällskapet i Halland’.
119
Options for mechanical weed control in string bean
– work parameters and crop yield
M. Raffaelli1, P. Bàrberi2, A. Peruzzi1 & M. Ginanni3
D.A.G.A.E., Settore Meccanica Agraria, University of Pisa, Italy; 2Scuola Superiore Sant’Anna,
Pisa, Italy; 3Centro Interdipartimentale di Ricerche Agro-ambientali “E. Avanzi”, S. Piero a Grado,
Pisa, Italy
1
Introduction
The introduction of organic cultivation of many crops is rapidly gaining pace, leading to the
need to devise techniques and equipment to ensure effective non chemical weed control (Bonifazi,
2001).
The increasing emphasis on physical means for integrated and organic weed management is in
line with the mounting public concern for environmental safeguard and the growing consumer
demand for high quality food products (Peruzzi et al., 1995 and 1999; Raffaelli & Peruzzi, 1998)
and is in full agreement with the orientations of the EU agricultural policy in recent years ("Agenda
2000").
In this perspective, a series of purpose-designed operative machines were studied and devised
to perform efficient and economically viable selective and non-selective direct physical (mechanical
and thermal) weed control. Numerous experiences have been carried out on these machines (Kress,
1989; Rasmussen, 1991 and 1992; Böhrnsen, 1993; Peruzzi et al., 1993 and 1995; Melander &
Hartvig, 1995; Ascard & Bellinder, 1996; Kouwenhoven, 1997; Melander, 1997; Fogelberg, 1998
and 1999; Ascard et al., 2000; Bàrberi et al., 2000; Cloutier & Leblanc, 2000; Kurstjens & Bleeker,
2000). Results obtained are often very good, but analysis of data suggests that many factors can
play an important role in determining the outcome of treatments. Machines having completely
different mechanical and operative characteristics are often used on the same crop and/or soil and
this is not always logic and explicable. This suggests that more detailed evaluations are necessary in
order to analyse and fully interpret results. In order to optimise on-field treatments, experiments are
required to allow in-depth analysis of the interactions between machine working parameters and
soil conditions, crop typology and management practices, as well as weed density, developmental
stage and competitiveness (Rasmussen, 1991 and 1992; Peruzzi et al., 1993 and 1995; Søgaard,
1996; Fogelberg & Dock Gustavsson, 1998; Bàrberi et al., 2000; Kurstjens et al., 2000; Raffaelli et
al., 2000).
The present paper reports part of the results of a study aimed to investigate mechanical and
agronomic performances of different weed control options having very different characteristics that
were operated on the same soil and the same crop.
Trials consisted of a spring-tine harrowing experiment comparing different tine adjustments,
and of a hoeing experiment comparing the effects of different machines (a precision hoe plus or
minus a torsion weeder and a PTO-powered rotary hoe). All the implements are 3 m wide. The
experiments were conducted on adjacent fields with the same soil type (Table 1).
120
The spring-tine harrow (Malin) is composed of two small (each 1.5 m wide) modular frames.
Each frame is composed of 6 transverse rows of 8 tines; each tine is 36 cm long and has a diameter
of 0.6 cm. The J-shaped tines, made of special-purpose steel, are composed of a 25 cm long vertical
segment followed by a second shorter segment (11 cm) angled at 135˚ to the first segment towards
the working direction.
The precision hoe, that is manually steered, has sweep and goose-foot shares and can be
implemented with torsion weeders. The PTO-powered rotary hoe is a conventional machine with Lshaped tools.
Trials were conducted in 2000 and 2001 at the Centro Interdipartimentale di Ricerche Agroambientali "E. Avanzi" of the University of Pisa (43°40’ Lat. N, 10°19’ Long. E). A 30 kW 2WD
tractor was used in any experiments. Further details on the experiments are reported by Raffaelli et
al. (2002).
String bean (Phaseolus vulgaris L. cv. Delinel) was grown under irrigation regime according to
the standard cultural practices in the study area (Raffaelli et al., 2002) and sown at a seeding rate of
29.6 seeds m-2 and an inter-row spacing of 75 cm.
Table 1. Soil physical and mechanical characteristics.
Characteristics
Values
2000
Texture (%)
Sand
(%)
Silt
(%)
Clay
(%)
Classification
Liquid limit (LL, %)
Plastic limit (PL, %)
Plasticity index (LL-PL)
Soil water content (%)
Consistency index
Dry bulk density
Cone resistance (0-5 cm)
Ø > 2mm
0.02 < Ø d 2mm
0.002 < Ø d 0.02 mm
Ø d 0.002 mm
ISSS System
-3
kg dm
MPa
2001
0
62
22
16
sandy-loamy
23
13
10
9
1.4
1.3
0.2
8
1.5
1.4
0.8
Immediately prior to the mechanical treatments, percent soil water content, dry bulk density
and penetration resistance were determined. The soil consistency index at the time of harrowing
was calculated on the basis of Atterberg limits and soil water content.
The harrowing experiment included any combinations between four tine adjustments (ranging
from –30° up to +15°, where values represent the angle E between the upper part of the tine and the
perpendicular to the soil surface, Fig. 1) of the spring-tine harrow. The hoeing experiment
compared four different hoeing systems: (1) a PTO-powered rotary hoe, (2) a precision hoe with
sweep and goose-foot shares, (3) a precision hoe (as before) + torsion weeders, (4) a precision hoe
(as before) + torsion weeders operated with the tines crossed.
Several harrowing or hoeing work parameters were measured or calculated for any treatments,
including working depth, speed and capacity; fuel consumption per hectare and hour, drawbar pull,
useful power, direct input and tractor skidding.
121
String bean yield was determined at different times (as soon as the pods were ready for harvest)
by complete harvest of 2 m of crop row selected in the central part of each plot. Data on weeds and
weed control are reported elsewhere (Raffaelli et al., 2002).
Data shown in Table 1 indicate that at harrowing time the soil was in good condition for tillage.
Compared to 2000, in 2001 cone resistance was 4 time higher, and also the consistency index was
higher. This means that in the second year the tilled soil exerted a higher resistance to tine
penetration.
+ JE
D
)
Fig. 1. Shape and possible adjustments of the tines of the spring-tine harrow: D = 135°, -45° d E d
+15°. The arrow indicates the driving direction.
Mechanical and working parameters of the different harrowing and hoeing treatments are
shown in Tables 2 and 3.
In both years, the working depth of the spring-tine harrow increased with tine angle, ranging
from 1.6-2.0 cm in the least aggressive adjustment (-30°) to 3.0-3.1 cm in the most aggressive one
(+15°). Hardness of the soil influenced the working depth, even though mean absolute differences
among treatments between years were small (3 mm). Working depth of the hoes was always
invariable and much higher than that of the harrow; it is worth mentioning that with the precision
hoe it was not possible to work at a shallower soil depth.
Working speed and productivity of the machines differed only slightly between the years.
Values recorded for the spring-tine harrow were always very high (on average ca. 7 km h-1 and 1.8
ha h-1 respectively) and much higher than those recorded for the hoes. Among the latter, the rotary
hoe emerged as the implement with the lower speed and productivity (ca. three times lower than the
spring-tine harrow).
Fuel consumption increased with increasing treatment aggressiveness, with constant and very
low values for the spring-tine harrow and the precision hoe. Compared to the other hoes, use of the
PTO-powered rotary hoe resulted in higher fuel consumption per hour and hectare (due to lower
working speed and productivity), which increased in 2001 because the soil was harder to till.
122
Drawbar pull increased from the least to the most aggressive treatment, but absolute values
were overall very low.
On average, the power needed for operating the harrow and the precision hoe was 3.5 and 2.5
kW respectively, while the PTO-powered rotary hoe needed 12.3 kW in 2000 and 14.3 kW in 2001.
Spring-tine harrowing required a very low direct input, that was not appreciably influenced by
the change in soil conditions between the years. A low energy input was also required by the
precision hoe (with values similar to those of the harrow), but soil conditions seemed to influence
values. Direct input necessary for operating the PTO-powered rotary hoe was considerably (ca. 10
times) higher and was influenced by soil hardness.
In any case, tractor skidding, when present, was always unimportant.
To fully interpret the outcome of this study, parameters that link mechanical and agronomic
results are hereafter presented.
Table 2. Work parameters of spring-tine harrowing performed with different tine adjustments.
Parameter
2000
2001
- 30° -15° 0° +15° mean - 30° -15° 0° +15° mean
Working depth (cm)
2.0 2.4 2.5 3.1 2.5 1.6 2.1 2.2 3.0 2.2
Working speed (km h-1)
7.1 6.8 6.7 6.5 6.8 7.0 6.8 6.7 6.5 6.7
-1
1.8 1.7 1.7 1.7 1.7 1.8 1.7 1.7 1.7 1.7
Working productivity (ha h )
Fuel con. per hour (kg h-1)
0.7 1.2 1.6 1.7 1.3 0.7 1.1 1.5 1.7 1.2
Fuel con. per hectare (kg ha-1)
0.4 0.7 0.9 1.0 0.7 0.4 0.6 0.9 1.0 0.7
Drawbar pull (N)
1000 1800 2340 2630 1940 1000 1700 2180 2590 1867
Useful power (kW)
2.0 3.4 4.4 4.7 3.7 1.9 3.2 4.1 4.7 3.5
-1
Direct input (MJ ha )
17.6 30.8 39.6 44.0 30.8 17.6 26.4 39.6 44.0 30.8
Tractor skidding (%)
1
5
7
9
5
3
6
7
10
6
Table 3. Work parameters of hoeing performed with different technical solutions.
Parameter
2000
2001
PH
PH + TW Rotary hoe
PH
PH + TW Rotary hoe
Working depth (cm)
5.2
5.2
6.0
5.1
5.1
6.0
-1
Working speed (km h )
3.8
3.8
2.4
3.6
3.6
2.4
1.0
1.0
0.6
0.9
0.9
0.6
Working productivity (ha h-1)
-1
Fuel cons. per hour (kg h )
0.9
0.9
4.5
0.9
1.0
5.1
Fuel cons. per hectare (kg ha-1)
0.9
0.9
7.5
1.0
1.1
8.5
Drawbar pull (N)
2360
2500
2480
2740
Useful power (kW)
2.5
2.6
12.3
2.5
2.7
14.3
Direct input (MJ ha-1)
39.6
39.6
337.5
44.0
48.4
382.5
7
7
-1
10
10
-1
PH = precision hoe, PH + TW = precision hoe + torsion weeder.
Table 4 shows that string bean total yield per working hour obtained with spring-tine harrowing
was nearly two- and four-fold those of the precision and rotary hoe respectively.
123
It is also possible to observe that, to produce 1 Mg of string bean yield (fresh weight), 2.3 to 3.4
MJ were needed by harrowing, 2.9 to 5.4 MJ by precision hoeing and 30.7 to 41.0 MJ by PTOpowered rotary hoeing.
Table 4. String bean total yield (fresh weight) per working hour and direct energy input needed to
produce 1 Mg of produce in the different harrowing and hoeing treatments (all the other
cultural practices were kept constant in all treatments).
Treatment
Kg h-1
MJ Mg-1
2000
2001
2000
2001
Spring-tine harrowing:
+15°
24013
17503
3.1
4.3
0°
24307
15181
2.8
4.4
-15°
24778
16900
2.1
2.7
-30°
25670
13747
1.2
2.3
Mean
24692
15833
2.3
3.4
Hoeing:
Precision hoe
Precision hoe + torsion weeder
Rotary hoe
12850
13496
6603
8081
8082
5593
3.1
2.9
30.7
4.9
5.4
41.0
The machines used in this experiments have different working characteristics, as it is clearly
demonstrated by values of the measured parameters. Furthermore, their behaviour usually changes
according to soil conditions. In harder soil, the spring-tine harrow works more shallowly and it is
not possible for the tines to penetrate deeper in the soil. These data highlight the well recognised
operative advantages linked to the use of the spring-tine harrow, such as the high timeliness and
work productivity, and the very low demand for drawbar pull, power and energy. In contrast, by
using the precision or the rotary hoe tillage depth is independent of soil conditions but is set to a
minimum value that cannot be further lowered. Compared to harrowing, soil conditions influence
work productivity and energetic requirement of the hoes to a much greater extent; this is especially
true for the PTO-powered rotary hoe.
Further studies are required to allow in-depth analysis of the interactions between machine
work parameters and soil conditions, weed density and composition, and crop management
practices.
Acknowledgements
We are very grateful to R. Del Sarto, A. Pannocchia, M. Paracone, L. Pulga and S. Toniolo of
the University of Pisa for their precious cooperation in running the experiments.
References
ASCARD J & BELLINDER RRB (1996) Mechanical in-row cultivation in row crops. In:
Proceedings Second International Weed Control Congress, Copenhagen, Denmark, 1121-1126.
ASCARD J, OLSTEDT N & BENGTSSON H (2000) Mechanical weed control using inter-row
cultivation and torsion weeders in vining pea. In: Proceedings 4th EWRS Workshop on Physical
and Cultural Weed Control, Elspeet, 20-22 March, 41.
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BÀRBERI P, SILVESTRI N, PERUZZI A & RAFFAELLI M (2000) Finger-harrowing of durum
BÖHRNSEN A (1993) Several years results about mechanical weeding in cereals. In: Proceedings
4th International Conference I.F.O.A.M., Dijon, 5-9 May, 93-99.
BONIFAZI L (2001) L’alternativa biologica. Terra e Vita 4, 60-61.
CLOUTIER D & LEBLANC ML (2000) Susceptibility of sweet maize (Zea mays L.) to the rotary
hoe: preliminary results. In: Proceedings 4th EWRS Workshop on Physical and Cultural Weed
Control, Elspeet, 20-22 March, 37-39.
FOGELBERG F (1998) Physical weed control – intra-row brush weeding and photocontrol in
carrots (Daucus carota L.). PhD Dissertation, Department of Agricultural Engineering, Swedish
University of Agricultural Sciences, Alnarp.
FOGELBERG F (1999) Night-time soil cultivation and intra-row brush weeding for weed control in
carrots (Daucus carota L.). Biological Agriculture and Horticulture 17, 31-45.
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(Daucus carota) and annual weeds: a basis for selective mechanical weed control. Weed
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KOUWENHOVEN JK (1997) Intra-row mechanical weed control: possibilities and problems. Soil
& Tillage Research 41, 87-104.
KRESS W (1989) La sarchiatrice a spazzole. Demetra 14, 39-41.
KURSTJENS DAG & BLEEKER P (2000) Optimising torsion weeders and finger weeders. In:
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MELANDER B (1997) Optimization of the adjustment of a vertical axis rotary brush weeder for
intra-row weed control in row crops. Journal of Agricultural Engineering Research 68, 39-50.
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Agricoli 5, 29-36.
PERUZZI A, RAFFAELLI M & DI CIOLO S (1999) Tecniche per la produzione di olio di semi di
girasole di alta qualità. In: Proceedings Convegno Nazionale A.I.I.A. – L’innovazione
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weeding harrows: first experimental results. Agricoltura Mediterranea 123, 236-242.
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RAFFAELLI M, PERUZZI A, BÀRBERI P (2000) Spring-tine harrowing in sunflower and
soyabean: results of two-year trials. In: Proceedings 4th EWRS Workshop on Physical and
Cultural Weed Control, Elspeet, 20-22 March, 37-39.
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control in string bean – effects on weeds. In: Proceedings 5th EWRS Workshop on Physical and
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125
Mechanical intra-row weed control in organic onion production
J. Ascard & F. Fogelberg
Swedish University of Agricultural Sciences, Department of Crop Science,
Box 44, SE-230 53 Alnarp, Sweden
E-mail: johan.ascard@vv.slu.se, fredrik.fogelberg@vv.slu.se
Abstract
In organic production of direct-sown onions (Allium cepa), the labour requirement for intra-row
weed control is a major problem. Therefore, many organic growers use onions from sets because it
is easier to cope with the weeds. However, it is desirable to increase production of onions grown
from seed because of the better onion skin quality and storage ability. Transplanting onion plants
grown from seed is one way to combine high skin quality with ease of weed control. The torsion
weeder, consisting of two flexible steel tines on each side of the row, is effective for intra-row weed
control in several crops, but there are few reports of its use in onions.
The objective of this study was to evaluate effective strategies for mechanical intra-row weed
control using the torsion weeder in direct-sown onions and in transplanted onions grown from seed,
in terms of reduction of annual weeds, labour time for hand weeding, yield and quality. So far, two
field experiments have been carried out in Southern Sweden in 2000 and 2001 as part of a three
year study.
In transplanted onions, we evaluated a weed control strategy, using spring tine harrowing one
week after transplanting plus 2-3 row crop cultivations with torsion weeders for in-row cultivation.
The torsion weeders consist of two flexible steel tines on each side of the row, mounted on a row
crop cultivator. The tines were set together with no distance between the tines, and they were used
at two intensities, regulated by the driving speed. This strategy was compared with inter-row
cultivation only and weed harrowing plus inter-row cultivation. In sown onions, we evaluated a
strategy where we used flame weeding at crop emergence plus 2-3 row crop cultivations with
torsion weeders. This was compared with inter-row cultivation only and flame weeding plus interrow cultivation. All treatments were hand weeded and the labour time for hand weeding was
recorded. Weeds were counted in the 10 cm uncultivated strip within the row only.
Generally there were fewer weeds, a lower labour requirement for hand weeding and higher
yields in the transplanted onions than in the sown onions. In transplanted onions, a combination of
one weed harrowing and three subsequent row crop cultivations using the torsion weeder provided
about 90% weed reduction and over 75% labour reduction, compared to using inter-row cultivation
only. A slightly lower weed control effect was obtained when the torsion weeder was driven at a
lower speed. The weed harrowed and intra-row cultivated onion produced marketable yields of 47
and 38 ton/ha for the two years respectively, which was higher than the yield from the onions that
were inter-row cultivated only.
In direct-sown onions, a combination of flame weeding at crop emergence and subsequent row
crop cultivations using the torsion weeder provided about 80% reduction of in-row weeds and about
65% reduction of the labour use for hand weeding, with a higher yield and no quality reduction
compared to using inter-row cultivation only. In the first year’s experiment in sown onions, flame
weeding gave good control but the torsion weeder poor results, but the opposite was true in the
second year.
The results so far clearly demonstrate the importance of creating conditions in which the crop is
always ahead of the weeds, and of carrying out all the treatments at the right time and with proper
adjustment of the equipment, in obtaining successful results.
126
Experiences related to the use of the weeding harrow and of the roll-star
cultivator in Emilia-Romagna for weed control on hard and common wheat,
sunflower and soyabean in organic agriculture
L. Dal Re and A. Innocenti
(Experimental Station M. Marani, Ravenna – Italy)
Introduction
Since 1997 Experimental Station Marani of Ravenna has set itself the aim to support the
spreading of organic farming methods in its own region. In order to achieve this aim, Marani
Station has equipped itself with specific machinery and equipment used to implement experimental
and demonstrative programmes. Weed control is frequently the most difficult problem to work out
in production of organic arable crops in Po Valley and this is why weed harrowing and hoeing were
particularly studied.
Method
Altogether, 20 experimental fields have been implemented in the years 1997-2000. The
methodological choose was to work according to experimental schemes with repeated big plots
(min. 0.5 ha) while using open field machinery and equipment on real-scale surfaces (2-10 ha). This
approach has given us the possibility to obtain interesting results, also transferable in quite a short
time. For the on-farms trials we used several machines: 2 weeding harrow (8 and 6 mm teeth of
diameter) for trials on hard (Triticum durum) and common wheat (Triticum aestivum); 1 spring
tines harrow, 1 weeding harrow; 1 roll-star cultivator for trials on sunflower (Helianthus annuus)
and soyabean (Glycine max).
Results
Hard and common wheat.
The following technique has been developed for the use of the weeding harrow on common
wheat with close row spacing (17-18 cm).
1) A false sowing with “heavy” weeding of the field (teeth weeding harrow 8 mm in
diameter), in autumn; the second weeding and the sowing have been done at the end of
traditional sowings.
2) 3 interventions of “light” weeding, intervening from the 2 leaves stage to the one of end of
shooting, in winter. The speed ranged between 4 and 6 km/hour with 6 mm teeth and
“light” winding up for the first intervention, and then “medium” winding up.
This technique allowed a sufficient weed control both for monocotyledons (Lolium
multiflorum, Alopecurus mysuroides, Avena spp.) and dicotyledons (Papaver rhoeas, Matricaria
camomilla, Sinapis spp, Veronica spp). The yields of common wheat decreased of 8-14 % against
conventional agricultural test while of hard wheat increased of 3-10 %.
127
Sunflower in organic agriculture
The following technique has been developed with regards to sunflower with 45 cm row
spacing. It is based on the use of: flexible tines harrow, weeding harrow and roll-star cultivator.
1) One passing with flexible tines harrow on the frozen and well prepared field, in JanuaryFebruary.
2) One or two false sowings with 8 mm teeth weeding harrow for emergence weeds (germ
formation stage)
3) One delayed sowing at the end of traditional sowings.
4) One weeding with 6 mm teeth with 2 leaves sunflower (weeds at fully developed
cotyledons stage). The speed goes from 3 to 4 km/hour with “light” winding up.
5) One hoeing- earthing up with “roll-star cultivator” with 2-6 leaves sunflower (weeds at the
stage of maximum 2 leaves); the speed goes from 5 to 6 km/hour with an earthing up of 6-8
cm.
This technique allowed a sufficient weed control both for monocotyledons (Lolium
multiflorum, Avena spp.) and dicotyledons (Polygonum aviculare, Chenopodium album,
Polygonum persicaria, Solanum nigrum, Amaranthus retroflexus, Mercurialis annua).
Yields decreased of about 9-18 % against conventional agricultural test.
Soyabean in organic agriculture.
The following technique has been developed for soyabeans with 45 cm row spacing. It is based
on the use of: flexible tines harrow, weeding harrow and roll-star cultivator.
1) One passing with flexible tines harrow on the frozen and well prepared field, at the end of
January-February.
2) Two false sowings with 8 mm teeth weeding harrow (weeds at fully developed cotyledons
stage).
3) One delayed sowing at the end of traditional sowings.
4) One weeding with 6 mm teeth weeding harrow with 2 primary leaves at the unifoliolate
node (weeds at fully developed cotyledons stage).
5) One weeding with 6 mm teeth weeding harrow with 2 leaves soyabean above the
unifoliolate node (weeds at fully developed cotyledons stage).
6) Roll-star cultivator with 2 leaves soyabean above the unifoliate node (weeds from the stage
of fully developed cotyledons to the one with 2 leaves).
This technique did not allow a sufficient weed control either for mono or for dicotyledons.
Echinochloa crus-galli and Fallopia convolvulus caused a decrease in yields during several
trials.
Yields decreased of 6-24 % against conventional agricultural test.
128
Discussion
A single harrowing on hard and common wheat often stimulated the birth of weeds, therefore
the most effective harrowing interventions were the ones made on couple or triplet
The technique of 3 harrowing turned out to be more effective in weed control in all cases and,
in particular, to improve the control of winter grass weeds. In order to control winter grass weeds it
was useful to bring forward the execution of the first intervention in December (3rd leaf) and to
make the following ones in January and February.
Depending on the time of the intervention and on climate, weeds reacted in a different way to
harrowing interventions. During post-emergence treatments, the weeding harrow has turned out to
be more effective on dry fields in windy and sunny afternoons.
The technique developed for weed control in sunflower proved to be particularly easy in late
sowings thanks to the competition of the great leaves of the plants (at harvest the seeds of
Chenopodium a. were green again).
On the other hand the results obtained in weed control in soyabean April/May sowings were
not satisfying, therefore in the present year we are developing some techniques of deep hoeing in
order to improve the control of the perennial weeds (Echinochloa crus-galli and Polygonum
convolvulus) in organic arable crops.
Acknowledgements
The programmes are implemented with the financial support of Regione Emilia-Romagna and
of Provincia di Ravenna
References
D. C. CLOUTIER, R. MARCOTTE, M. L. LEBLANC. Impiego delle colture intercalari e da
sovescio per il controllo delle infestanti. Bio agricultura n° 30: 19-21. 1995.
L. DAL RE, C. DONATI. Colture erbacee questioni di soglia. Supplemento a Il conto terzista n° 5:
7-18. 2000.
L. DAL RE. Criteri e macchine per gli interventi sulle colture erbacee. Supplemento a Terra e Vita
n° 22: 11-17. 2001.
F. DIOMEDE. Il controllo delle erbe infestanti. Bio agricultura n° 69: 32-34. 2001.
U. FRONDONI, P. BARBERI. Attrezzature per le colture erbacee. Supplemento a Il conto terzista
n° 5: 19-25. 2000.
U. FRONDONI. Macchine per il diserbo. Bio agricultura n° 69: 35-38. 2001.
U. FRONDONI. Le lavorazioni conservative del terreno. Supplemento a Terra e Vita n° 22: 5-8.
2001.
A. PERUZZI, P. BARBERI, N. SILVESTRI. Strigliatura del terreno. Terra e Vita n° 43: 55-57.
1995.
E. RASO, L. BASTANZIO, C. VAZZANA. Gestione delle infestanti del frumento tenero con
erpice strigliatore. L’Informatore Agrario n° 31: 27-31. 1997.
129
Physical methods for weed control in potatoes
J.A. Ivany
Crops and Livestock Research Centre, Agriculture and Agri-Food Canada
440 University Avenue, Charlottetown, PEI
Canada, C1A 4N6
Abstract
Increasing demand for potatoes (Solanum tuberosum L.) produced organically, increasing costs
of production, and public interest in knowing how crops are produced has resulted in efforts being
intensified to reduce the amount of herbicides applied in potato production. We evaluated the
potential of using different non-chemical techniques and banded herbicide application to achieve
weed control in potatoes. All experiments were conducted on a Charlottetown fine sandy loam soil
from 1998 to 2000. Four replications of 4-row plots, 6 to 10 m long were planted to Russet
Burbank cultivar in all years. Treatment effects on Elytrigia repens and broadleaved weeds were
assessed using determination of weed biomass from 0.25 x 1.0 m quadrats. Yields were obtained at
maturity by mechanically harvesting the two centre plot rows and grading into marketable and total
tubers. A comparison of a between the row rototiller, over row flamer and full plot width finger
weeder to achieve weed control in potatoes showed that the flamer gave greatest control of E.
repens and broadleaved weeds and generally had highest potato marketable and total yield. There
was no difference between flaming at potato emergence or when potatoes were 10 to 15 cm tall.
Flaming twice (just before potato emergence + 2 weeks later) tended to reduce potato marketable
and total yield. When the herbicides metribuzin (pre), linuron (pre), paraquat (just before potato
emergence) or glyphosate were applied (just before potato emergence) in a 30 cm band, and
followed with a between the row weed removal with a rototiller, weed control and potato yields
were comparable with all treatments. Amount of herbicide applied, however, was reduced by 66 %
using this method (IvanyJ@em.agr.ca).
Introduction
Potatoes (Solanum tuberosum L.) are the fourth largest food crop throughout the world and
each year in Canada 155,000 ha are produced for processing use, table use, and for seed.
Herbicides have been used generally in combination with mechanical cultivation, to provide weed
control in the production of potatoes. In recent years, production of potatoes by organic methods
has increased and ongoing research efforts have been intensified to find ways to obtain weed
control without the use of herbicides. Achieving weed control in small acreage, organic production
is possible with several cultivation operations and / or by the use of propane flaming devices but
results have varied depending on equipment used, time of cultivation, frequency of cultivation,
weed population and weed species.
Belinder et al.(2000) examined weed control in potatoes using banded herbicides and different
types of cultivation equipment. They found that pre-hilling weed densities were greater with
cultivation equipment than with broadcast herbicide or banded herbicide + cultivation but potato
yields were not reduced by this greater weed density. They noted that a combination of banded
herbicide and well timed cultivation gave good weed control and crop yield. VanGressel and
Renner (1990a) planted redroot pigweed or barnyard grass in the potato row after hilling and found
that one weed per metre of row reduced total and marketable yield of ‘Atlantic’ cultivar. Rioux et
130
al. (1979) compared potato yield at different hilling times with herbicides and found that there was
no difference among hilling times in weed control or yield when herbicides were used. In
comparing different hilling times without herbicides, hilling at potato emergence gave best control
and yield. VanGressel and Renner (1990b) found that hilling at potato emergence suppressed
weeds more than hilling when potatoes were 30 cm tall in one year only of the two year study
where Echinochloa crus-galli, Amaranthus retroflexus and Cheropodium album were the
predominant weed species present. Eberlein, et al. (1997), found that cultivation was effective at
low weed densities but at high weed densities control was less effective and yields and net returns
were reduced below that for a standard herbicide treatment. Kilpatrick (1993), found that cultivating
several times was as effective as a herbicide program in giving weed control and potato yields were
comparable.
The use of thermal methods of weed control was discussed by Ascard (1988) with mention of
flaming for potato haulm desiccation and flaming has been recently been included in a review
(Bond and Grundy 2001) but no mention is made of use of flaming for weed control in potato crops.
Flaming using a portable gasoil flamer controlled weeds better, produced higher potato yields and
was the least costly method of weed control in Iran (Shimi, 2000).
The objective of the studies reported in this paper was to evaluate alternative methods of weed
control that could provide effective control and reduce or eliminate the use of herbicides in potato
production under Prince Edward Island conditions. Experiments were conducted comparing
mechanical cultivation, herbicide banding and use of a propane flamer to provide control of weeds.
General
All experiments were conducted on a Charlottetown fine sandy loam soil (Orthic Humo-Ferric
Podzol), pH 5.6 to 6.0 from 1998 to 2000. Four replications, in a randomized complete block
design, of 4-row plots, 6 to 10 m long with a guard row on each side were planted to “Russet
Burbank” cultivar in all years at 38-cm spacing in the row with rows 0.9 m apart. Fertilizer was
banded at planting at a rate of 130, 57 and 109 kg/ha of N, P, and K, respectively. With the
exception of the herbicide and cultivation treatments, cultural practices were the same as those
recommended for commercial production. Details of the operations during the course of the
experiments are given in Table 1.
Table 1. Experiment planting, treatment, data collection, and harvest dates for 1998 and 2000.
Experiment
Planted
Physical methods
1998
May 21
1999
May 18
2000
May 23
Banded herbicide
1998
May 21
1999
May 18
Time of flaming
2000
May 23
Treated
Hilled
Weed biomass
Harvested
-emergence June 15
-2 wks later June 30
-emergence June 17
-emergence June 15
July 14
July 10
October 6
July 15
June 28
October 10
July 12
July 11
October 11
- herbicides May 25
- rotovator June 30
- herbicides May 22
- rotovator May 28
July 14
July 10
October 6
July 15
July 8
October 10
- cotyledon June 12
- 1-2 leaf June 21
- 2-4 leaf June 27
July 10
June 28
October 11
131
Herbicides were applied with a tractor mounted, compressed air sprayer which delivered a
spray volume of 200 L ha-1 and at a pressure of 214 kPa. Physical methods of weed control
included a 4-row propane flamer, a flex tine, 4-row finger weeder (Lely), and a 2-row, multi-head
rotovator. The propane flamer was adjusted to provide a 30 cm wide treatment band over the potato
row in a single pass. The finger weeder was set to operate at a depth of 2 to 3 cm and was operated
once in each direction through the plot. Each head on the rotovator tilled an area 60 cm wide
between the two potato rows and weed control treatments within the potato row are describe within
the individual experiments. All plots were hilled before row closure. Weed counts and dry weight
of individual species was obtained by harvesting all weeds present in three quadrats measuring 25
cm x 100 cm from each plot, drying at 800 C for 48 hrs, and weighing. The quadrats were placed
between the potato rows with the short side parallel to the row direction. At maturity, the two
centre plot rows were harvested using a one-row mechanical harvester and tubers were
mechanically graded to obtain marketable and total yield and tuber specific gravity was determined.
In all experiments, data for weed weight and potato yield were subjected to ANOVA by year and
combined across years using ANOVA techniques (Genstat 5 Committee, 1987), and as there were
significant interactions between years, individual year data was presented.
Physical Methods
An experiment was conducted in 1998 and 1999 to compare efficacy of weed control with a
rotovator, flamer and finger weeder. Treatments were applied at potato emergence or two weeks
after potato emergence when potatoes were 8 to 20 cm tall. Weeds were at the 1 to 4 leaf stage at
potato emergence and were at the 3 to 10 leaf stage when treated two weeks after potato emergence.
An experiment was conducted in 2000 to compare using a single cultivation at potato
emergence, a single cultivation two weeks after potato emergence, or a combination of at potato
emergence and again two weeks after potato emergence for weed control efficacy. Treatments were
applied at potato emergence or two weeks after potato emergence when potatoes were 8 to 15 cm
tall. Weeds were at the 1 to 3 leaf stage when treated at potato emergence and at the 4 to 7 leaf stage
when treated after potato emergence.
Banded Herbicides
In 1998 and 1999 selected herbicides were applied in a 30 cm wide band over the potato row
and the area between the row was cultivated using the rotovator. Rates of application of the
herbicides were: metribuzin, 0.5 kg ai ha-1, linuron, 1.0 kg ai ha-1, paraquat, 0.5 kg ai ha-1, and
glyphosate, 0.5 kg ai ha-1. The herbicides metribuzin and linuron were applied pre-emergence
within 5 days after potato planting. Paraquat and glyphosate were applied just prior to crop
emergence when weeds were at the 1 to 3 leaf stage. The rotovator was used between the rows
when the first flush of weeds was in the 2 to 6 leaf stage.
Time of Flaming
An experiment was conducted in 2000 to determine the effectiveness of flaming for weed
control and effect on potato yield. Flaming was conducted at three stages of development
corresponding to when weeds were in the cotyledon stage, at the 1 to 2, or at the 2 to 4 leaf stage.
Additional treatments included flaming once at cotyledon and again at the 1 to 2 leaf stage or
flaming at the 1 to 2 and again at the 2 to 4 leaf stage. Flaming was done as a 30 cm band centred
over the top of the potato row. These treatments were compared to the standard broadcast herbicide
treatment of metribuzin applied at 0.5 kg ai ha-1.
132
Results
Physical Methods
Predominant weeds in the experiment areas in both 1998 and 1999 were Raphanus
raphanistrum, Chenopodium album and Elytrigia repens with several other species in low numbers.
Weed biomass was different between the two years with 1999 having much greater weed biomass
than in 1998 (Table 2). There was no difference in weed control between time of treatment with
any method used. The rotovator gave excellent control between the rows in both years at weed data
collection but there was no control within the row. Weed biomass was collected between the row
before row closure but a second flush of weeds occurred. The flamer and finger weeder controlled
weeds over the whole plot but one treatment was not sufficient to give long term control. The low
biomass of later emerging weeds in 1998 had no effect on potato marketable and total yield
whereas, the greater weed biomass in 1999 reduced yield in the rotovator treatment applied at
ground crack but not when applied post. Hilling after weed data collection helped control weeds in
all plots but weeds were well established in the potato row of the rotovator plots.
Table 2. Effect of different physical methods of weed control in potatoes on weed biomass and
tuber yield.
Control
method
Time applied
Yield (tha-1)
Total weed
biomass
g m-1 D.M.
1998
1999
Marketable
1998
Total
1999
1998
1999
Rotovator
Emergence
6.7
2.3
33.7
18
37
22.6
Rotovator
2 wks after
emergence
2.1
8.8
29.5
22.7
32.4
29.1
Flamer
Emergence
7.2
120.6
33.6
25.9
36.7
37.6
Flamer
2 wks after
emergence
14.9
115.4
32.8
26.8
36.5
38.6
Finger
weeder
Emergence
17.7
107.5
30.9
25.8
34.4
35.9
Finger
weeder
2 wks after
emergence
29.9
99.9
29.1
25.3
31.8
34.8
4.9
15.3
2.4
1.9
7.6
2.9
SED (15 df)
Predominant weeds in the experiment area in 2000 were R. raphanistrum, C. album and
Spergula arvensis with several other species in low numbers. As in the previous experiment the
rotovator provided weed control between the rows but not in the row. The flamer gave the highest
level of control followed by the finger weeder (Table 3). There was no difference between times of
application either alone or when combined in any method used for weed control. Potato marketable
and total yield was not different between methods of control but within methods of control there
were differences in times of application. Yield was less with the flamer used after crop emergence
suggesting effects on crop growth and recovery as weed control was complete. Yield was less with
133
the finger weeder used 2 wks after potato emergence but not with the combined treatment
suggesting yield loss to competition before control was applied.
Table 3. Effect of time of physical weed control methods on weed biomass and potato tuber yield.
Control method
Time applied
Total weed biomass
g m-1 D.M.
Marketable yield
tha-1
Total yield
tha-1
Rotovator
Emergence
72.6
32.4
36.6
Rotovator
2 wks after emergence
46.8
34.4
37.9
Rotovator
Emergence
emergence
88.7
35.1
37.4
Flamer
Emergence
0.9
37.4
40.7
Flamer
0
34.6
36.9
Flamer
Emergence
emergence
0
34.1
36.5
Finger weeder
Emergence
18.7
35.9
39.2
Finger weeder
24
33
36.6
Finger weeder
Emergence
emergence
8.7
36.5
39.7
SED (24 df)
+
+
+
2
2
2
wks
wks
wks
after
after
after
8.7
0.94
0.95
Banded Herbicides
Predominant weeds species in the experiment were E. repens, S. arvensis and R. raphanistrum
in 1998 and all three plus C. album in 1999. E. repens was the most common species in both years.
E. repens and total weed biomass was reduced more in the herbicide + rotovator treatments than the
metribuzin broadcast treatment in both years (Table 4). All herbicide + rotovator treatments had
comparable levels of E. repens and total biomass in both years. E. repens and total weed biomass
was much higher in 1999 than in 1998. Marketable and total yield were not affected by the
remaining weed biomass in 1998, whereas in 1999 both marketable and total yield were reduced in
the metribuzin broadcast, metribuzin banded + rotovator and linuron banded + rotovator compared
to the paraquat or glyphosate banded + rotovator treatments (Table 5).
Time of Flaming
Predominant weeds in the experiment area were Avena fatua and R. raphanistrum with several
other species in low numbers. The potatoes were just at emergence when the 1 to 2 leaf stage
treatment was applied. The flamer in the potato row with rotovator between the rows reduced weed
biomass of the weeds to the level achieved by broadcast herbicide (Table 6). Later treatment
reduced weed biomass more than early treatment which had in a later flush of weeds emerging.
The weed biomass in this study was too low to have an effect on potato yield. Marketable and total
yield was greatest when flaming was done early. Treatment at the 2 to 4 leaf stage, either as a
single or as two applications, resulted in reduced yield compared to the early treatment and the
broadcast herbicide treatment.
134
Table 4. Effect of herbicide in 30 cm band over row and rotovator between row on weed species
biomass.
Control method
Weed biomass - 1998
g m-1 D.M.
Weed biomass - 1999
g m-1 D.M.
Elytrigia
repens
Total
Elytrigia
repens
Total
0.68
2.44
3.55
14.8
Linuron band + rotovator
1.19
2.36
13.25
24.6
Paraquat band + rotovator
0.48
2.1
1.4
3.6
Glyphosate band + rotovator
0.63
2.34
2.95
10.1
Metribuzin broadcast
9.99
13.99
23.05
27
SED (12 df)
0.75
0.91
4.66
8.1
Metribuzin band + rotovator
Table 5. Effect of banded herbicide with cultivation on potato yield.
Control method
Marketable yield
tha-1
Total yield
tha-1
1998
1999
1998
1999
29
24
33.1
32.7
Linuron band + rotovator
29.8
23.9
33.2
31.2
Paraquat band + rotovator
30.2
27.4
33.9
40.9
Glyphosate band + rotovator
33.1
27
36.8
37.7
Metribuzin broadcast
32.7
20.5
36.1
27.2
3.1
1.3
2.7
2.6
Metribuzin band + rotovator
SED (12 df)
135
Table 6. Effect of time of physical weed control on weed biomass and potato tuber yield.
Control method
Weeds stage at
time applied
Total weed
biomass
g m-1 D.M.
Marketable
yield
tha-1
Total yield
tha-1
Flamer
+ cultivator
Cotyledon
Cotyledon
1.55
39.5
44.2
Flamer
+ cultivator
1-2 leaf
1-2 leaf
0.8
37.5
40.8
Flamer
+cultivator
2-4 leaf
2-4 leaf
0.4
35.2
37.7
Flamer
+ flamer
+ cultivator
Cotyledon
Second flush
cotyledon
Second flush
cotyledon
0.25
35.9
38.3
Flamer +
Flamer +
cultivator
1-2 leaf
Second flush
cotyledon
Second flush
cotyledon
0
35.7
38.4
Metribuzin
broadcast
Pre-emergence
0.7
38.9
42.7
0.53
1.1
1.
SED (15 df)
Discussion
Control of weeds using physical methods was successful in these experiments especially by the
use of flaming in the potato row followed by between the row tillage. Weed biomass was reduced
by the treatments and was more effective when multiple treatments were applied. Degree of
reduction in weed biomass was related to the level of weeds present in the test area and at higher
levels of weeds more weed biomass remained. Potato marketable and total yield was not much
affected at low levels of weed biomass but at high levels of biomass yield was reduced especially in
treatments where weeds were not removed in the potato row. Application of selective herbicides or
use of flaming in a band over the potato row and followed by cultivation gave effective weed
control and crop yields. Flaming late or using multiple flaming operations after potato emergence
caused more injury to the potato foliage and resulted in reduced marketable and total potato yield.
These weed control techniques are generally slower than herbicide application which can cover
many more rows at a time. Recently growers of large acreages of potatoes have moved away from
the standard of cultivating several times and hilling before row closure. Most large acreage growers
now use a single hilling operation at potato emergence which precludes the use of cultivation for
weed control after the crop emerges. It is estimated that growers on PEI use this type of hilling
operation on 65% of the 45,000 ha produced each year. The need for non-chemical methods of
136
weed control is especially acute for those growers who wish to produce potatoes on a large scale
using large equipment but without the use of or with minimal use of herbicides.
Acknowledgements
The assistance of Mr. David Main in the conduct of these experiments is gratefully
acknowledged.
References
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crops and haulm-killing in potatoes. 29th Swedish Weed Control Conference, Uppsala, January
27-28, 1988. Vol. 1 reports, p194-207.
BELINDER RR, KIRKWYLAND JJ, WALLACE RW & COLQUHOUN JB (2000) Weed control
and potato (Solanum tuberosum) yield with banded herbicides and cultivation. Weed
Technology 14, 30-35.
BOND W & GRUNDY AC (2001) Non-chemical weed management in organic farming systems.
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EBERLEIN CV, PATTERSON PE, GUTIERI MJ & STARK JC (1997) Efficacy and economics of
cultivation for weed control in potato (Solanum tuberosum). Weed Technology 11, 257-264.
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York, NY.
KILPATRICK JB (1993) A comparison of cultural and chemical methods for weed control in
potatoes. In Proceedings Brighton Crop Protection Conference - Weeds, Brighton, 449-454.
NELSON DC & THORESON MC (1981) Competition between potatoes (Solanum tuberosum) and
weeds. Weed Science 29, 672-677.
RIOUX R, COMEAU JE & GENEREUX H (1979) Effect of cultural practices and herbicides of
weed population and competition in potatoes. Canadian Journal of Plant Science 59, 367-374.
SHIMI P (2000) Use of flamer as a herbicide replacement in potato fields. Turkish Journal of Field
Crops 5, 41-44.
VANGRESSEL MJ & RENNER KA (1990a) Redroot pigweed (Amaranthus retroflexus) and
barnyardgrass (Echinochloa crus-galli) interference in potatoes (Solanum tuberosum). Weed
Science 38, 338-343.
VANGRESSEL MJ & RENNER KA (1990b) Effect of soil type, hilling time, and weed
interference on potato (Solanum tuberosum) development and yield. Weed Technology 4, 299305.
137
Different combinations of weed management methods in organic carrot
L. Radics, I. Gál, P. Pusztai
Szent István University
Faculty of Horticultural Science
Department of Ecological and Sustainable Production Systems
Budapest, Hungary
Abstract
We are comparing 14 combinations of mechanical and also physical weed management
techniques for organic growing of carrot. Crop of our weed management research is carrot because
of its difficulties in weed management (long growing period, poor weed tolerance) and because
carrot needs to be important product of organic farming.
Untreated weedy and herbicide treated plots are the control ones - cultivator, weed brush, hoe,
hand weeding are used for mechanical control and flame weeder for physical control.
Measurements are covering of weeds and carrot and dry mass of them.
We show now the results of last two years from our long-term experiment.
Results of the year 2000 showed that weed brush is the best in interrows for keeping clean but
in 2001 cultivator combined with hand weeding in rows seems to show the best results.
As this example shows agriculture and weed management depends very much on the weather
of the year, but we try to evolve a method, which can be generally used for organic weed control of
carrot.
Introduction
Because of environmental aspects and because of the increasing demand for vegetables come
from ecological farms, more and more farmers convert their conventional farming systems into
ecological farming, not at last because they want to disregard herbicides from production.
(VEREIJKEN & KROPFF, 1996)
Most of the problems caused by weeds occur in the plant of vegetable crop rotation, which has
weak competition ability. Plants, like carrot with slow initial development are very sensitive for
weediness (TURNER, 2000). If the main tool of weed management is still herbicide, these weedsensitive plants increase the amount of utilised herbicide of vegetable production in general.
We have chosen carrot as crop plant because of its wide spacing and its slow initial
development, so it has high weed management risk (BILALIS D et al. 2001). Carrot is important
basic material for healthy food so we need large amount of it from ecological production.
One of the most important questions of environmentally sound plant production is weed
management (TU M et al. 2000). The other important thing is to examine not only the
successfulness of weed management but also the yield of the crops, because our aim is – for
keeping biodiversity (KRISTIANSEN P et al. 2001) - only to decrease weediness under the level of
damage to production and yield and not to destroy them.
Moreover with spreading of environmentally sound farming, development of its production
technology become more and more important (VEREIJKEN & KROPFF, 1996).
Farmers growing crops organically often expect to achieve good control by using only one
mechanical weeder type. It is important therefore that the correct machine is selected. (PULLEN,
1999)
138
This is a field experiment with 15 treatments and 4 repetitions.
Soil cultivation was making fine seedbed for carrot.
Herbicide utilisation was preemergent with mixture of DUAL 960 EC (20mL 100 m-2) and
Maloran 50 WP (20 g 100 m-2)
Used carrot variety was Nanti with 75 cm row distance. Sowing depth was 3 cm.
Times of sowing were 12. 07. 2000. (second sowing) and 04. 04. 2001.
Ecological circumstances
Soil type is restrainedly deep chernozem-like sandy soil. Soil forming rock is calcareous sand.
Depth of humic layer is 30-40 cm. Soil is fast warmer, with good water permeability and good air
capacity. The disadvantage of this soil type, it is inclined to quick cooling down and drying out.
Weakly calciferous, faintly alkaline soil.
Climate: Precipitation of growing season in 2000 were significantly lower (223 mm) than in the
average 1999 year (480 mm) in the same period. During this period the average monthly
temperature was higher with about 10% and because of this dual effects a significant depression
were detected in case of lack of irrigation.
After continuous drought of the year 2000, precipitation of 2001 was enough for emerging and
growing of carrot but also increased weediness.
We did not use any irrigation.
Treatments
In rows:
- weedy control,
- hand weeding,
- herbicide,
- weed flaming
In interrows:
- weedy control,
- hoeing, herbicide,
- weed flaming,
- cultivator,
- weed brush
Combinations of treatments:
1. Control
2. Herbicide on the whole surface
3. Herbicide in the rows + cultivator in the interrows 1x
4. Herbicide in the rows + weed brush in the interrows 1x
5. Herbicide in the rows + hoeing in the interrows 1x
6. Weeding in the rows 1x + cultivator in the interrows 1x
7. Weeding in the rows 1x + cultivator in the interrows 2x
8. Weed flaming on whole surface + cultivator in the interrows 1x
9. Weed flaming on whole surface + cultivator in the interrows 2x
10. Weeding in the rows 1x + weed brush in the interrows 1x
11. Weeding in the rows 1x + weed brush in the interrows 2x
12. Weed flaming on whole surface + weed brush in the interrows 1x
13. Weed flaming on whole surface + weed brush in the interrows 2x
14. Weeding in the rows according to need + weed brush in the interrows 2x
15. Weeding in the rows according to need + cultivator in the interrows 2x
139
Sampling
- weed surveys: right before and two weeks
after treatments
- dry mass of weeds, of root and leaf of
carrot right before and two weeks after
treatments, both in the rows and interrows
in the case of weeds (weeds have taken for
measuring from 0,25 m2 in the rows and
from 0,5 m2 in interrows)
Research schedule:
In 2001:
In 2000:
19. 07. - sampling
19. 04. - sampling
21. 07. - weed flaming in 8. 9. 12. 13. treatments
19. 04. - weed flaming in 8. 9. 12. 13. treatments
herbicide in 2., 3., 4. 5. treatments
herbicide in 2., 3., 4. 5. treatments
02. 08. - sampling
02. 05. - sampling
03. 08. - cultivator in 3., 6., 7., 8., 9., 15. treatments
09. 05. - sampling
weed brush in 4., 10., 11., 12., 13., 14. treatments 14. 05. - cultivator in 3., 6., 7., 8., 9., 15. treatments
16. 08. - sampling
weed brush in 4., 10., 11., 12., 13., 14. treatments
28. 08. - cultivator in 7., 9., 15. treatments
hand weeding in 6., 7., 10., 11., 14., 15. treatments
weed brush in 11., 13., 14. treatments
30. 05. - sampling
hand weeding in 6., 7., 10., 11., 14., 15. treatments15. 06. - sampling
hoeing in 5. treatment
25. 06. - cultivator in 7., 9., 15. treatments
12. 09. - sampling
weed brush in 11., 13., 14. treatments
29. 09. - hand weeding in 14., 15. treatments
hoeing in 5. treatment
13. 10. - sampling
09. 07. - sampling
09. 08. - sampling
10. 08. - hand weeding in 14., 15. treatments
23. 08. - sampling
19. 09. - sampling
We used SPSS 9.0 program for analysing data and Tukey’s test for comparing means.
Results
In the year 2000 we did not find any significant differences between the weed cover of
treatments at the first survey so we found that experiment area was homogenous in view of
weediness.
We can make homogenous groups from dry mass of weeds in rows in herbicide treatments
(treatments 2., 3., 4., 5.). Two weeks after the first treatments herbicide treatments made statistically
homogenous group and caused significantly lower mass of weeds than flamed ones (Fig. 1.).
140
Legend:
1. Control
2. Herbicide
3. Herbicide in rows + cultivator in interrows 1x
4. Herbicide in rows + weed brush in interrows 1x
5. Herbicide in rows + hoeing in interrows 1x
6. Weeding in rows 1x + cultivator in interrows 1x
7. Weeding in rows 1x + cultivator in interrows 2x
8. Weed flaming + cultivator in interrows 1x
9. Weed flaming + cultivator in interrows 2x
10.
11.
12.
13.
14.
Weeding in rows 1x weed brush in interrows 1x
Weeding in rows 1x + weed brush in interrows 2x
Weed flaming + weed brush in interrows 1x
Weeding in rows according to need + weed brush in interrows
2x
15. Weeding in rows according to need + cultivator in interrows
2x
Figure 1. Dry mass of weeds in rows. Sample from 02. 08. 2000.
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
Herbicide in rows + cultivator in interrows 1x
Herbicide in rows + weed brush in interrows 1x
Herbicide in rows + hoeing in interrows 1x
Weeding in rows 1x + cultivator in interrows 1x
Weed flaming + cultivator in interrows 1x
9.
10.
11.
12.
13.
14.
15.
Weeding in rows according to need + weed brush in interrows 2x
Weeding in rows according to need + cultivator in interrows 2x
Figure 2. Dry mass of weeds in interrows. Sample from 16. 08. 2000.
141
In interrows (Fig. 2.) weed brush treatments (treatments 4., 10., 11., 12., 13., 14.) made
significantly lower dry mass of weeds and they made statistically homogenous group. Utilisation of
cultivator in interrows (treatments 3., 6., 7., 8., 9., 15.) seemed to be less effective with its two
outstanding values (treatments 6., 8.). Herbicide, utilised on the whole surface (treatment 2.) is still
effective one month after its passing out.
At the end of the growing season every treatments decreased the dry mass of weeds in the rows
compared to untreated control (Fig. 3.). Weeding in the rows according to need was the most
effective from all treatments and these ones (treatments 14., 15.) made a homogenous group too.
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
9.
10.
11.
12.
13.
14.
15.
Figure 3. Dry mass of weeds in rows. Sample from 13. 10. 2000.
At the end of the growing season herbicide, utilised on the whole surface (treatment 2.) lost all
of its effect and we found higher mass of weeds in these interrows than in the interrows of untreated
control (Fig. 4.).
Utilisation of weed brush gave better results for the end of the growing season than cultivator
treatments except treatment 15.
Cultivator (treatments 7., 9., 15.) and also weed brush used twice (treatments 11., 13., 14.)
showed better results in all cases than if we used them once (cultivator: treatments 3., 6., 8.) (weed
brush: treatments 4., 10., 12.).
Higher mass of weeds were observable in all cases when utilisation of cultivator or weed brush
was combined with weed flaming in interrows. Relying upon these findings utilisation of weed
flaming is not seemed to be economic. Beside this we can find that weed flaming combined with
two mechanical interrow treatments like cultivator and weed brush (treatments 9, 13) was more
effective than we used them only on one occasion (treatments 8, 12).
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
142
9.
10.
11.
12.
13.
14.
15.
Figure 4. Dry mass of weeds in interrows. Sample from 13. 10. 2000.
It can give interesting results to examine weeds, which are arranged in groups by life forms:
T = therophyte
T1 – plants, which are spearing in fall and ripening
in spring
T2 – plants, which are spearing in fall and ripening
in the beginning of summer
T3 – plants, which are spearing in spring and
ripening in the beginning of summer
T4 – plants, which are spearing in spring and
ripening in the end of summer
G = geophyte (plants, which are overwintering on the soil
surface or under soil and has slanting or horizontal
underground stem)
G1 - plants, which have stole near to the soil surface
G3 - plants, which have stole in deeper and many levels of
the soil
Results of weed survey arranged to groups by life forms show that weeds of the examination
are mainly members of the T life form group.
Herbicide treatment applied on the whole surface reduced the cover of weeds of T-life from.
On the other hand this treatment had no effect on the weeds of G-life form and what is more,
herbicide made better life circumstances for these weeds with driving back of T-life formed weeds
and promoted their spread.
Under the influence of mechanical weed control occurred twice in interrows, cover of geophyte
weeds increased, which is explainable with cutting up stoles and rhizomes. The same treatment had
the opposite effect on T-life formed weeds: efficiently reduced their cover in all cases.
On perennial weeds there was no significant effect of any row treatments.
With one-time hand weeding of rows we found no significantly better result not in any life
form groups, than in the case of any other treatments in the rows. Even repeated hand weeding
caused significantly lower weed cover but only in the case of T4-life form group.
143
In the year 2001 at the beginning of the growing season every treatments decreased the dry
mass of weeds in the rows compared to untreated control.
If we examine the question of weed cover with life form groups than also weed flaming and
herbicide utilisation caused significant reduction only on the weed species of T4-life form group in
rows and interrows alike.
Cultivator-treated interrows make statistically homogeneous group (Fig. 5.) and are different
from weed brush-treated ones, in which cover of T4-weeds were much higher two weeks after the
treatment.
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
9.
10.
11.
12.
13.
14.
15.
Figure 5. Cover of weeds in T4 life form group in interrows. Sample from 30. 05. 2001.
These differences are observable one month after the treatment, so cultivator can be called
effective for a relative long term in interrows against annual weeds, which germinate from seed.
After the next interrow treatments hoeing and cultivator caused the lowest dry mass of weeds.
Hoeing decreased better the mass of weeds, maybe because of greater preciseness of this method,
but we have to take notice of the lack of manpower and its costs.
At the end of the growing season significantly lower weed cover was observable in rows in the
following treatments: herbicide on the whole surface (treatment 2.), herbicide in the rows and
hoeing in the interrows 1x (treatment 5.), weeding in the rows according to need and weed brush in
the interrows 2x (treatment 14.), weeding in the rows according to need and cultivator in the
interrows 2x (treatment 15.).
Among the above mentioned treatments the last one (treatment 15.) showed the best results in
weed cover and in dry mass of weeds too (Fig. 6.).
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
144
9.
10.
11.
12.
13.
14.
15.
Figure 6. Total cover of weeds in rows. Sample from 19. 09. 2001.
Weed covers in interrows are similar (Fig. 7.) except treatment 5. with hoed interrows, which
showed worse results. On the other hand there is bigger difference between treatment 14. and 15.,
so we can see that in this year cultivator was much more effective than weed brush and it had better
effect also on the crop.
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
9.
10.
11.
12.
13.
14.
15.
Figure 7. Total cover of weeds in interrows. Sample from 19. 09. 2001.
145
In ineffectiveness of weed brush had big role the dry weather at the time of occurrence, which
reduced effectiveness of weed brush with higher rate than in the case of cultivator. Because of dry
soil surface weed brush only rubbed off the leaves of weeds and was not able to penetrate into the
topsoil where it could better destroy annual weeds, which germinate from seed.
This difference was observable until the end of growing season but at that time with much
lower rate.
1.
2.
3.
4.
5.
6.
7.
8.
Legend:
Control
Herbicide
9.
10.
11.
12.
13.
14.
15.
Figure 8. Dry mass of carrot roots. Sample from 19. 09. 2001.
Cultivator, and hoeing had better effect on the growing of carrot than weed brush had (Fig. 8.)
so moving the soil in interrows serves not just for weed control but it is good also for the crop plant.
Apart from the fact that weeds in interrows meant concurrence for carrot, moving of soil in a larger
extent can also help growing of carrot – surely cultivator and hoeing cause larger soil moving than
weed brush.
It is noticeable that we reached the lowest weed cover and dry weed mass and the highest yield
of carrot in treatment with cultivator occurred twice in interrows and weeding in rows according to
need (treatment 15.). The second best treatment was herbicide utilised on whole surface but the
difference from the other treatments was not significant in this case.
Discussion
In 2000. under extremely dry and warm circumstances we took the following conclusions:
- herbicide treatment was the most effective treatment
- weed brush was more effective in weed management than cultivator
- both equipment gave satisfactory results if we occurred them twice
- mechanical weed control reduced cover of therophyte weeds but increase the cover of
geophyte weeds
146
In 2001. under less dry circumstances:
- the most effective treatment was weeding in rows according to need and cultivator in
interrows occurred twice
- because the above mentioned treatment combination was more effective, than herbicide
utilisation and it had higher yield increasing effect too, we can say that herbicide utilisation
can be taken out from ecological carrot production
- cultivator occurred twice and many times row weeding cause higher expenses which is
common in ecological farming. But in the same time it give higher yield and also product of
higher value
- weed brush showed very bad effectiveness even if we occurred it twice. To choose the time
of its utilisation needs more attention than in the case of cultivator (PULLEN D. 1999)
- higher carrot cover was in the treatment with lower weed cover
Acknowledgements
OTKA T 030346 supported experiment.
References
BILALIS D, EFTHIMIADIS P, SIDIRAS N (2001) Effect of three tillage systems on weed flora in
a 3-year rotation with four crops, Journal of Agronomy and Crop Science 186 (2), 135-141.
KRISTIANSEN P, SINDEL B, JESSOP R (2001) The importance of diversity in organic weed
management
PULLEN D (1999) Field work, A look at the performance of different field weeders, Organic
farming 61, 18-19.
TU M, HURD C, RANDALL JM (2001) Weed Control Methods Handbook, The Nature
Conservancy
TURNER B (2000) The heat is on – thermal weed control, Organic farming 65, 17-18.
VEREIJKEN P & KROPFF MJ (1996) Prototyping ecological farming systems. In: Annual Report
of the DLO Research Institute for Agrobiology and Soil Fertility, Wageningen, the Netherlands
147
Options for mechanical weed control in grain maize
– effects on weeds
D.A.G.A.E., Settore Meccanica Agraria, Università di Pisa, Italy; 2Scuola Superiore Sant’Anna,
Pisa, Italy; 3Centro Interdipartimentale di Ricerche Agro-ambientali E. Avanzi, S. Piero a Grado,
Pisa, Italy
1
Abstract
Two field experiments were carried out in 2000 and 2001 on a loamy soil to test different
options for mechanical weed control (harrowing or hoeing) in grain maize (Zea mays L.) sown in 50
cm-spaced rows. The first experiment tested different four tine adjustments of a 3 m-wide springtine harrow equipped with 6 mm-diameter tines. The second experiment compared four different
hoeing techniques: (1) a PTO-powered rotary hoe, (2) a precision hoe with sweep and goose-foot
shares, (3) a precision hoe (as before) + torsion weeder, (4) a precision hoe (as before) + torsion
weeder with tines crossed. Each treatment was replicated three times. Both experiments also
included a weedy check. In both experiments, weed density was sampled by species just before and
two weeks after the treatment in one fixed quadrat (100 x 50 cm) per plot, used later also for the
determination of weed biomass at maize harvest. Results of both experiments indicated that: (1)
short-term weed density reduction, although often considerable in absolute values, did not seem
related neither to weed biomass at harvest nor to maize yield; (2) maize yield was higher with
hoeing than with harrowing but was likely influenced by factors other than weed control; (3) there
is no clear advantage in using one adjustment of the spring-tine harrow or one hoeing implement
over the others and, for this reason, further research is needed.
Introduction
Grain maize (Zea mays L.) is one of the major arable crops in Italy. Conventional maize
production is often based on continuous cropping of the cereal, high input of nitrogen fertilisers and
use of residual herbicides (e.g. triazines) that altogether pose a serious environmental threat. As
such, sustainable maize production, amongst other things, relies on the development of effective
alternatives to broadcast herbicide application. Integrated maize systems can include low-rate or
banded herbicide spraying coupled with mechanical weeding (Pleasant et al., 1994; Buhler et al.,
1995; Leblanc et al., 1995) and/or the use of cover crops to suppress weeds (Teasdale et al., 1991;
Burgos & Talbert, 1996; Bàrberi & Mazzoncini, 2001). The optimisation of mechanical weed
control is obviously particularly important in organic maize production, where to date mechanical
implements represent the most widespread and economically viable option for direct weed control.
The aim of this study was to compare the effects on weeds of different harrowing and hoeing
treatments used for direct weed control in grain maize. Results on work parameters of the different
technical options and on crop yield are reported elsewhere (Raffaelli et al., 2002).
Materials & Methods
In 2000 and 2001, two field experiments were carried out on a loamy soil at the Centro
Interdipartimentale di Ricerche Agro-ambientali E. Avanzi of the University of Pisa (43°40' lat. N,
148
10°19' long. E) to evaluate different options (harrowing or hoeing) for mechanical weed control in
grain maize. In both experiments, the soil, that in the previous year hosted a winter wheat (Triticum
aestivum L.) crop, was mouldboard-ploughed at ca. 30 cm depth in winter. The false seedbed
technique was used in 2001 only. The crop received pre-sowing mineral fertilisation with 80 kg ha-1
N, 120 kg ha-1 P2O5 and 120 kg ha-1 K2O. Further 160 kg ha-1 N were top-dressed at the 4th leaf
stage. Maize cv. PR34B23 (FAO class 500) was sown on 6 May 2000 and 2 May 2001 in 50 cmspaced rows at a seeding rate of 8.1 seeds m-2.
Harrowing experiment
The harrowing experiment compared four tine adjustments of a 3 m-wide Malin spring-tine
harrow equipped with 6 mm-diameter tines. Tine adjustments were: –30°, -15°, 0° and +15°, where
values represent the angle E between the upper part of the tine and the perpendicular to the soil
surface (Fig. 1). The harrow was passed only once, on 19 June 2000 and 31 May 2001, when maize
was at the 4th and 3rd leaf stages respectively.
+ JE
D
)
Hoeing experiment
The hoeing experiment compared four weed control implements: (1) a PTO-powered rotary
hoe, (2) a precision hoe with sweep and goose-foot shares, (3) a precision hoe (as before) + torsion
weeder (PH + TW), (4) a precision hoe (as before) + torsion weeder operated with the tines crossed
(PW + TWC). Hoeing was performed only once, on the same dates of the harrowing treatments and
at the same crop growth stages.
In both experiments, a weedy check was included and treatments were allocated in a
randomised complete block design with three replicates. Size of the elementary plots was 25 m
length by 3 m width in both experiments.
Data collection and analysis
In both experiments, plant density (crop and weeds) was sampled by species just before weed
control treatments (on 19 June 2000 and 29 May 2001) and ca. two weeks after the treatments (on 3
July 2000 and 15 June 2001) in one fixed quadrat (100 x 50 cm) per plot, divided into an outer and
inner part to account separately for between-row and within-row weed control. The same quadrats
were used for sampling weed biomass at maize harvest (on 13 October 2000 and 26 September
2001). The collected biomass was divided by species and placed in an oven at 80°C until constant
weight. Data shown in this paper refer to the whole quadrat size.
149
Plant density and biomass of the total weed community and of major species were subjected to
statistical analysis. Crop and weed densities after mechanical weed control were expressed as
percent reduction relative to initial plant density. Prior to ANOVA, data were arcsine-, square rootor log- transformed, as appropriate (Gomez & Gomez, 1984). Treatment means were separated by a
LSD test at P d 0.05. Data shown in tables are back-transformed means.
Results
Total weed density just before weed control treatments was much higher in 2000 (99.8 plants
-2
m ) than in 2001 (12.4 plants m-2), a likely consequence of the application of the false seedbed
technique in the second year. In both years, the weed community was dominated by Amaranthus
retroflexus (69.8% and 40.9% of total density in 2000 and 2001 respectively), while initial presence
of Solanum nigrum in 2000 (20.8%) and of Convolvulus arvensis in 2001 (12.9%) was also
noteworthy.
Maize was not uprooted at all by harrowing in 2000, while in 2001 percent maize plant
reduction was negligible (< 4%) and not influenced by tine adjustment.
In 2000, use of the more aggressive tine adjustment (+15°) increased total percent weed
reduction as compared to the least aggressive one (-30°). In 2001, weed reduction was lower than in
the previous year for any tine adjustments, ranging from 30.1 to 69.9% (Table 1). In the first year,
A. retroflexus control was higher with +15° and 0° than with -15° and -30°, while control of S.
nigrum did not change substantially among tine adjustments (Table 1).
Table 1. Harrowing experiment. Percent reduction in weed density observed in maize 14 DATa in
2000 and 17 DAT in 2001.
Total weeds
Amaranthus
Solanum
Tine adjustment
retroflexusb
nigrumb
2000
2000
2000
2001
+15°
91.5 a
97.8 a
91.7 a
69.9 a
0°
93.2 a
95.8 a
83.3 ab
30.1 b
-15°
78.4 b
96.5 a
74.8 ab
56.4 ab
-30°
66.8 b
82.2 a
63.4 b
62.8 ab
Weedy check
4.8 c
7.3 b
17.1 c
0.9 c
a
b
Days After Treatment. In 2001 density of these species was too low to perform a reliable
statistical analysis. In each column, means followed by the same letter are not significantly different
at P d 0.05 (LSD test). Data shown are back-transformed means (following arcsine-transformation).
Total weed biomass at harvest differed significantly among treatments only in 2001, when it
was higher in -15° (value not significantly different from that of the weedy check) and lower in 0°
(Table 2). The former treatment also had a higher biomass of A. retroflexus in 2000 and of C. album
in 2001. Compared to the weedy check, biomass of C. arvensis in 2001 was significantly lower only
in +15° (Table 2).
Hoeing experiment
Like in the harrowing experiment, total initial weed density was much higher in 2000 than in
2001 (56.0 vs. 7.9 plants m-2). Initially, the weed community was dominated by Amaranthus
150
retroflexus (78.1% and 32.2% of total density in 2000 and 2001 respectively) and, to a lower extent,
by Solanum nigrum in 2000 (20%), and Chenopodium album (10.2%), Convolvulus arvensis
(11.9%) and Datura stramonium (10.2%) in 2001.
Table 2. Harrowing experiment. Dry biomass (g m-2) of the major weed species and of total weeds
observed at maize harvest in 2000 and 2001.
Total weeds
Amaranthus Chenopodium Convolvulus
a
a
a
Tine adjustment Retroflexus
album
arvensis
2000
2001
2001
2000
2001
+15°
5.7 ab
3.3 ab
0.0 b
6.1 ns
15.6 bc
0°
2.4 b
0.0 b
2.6 ab
7.7 ns
2.6 c
-15°
18.0 a
11.3 a
0.9 ab
18.1 ns
59.3 ab
-30°
1.7 b
0.0 b
2.8 ab
7.2 ns
14.2 bc
Weedy check
3.9 ab
19.7 a
12.5 a
5.4 ns
104.7 a
a
In the year not shown in table, density of these species was too low to perform a reliable statistical
analysis. In each column, means followed by the same letter are not significantly different at P d
0.05 (LSD test), ns = not significant. Data shown are back-transformed means (following logtransformation).
Hoeing treatments did not harm the crop (density reduction was 0% in 2000 and 2% in 2001).
Percent reduction in weed density (Table 3) did not significantly differ among the hoeing treatments
but, averaged over all the hoeing options, was higher in 2000 (76.9%) than in 2001 (48.3%). The
same effect was observed on S. nigrum in 2000, while A. retroflexus density was reduced to a
greater extent by the rotary hoe than by the precision hoe (Table 3).
Table 3. Hoeing experiment. Percent reduction in weed density observed in maize 14 DATa in 2000
and 17 DAT in 2001.
Total weeds
Amaranthus
Solanum
b
b
Treatment
retroflexus
nigrum
2000
2000
2000
2001
Rotary hoe
94.9 a
75.0 a
96.0 a
32.9 a
Precision hoe
48.3 b
75.0 a
50.4 ab
25.0 a
PH + TW
73.1 ab
97.2 a
75.9 ab
79.7 a
PH + TWC
85.4 ab
94.9 a
85.1 a
55.7 a
Weedy check
4.8 c
7.3 b
17.1 b
0.9 b
a
Days After Treatment. bIn 2001 density of these species was too low to perform a reliable
statistical analysis. PH + TW = precision hoe + torsion weeder, PH + TWC = precision hoe +
torsion weeder with tines crossed. In each column, means followed by the same letter are not
significantly different at P d 0.05 (LSD test). Data shown are back-transformed means (following
arcsine-transformation).
In 2000, total weed biomass at harvest was generally low but higher in PH + TW and the
weedy check than in any other treatments, due to a higher biomass of A. retroflexus, the major weed
(Table 4). In 2001, final biomass in the hoeing treatments was ca. one tenth of that measured in the
weedy check, and lowest in PH + TWC. However, no significant differences among treatments
were observed in the final biomass of the three species more abundant at maize harvest (C. album,
C. arvensis and S. nigrum).
151
Discussion
In the harrowing treatments, despite the usually high reduction in weed density observed 2 to 4
weeks after the pass and a much lower total weed biomass at harvest in 2001, grain yield was not
significantly different to that of the weedy check (data not shown). This effect can only partly be
explained by high between-plots variation. Summer drought (the crop was rainfed) may have
levelled differences in maize grain yield (which ranged from 5.8 to 8.2 t ha-1) and thus masked
treatment effects. Lack of significant correlation between short-term weed control by harrowing and
crop and weed biomass at harvest confirms what has been previously observed in the same
environment on durum wheat (Bàrberi et al., 2000).
Table 4. Hoeing experiment. Dry biomass (g m-2) of the major weed species and of total weeds
observed at string bean final harvest in 2000 and 2001.
Total weeds
Amaranthus Chenopodium Convolvulus Solanum
a
a
a
a
album
arvensis
nigrum
retroflexus
Treatment
2000
2001
2001
2001
2000
2001
Rotary hoe
0.7 c
1.6 ns
2.0 ns
0.6 ns
0.7 b
11.3 b
Precision hoe
0.6 c
1.0 ns
6.1 ns
0.4 ns
0.9 b
17.9 ab
PH + TW
2.0 ab
2.0 ns
3.8 ns
0.2 ns
3.3 a
10.1 b
PH + TWC
1.0 bc
0.3 ns
0.5 ns
1.7 ns
1.0 b
4.4 b
Weedy check
3.9 a
19.7 ns
12.5 ns
1.1 ns
5.4 a
104.7 a
a
In the year not shown in table, density of these species was too low to perform a reliable statistical
analysis. PH + TW = precision hoe + torsion weeder, PH + TWC = precision hoe + torsion weeder
with tines crossed. In each column, means followed by the same letter are not significantly different
at P d 0.05 (LSD test), ns = not significant. Data shown are back-transformed means (following
log-transformation).
Compared to the harrowing experiment, in the hoeing one maize yields were higher (up to 9.5 t
ha-1) and use of precision hoeing, PH + TW and PH + TWC resulted in higher yield than use of the
rotary hoe, although only in 2000. Again, this effect cannot be explained by weed density and
biomass data. It can be hypothesised that rotary hoeing might have damaged maize roots to a
greater extent than the other treatments, especially when considering that in 2000 mechanical
weeding was performed 21 days later than in 2000, i.e. in a period when maize root growth and
functioning was likely higher. Total weed biomass at harvest was unrelated to total initial weed
density.
Data of this paper would suggest that hoeing may be preferable to harrowing for direct weed
control in maize, but a global evaluation of the different options must also take into account work
parameters as well as energy (and consequently economic) issues: these issues, that are discussed in
Raffaelli et al. (2002), may change the relative advantage of treatments from year to year, e.g.
depending on soil workability.
152
Acknowledgements
The authors wish to thank all the staff of the Centro Interdipartimentale di Ricerche Agroambientali E. Avanzi, University of Pisa for their precious help in the conduction of the
experiments and sample collection and processing.
References
BÀRBERI P & MAZZONCINI M (2001) Changes in weed community composition as influenced
by cover crop and management system in continuous corn. Weed Science 49, 491-499.
BÀRBERI P, SILVESTRI N, PERUZZI A & RAFFAELLI M (2000) Finger harrowing of durum
BUHLER DD, DOLL JD, PROOST RT & VISOCKY MR (1995) Integrating mechanical weeding
with reduced herbicide use in conservation tillage corn production systems. Agronomy Journal
87, 507-512.
BURGOS NR & TALBERT RE (1996) Weed control and sweet corn (Zea mays var. rugosa)
response in a no-till system with cover crops. Weed Science 44, 355-361.
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for agricultural research, 2nd edn, 467-471, J. Wiley & Sons, New York, USA.
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dans le maïs-grain par une application d'herbicides en bandes combinée à des sarclages
mécaniques. Weed Research 35, 511-522.
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management in corn (Zea mays). Weed Technology 8, 217-223.
control in maize – work parameters and crop yield. In: Proceedings 5th Workshop of the EWRS
Working Group on Physical and Cultural Weed Control, Pisa, Italy, 11-13 March.
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residue. Weed Science 39, 195-199.
153
Options for mechanical weed control in grain maize
- work parameters and crop yield
1
M. Raffaelli1, A. Peruzzi1, P. Bàrberi2 & M. Ginanni3
D.A.G.A.E., Settore Meccanica Agraria, University of Pisa, Italy; 2Scuola Superiore Sant’Anna,
Pisa, Italy; 3Centro Interdipartimentale di Ricerche Agro-ambientali “E. Avanzi”,
S. Piero a Grado, Pisa, Italy
Introduction
Machines for physical weed control having completely different mechanical and operative
characteristics are often used on the same crop and/or soil; this is not always logic and explicable,
since it is like if a tractor, a city car or a Ferrari were used indifferently for driving. This behaviour
is a consequence of lack of knowledge that is not simple to tackle, given the complexity of
phenomena related to weed management that need to be taken into account (Bàrberi, 2002).
Experiments are then required to allow in-depth analysis of the interactions between machine
working tools and soil conditions, crop typology and management practices, as well as weed
typology, density, developmental stage and competitiveness (Kouwenhoven & Terpstra, 1979;
Bàrberi et al., 2000; Cloutier & Leblanc, 2000; Leblanc & Cloutier, 2000a and 2000b; Kurstjens &
Bleeker, 2000; Kurstjens et al., 2000; Kurstjens & Kropff, 2001; Raffaelli et al., 2000).
The present study (that is part of a more complex study) aimed to investigate the performances
of different machines for weed control having very different characteristics when operated on the
same soil and the same crop.
Trials were carried out on adjacent fields using a spring-tine harrow in one experiment, and a
precision hoe equipped or not with torsion weeders and a PTO-powered rotary hoe in another
experiment. All the implements are 3 m-wide.
The spring-tine harrow (Malin) is composed of two small modular frames each 1.5 m-wide.
Each small frame is composed of 6 transverse rows of 8 tines; each tine is 36 cm long and has a 0.6
cm diameter. Tines, made of special-purpose steel, are J-shaped and composed of a 25 cm long
vertical segment followed by a second shorter segment (11 cm) angled at 135˚ to the first segment
in the working direction of the machine.
The precision hoe (with manual steerage) has sweep and goose-foot shares and can be equipped
with torsion weeders.
The PTO-powered rotary hoe is a conventional machine with L-shaped tools.
A 30 kW 2WD tractor was always used to perform the experimental treatments.
Trials were conducted in 2000 and 2001 at the Centro Interdipartimentale di Ricerche Agroambientali “E. Avanzi” of the University of Pisa (43°40’ Long. N, 10°19’ Lat. E). Soil physical and
mechanical characteristics are shown in Table 1. Details on the experimental layout are reported by
Raffaelli et al. (2002a).
154
Maize (Zea mais L. cv. PR34B23, FAO Class 500) was grown according to the standard
agricultural practices in the study area (Raffaelli et al., 2002a) and sown at a density of 8.1 plants
m-2 and an inter-row spacing of 50 cm.
Immediately prior to mechanical weeding, soil water content (percentage compared to fresh
mass), dry bulk density and cone resistance were determined. The soil consistency index at the time
of harrowing was calculated on the basis of Atterberg limits and soil water content measurements.
from –30° up to +15°, where values represent the angle E between the upper part of the tine and the
perpendicular to the soil surface, see Fig. 1).
The hoeing experiment compared four different hoeing systems: a PTO-powered rotary hoe, a
precision hoe with sweep and goose-foot shares, a precision hoe (as before) + torsion weeders, and
a precision hoe (as before) + torsion weeders operated with the tines crossed.
Several harrowing or hoeing work parameters were measured and calculated for any
treatments: these included working depth, speed and capacity; fuel consumption per hectare and
hour, drawbar pull, useful power, direct input and tractor skidding.
Maize yield was determined by complete harvest of 2 m of crop row selected in the central part
of each plot.
Table 1. Soil physical and mechanical characteristics.
Characteristics
Values
2000
Texture (%)
Sand
(%)
Silt
(%)
Clay
(%)
Classification
Liquid limit (LL, %)
Plastic limit (PL, %)
Plasticity index (LL-PL)
Soil water content (%)
Consistency index
Dry bulk density
Cone resistance (0-5 cm)
Ø > 2 mm
0.02 < Ø d 2 mm
0.002 < Ø d 0.02 mm
Ø d 0.002 mm
ISSS System
-3
Kg dm
MPa
2001
0
58
32
10
sandy-loamy
24
15
9
11
1.4
1.3
0.2
11
1.4
1.4
0.7
155
+ JE
D
)
All the experiments were carried out on the same soil type. Analysis of the data shown in Table
1 shows that at time of harrowing the soil was in good condition for being tilled; on the second
year, cone resistance, although showing not very high absolute values, was 3.5 times higher with
than in the first year. The soil consistency index did not differ between years. It can be hypothesised
that, despite the soil had the same total water content in both years, water uptake and distribution
processes differed as to make the soil harder in the second year.
Mechanical and operative characteristics of harrowing and hoeing operations are shown in
Tables 2 and 3.
The working depth of the harrow increased with tine angle in the first year, but values were
generally low and the increase in depth was not as pronounced as in previous experiments (Bàrberi
et al., 2000). In the second year, the working depth was even lower, showing values that cannot
easily be explained by soil characteristics. Tines had difficulty to penetrate the soil especially in the
second year, when mean working depth was 1.2 cm and tine adjustment had a very little influence
on soil penetrability. In contrast, the working depth of hoes did not vary between years and, as
expected, was higher than that of the spring-tine harrow. It should be stressed that, with the
machines used, it is hardly possible to hoe at a lower depth than that observed in these experiments.
Working speed and productivity of all machines showed only very slight differences between
the two years. Absolute values recorded for spring tine harrow were very high in all cases (on
average ca. 7 km h-1 and 1.8 ha h-1 respectively) and definitely higher than those recorded for the
hoes. The hoes, either equipped with static or rotary tools, always worked at low speed (2.4 and 2.0
km h-1 respectively); as a consequence, their working productivity was much lower than that of the
spring-tine harrow.
156
Table 2. Work parameters of spring-tine harrowing with different tine adjustments.
Parameter
2000
2001
- 30° -15° 0° +15° mean - 30° -15° 0° +15° mean
Working depth (cm)
1.5 1.8 2.0 2.2 1.9
1.0
1.2 1.2 1.5 1.2
-1
Working speed (km h )
7.1 6.9 6.8 6.6 6.8
7.2
7.0 6.8 6.5 6.7
Working productivity (ha h-1)
1.8 1.8 1.7 1.7 1.8
1.9
1.8 1.7 1.7 1.8
0.8 0.9 1.2 1.3 1.0
0.5
0.6 0.8 0.8 0.7
Fuel cons. per hour (kg h-1)
Fuel cons. per hectare (kg ha-1) 0.4 0.5 0.7 0.8 0.6
0.3
0.3 0.5 0.5 0.4
Drawbar pull (N)
1100 1370 1780 1930 1545 750 910 1150 1250 1015
Useful power (kW)
2.2 2.6 3.4 3.5 2.9
1.5
1.8 2.2 2.3 1.9
17.6 22.0 30.8 35.2 26.4 13.2 13.2 22.0 22.0 17.6
2
5
7
10
6
1
4
7
11
6
Table 3. Work parameters of the different hoeing options.
Parameter
2000
PH
PH + TW Rotary hoe
Working depth (cm)
5.0
5.0
6.1
Working speed (km h-1)
2.4
2.4
2.0
-1
Working productivity (ha h )
0.6
0.6
0.5
Fuel cons. per hour (kg h-1)
1.1
1.5
4.9
-1
Fuel cons. per hectare (kg ha )
1.8
2.5
9.8
Drawbar pull (N)
4500
6240
Useful power (kW)
3.0
4.2
13.6
79.2
110.0
441.0
7
7
-1
PH = precision hoe, PH + TW = precision hoe + torsion weeder.
PH
5.0
2.3
0.6
1.1
1.8
4650
3.0
79.2
9
2001
PH + TW Rotary hoe
5.0
6.0
2.3
2.0
0.6
0.5
1.6
5.6
2.7
11.2
6820
4.4
15.5
118.8
504.0
9
-1
Fuel consumption was extremely low for spring-tine harrowing and did not show the
considerable increase with tine angle observed in previous experiments (Peruzzi et al., 1997). Fuel
consumption per hour of the precision hoe was low and constant over the years but, compared to
harrowing, fuel consumption per hectare was higher due to lower working productivity. Compared
to the precision hoe alone, precision hoeing + torsion weeding resulted on average in a 44%
increase in fuel consumption per hectare. Values of the PTO-powered rotary hoe were much higher
than those of the other hoes, especially for what concerns fuel consumption per hectare (as a
consequence of the low working productivity), and were higher in the second year.
Drawbar pull required by the spring tine harrow increased little from the least to the most
aggressive tine adjustment, and values were always extremely low. Values recorded for the
precision hoe were higher than those obtained in a similar experience carried out on string bean in
similar soil conditions (Raffaelli et al., 2002b). Averaged over the two years, precision hoeing +
torsion weeding resulted in a 43% increase in drawbar pull compared to precision hoeing alone.
Results of the above-mentioned parameters obviously influenced useful power and direct input.
On average, the useful power and direct input required by harrowing were respectively 2.9 kW and
26.4 MJ ha-1 in 2000 and 1.9 kW and 17.6 MJ ha-1 in 2001. It is evident that weak penetration of
tines in the soil considerably influenced these parameters. The amount of power and energy
required by the two hoes that were not equipped with elastic tools (especially the rotary hoe) was
clearly influenced by soil conditions. It is evident that the soil was hard and thus required more
energy to be tilled. The energy necessary for PTO-powered rotary hoeing was on average 4 to 5
157
times higher than that required by hoeing with static tools and, on average, it was 17 and 28 times
higher than that required by harrowing in the first and second year respectively.
It is now interesting to analyse how the working performance of these machines influenced
crop yield. In Table 4 it is possible to observe that in 2000 each working hour of the spring tine
harrow resulted in 2 and 3 times higher maize grain yield as compared to the precision and rotary
hoe respectively. Results of 2001 showed a similar trend.
The energy required to produce 1 Mg of maize yield (dry matter) was 2.6 to 3.6 MJ for springtine harrowing, 8.7 to 9.8 MJ for precision (static) hoeing, 11.6 to 16.3 MJ for precision hoeing +
torsion weeding, and 60.1 to 60.9 MJ for PTO-powered rotary hoeing (Table 4).
Table 4. Dry matter grain yield of maize per working hour of the spring-tine harrow and hoes, and
direct energy input needed to produce 1 Mg of maize grain (all the other cultural practices
were kept constant in the different treatments).
Treatments
kg h-1
MJ Mg-1
2000
2001
2000
2001
Spring-tine harrowing:
+15°
12432
9957
4.8
3.7
0°
12760
14014
4.1
2.7
-15°
13390
12178
2.9
1.9
-30°
12319
10760
2.6
2.2
mean
12725
11727
3.6
2.6
Hoeing:
Precision hoe
Precision hoe + torsion weeder
Rotary hoe
5403
5682
3668
4863
4359
4132
8.7
11.6
60.1
9.8
16.3
60.9
This study confirmed that different machines usable for mechanical weed control in a given
crop have well defined and very different characteristics, and their behaviour may change with
different soil conditions, depending on machine characteristics. Machines performance as related to
soil conditions experienced at treatment time should be taken into account more systematically in
weed control studies. These findings would help guiding the choice of the best implement to use in
any situations, especially when mechanical weed control is included in low-external input systems
that, as such, aim to reduce energy input as much as possible. In this respect, new parameters that
link mechanical and agronomic results may provide a better understanding of research outcome.
Acknowledgements
We are very grateful to R. Del Sarto, A. Pannocchia, M. Paracone, L. Pulga and S. Toniolo of
the University of Pisa for their precious cooperation in running the experiment.
158
References
BÀRBERI P. (2002) Weed management in organic agriculture: are we addressing the right issues?
Weed Research, in press.
BÀRBERI P, SILVESTRI N, PERUZZI A & RAFFAELLI M (2000) Finger-harrowing of durum
CLOUTIER D & LEBLANC ML (2000) Susceptibility of sweet maize (Zea mays L.) to the rotary
hoe: preliminary results. In: Proceedings 4th EWRS Workshop on Physical and Cultural Weed
Control, Elspeet, 20-22 March, 37.
KOUWENHOVEN JK & TERPSTRA R (1979) Sorting action of tines and tine-like tools in the
field. Journal of Agricultural Engineering Research 24, 95-113.
KURSTJENS DAG & BLEEKER P (2000) Optimising torsion weeders and finger weeders. In:
Proceedings 4th EWRS Workshop on Physical and Cultural Weed Control, Elspeet, 20-22
March, 30-32.
KURSTJENS DAG, PERDOK UD & GOENSE D (2000) Selective uprooting by weed harrowing
KURSTJENS DAG & KROPFF MJ (2001) The impact of uprooting and soil covering on the
LEBLANC ML & CLOUTIER D (2000a) Susceptibility of dry edible beans (Phaseolus vulgaris
L.) to the rotary hoe. In: Proceedings 4th EWRS Workshop on Physical and Cultural Weed
Control, Elspeet, 20-22 March, 38.
LEBLANC ML & CLOUTIER D (2000b) Susceptibility of row-planted soyabean to the rotary hoe.
In: Proceedings 4th EWRS Workshop on Physical and Cultural Weed Control, Elspeet, The
Netherlands, 20-22 March, 39.
PERUZZI A, BÀRBERI P, GINANNI M, RAFFAELLI M & SILVESTRI N (1997) Prove
sperimentali di controllo meccanico delle infestanti del frumento mediante erpice strigliatore.
In: Proceedings VI Convegno Nazionale di Ingegneria Agraria, Ancona, 11-12 September,
669-678.
RAFFAELLI M, BÀRBERI P, PERUZZI A & GINANNI M (2002a) Options for mechanical weed
control in maize – effects on weeds. In: Proceedings 5th EWRS Workshop on Physical and
Cultural Weed Control, Pisa, 11-13 March.
RAFFAELLI M, PERUZZI A & BÀRBERI P (2000) Spring-tine harrowing in sunflower and
soyabean: results of two-year trials. In: Proceedings 4th EWRS Workshop on Physical and
Cultural Weed Control, Elspeet, 20-22 March, 37-39.
RAFFAELLI M, PERUZZI A, BÀRBERI P & GINANNI M (2002b) Options for mechanical weed
control in string bean – work parameters and crop yield. In: Proceedings 5th EWRS Workshop
on Physical and Cultural Weed Control, Pisa, 11-13 March.
159
Options for mechanical weed control in string bean
– effects on weeds
D.A.G.A.E., Settore Meccanica Agraria, Università di Pisa, Italy; 2Scuola Superiore Sant’Anna,
Pisa, Italy; 3Centro Interdipartimentale di Ricerche Agro-ambientali E. Avanzi, S. Piero a Grado,
Pisa, Italy
1
Abstract
Two field experiments were carried out in 2000 and 2001 on a sandy-loamy soil to compare
different options (harrowing or hoeing) for mechanical weed control in string bean sown in 75 cmspaced rows. The first experiment included any combinations between four tine adjustments and
two treatment intensities (one or two passes) of a 3 m-wide spring-tine harrow with 6 mm-diameter
tines. The second experiment compared four different hoeing systems: (1) a PTO-powered rotary
weeder, (4) a precision hoe (as before) + torsion weeder operated with the tines crossed. Both
experiments also included a weedy check and a post-emergence herbicide treatment as references.
Weed density by species was sampled just before weed control treatments and 2 to 4 weeks after the
treatments in one fixed quadrat (100 x 50 cm) per plot. The same quadrat was used for sampling
weed biomass at string bean final harvest. In the harrowing experiment, differences among
treatments were usually negligible, likely due to low initial weed presence. Hoeing often decreased
weed density significantly, but this effect did not always turn into lower weed biomass at harvest.
Data of these experiments are not conclusive to allow ranking of the mechanical weeding
treatments based on their overall efficacy.
Introduction
Recently, integrated and organic vegetable production systems has gained a great deal of
attention by both farmers and consumers. One of the major technical problems that arise in
vegetable cropping when decreasing use of agrochemicals is weed control. This problem is often
perceived by farmers as the major constraint refraining them from widespread conversion to organic
production (Beveridge & Naylor, 1999). Farmers' request of research aimed at evaluating the
effectiveness of different non-chemical weed control methods in a range of vegetable crops is then
increasing. Non-chemical weed control may be particularly problematic in crops such as beans, that
are sown in widely-spaced rows and in which the amount of incident radiation filtering through the
canopy (and thus exploitable by weeds) during the growing season may be considerable.
This paper reports results on the effect on weeds of different harrowing and hoeing options
tested on string bean (Phaseolus vulgaris L.), one of the main spring-summer vegetables grown for
fresh consumption in Italy.
Materials & Methods
In 2000 and 2001, two field experiments were carried out on a sandy-loamy soil at the Centro
Interdipartimentale di Ricerche Agro-ambientali E. Avanzi of the University of Pisa (43°40' lat. N,
10°19' long. E) to compare different options (harrowing or hoeing) for mechanical weed control in
160
string bean. In both experiments, the soil, that hosted silage maize in 1999 and lupin in 2000 as
preceding crops, was mouldboard-ploughed at ca. 30 cm depth in winter, and later subjected to the
false seedbed technique. Mineral fertilisation was carried out pre-sowing with 120 kg ha-1 P2O5 and
120 kg ha-1 K2O. String bean cv. Delinel was sown on 7 July 2000 and 13 June 2001 at a seeding
rate of 29.6 seeds m-2 in 75 cm-spaced rows.
from –30° to +15°, where values represent the angle E between the upper part of the tine and the
perpendicular to the soil surface, see Fig. 1) and two treatment intensities (one or two passes) of a 3
m-wide Malin spring-tine harrow with 6 mm-diameter tines. The harrow was passed on 1 August
2000 and on 11 and 18 July 2001, when string bean was in the full vegetative stage. In 2000,
excessive crop size suggested not to perform the second pass.
+ JE
D
)
+15°, the arrow indicates the driving direction.
Hoeing experiment
The hoeing experiment compared four weed control implements: (1) a PTO-powered rotary
weeder (PH + TW), (4) a precision hoe (as before) + torsion weeder operated with the tines crossed
(PW + TWC). This last treatment was performed only in 2001. Hoeing was performed on 1 August
2000 and 11 July 2001.
As in the harrowing experiment, a weedy check and a post-emergence herbicide treatment
(sethoxydim 1 L ha-1, 250 L ha-1 spraying volume plus bentazone + fomesafen 0.5 + 0.5 L ha-1, 250
L ha-1 spraying volume, rates refer to commercial products) were included. In the harrowing
experiments, treatments were allocated in a split-plot design with number of passes in the main
plots and tine adjustment in the sub-plots. The hoeing experiment was laid out in a randomised
complete block design with three replicates. Size of the elementary plots was 20 m length by 3 m
width in both experiments.
Data collection and analysis
In both experiments, plant density (crop and weeds) was sampled by species just before weed
control treatments (on the same dates) and 2 to 4 weeks after treatment (on 29 August 2000 and 27
July 2001) in one fixed quadrat (100 x 50 cm) per plot, divided into an outer and inner part to
account separately for between-row and within-row weed control. The same quadrats were used for
161
sampling weed biomass at final string bean harvest (on 25 September 2000 and 6 September 2001).
The collected biomass was divided by species and placed in an oven at 80°C until constant weight.
Data presented in this paper refer to the whole quadrat size. Results on working parameters of the
different weed control treatments and on string bean yield are presented elsewhere (Raffaelli et al.,
2002).
Plant density and biomass of the total weed community and of major species were subjected to
statistical analysis. Crop and weed densities after mechanical weed control were expressed as
percent reduction as compared to initial plant density. Prior to ANOVA, data were arcsine-, square
root- or log- transformed, as appropriate (Gomez & Gomez, 1984). Treatment means were
separated by a LSD test at P d 0.05. Data shown in tables are back-transformed means. Since in
2000 it was not possible to pass the spring-tine harrow twice, the relevant data were subjected to a
randomised complete block ANOVA by taking the average of any two plots per replicate that were
subjected to the same tine adjustment as input.
Results
Percent reduction in string bean density after mechanical treatments was influenced neither by
tine adjustment nor by number of passes, being on average 11% in 2000 and 7% in 2001.
Overall, the effect of weed control treatments (both chemical and non-chemical) on weed
density and biomass was poor and nearly always non statistically significant. This lack of effect can
partly be attributed to low initial (i.e. prior to treatment) weed density in both years (on average, 16
and 18 plants m-2 in 2000 and 2001 respectively). Averaged over all tine adjustments and passes,
mean percent reduction in total weed density was 38% in 2000 and 28% in 2001.
Similarly, total weed biomass at harvest was not too high and did not significantly differ among
the mechanical treatments, being on average equal to 11.6 g m-2 in 2000 and 62.0 g m-2 in 2001
(compared respectively to 6.0 and 64.7 g m-2 with herbicide use). Slight differences were only
found in the biomass of Portulaca oleracea in 2000, which was significantly higher (P d 0.05) in
+15° (3.9 g m-2) than in any other treatments (on average 0.2 g m-2).
Hoeing experiment
On average, initial (i.e. just before weed control treatments) total weed density was
considerably higher in 2001 than in 2000 (103.9 vs. 17.8 plants m-2). In both years, the most
abundant species were Chenopodium album (which accounted for 36% and 40% of total weed
density in 2000 and 2001 respectively), Digitaria sanguinalis (36% and 17%) and Portulaca
oleracea (11% and 17%).
Except for the herbicide treatment, percent reduction in total weed density following weed
control treatments was higher in 2000 than in 2001 (Table 1). Changes in the relative ranking of
hoeing treatments between the two years did not result in statistically significant differences, likely
because of high between-plot heterogeneity. In 2000, density of C. album (the major weed) was
reduced to a greater extent by precision hoeing, PH + TW and PW + TWC (89.4% on average) than
by rotary hoeing (42.3%). However, other species (especially D. sanguinalis and P. oleracea) were
not controlled to the same extent (data not shown), thus decreasing the value of total weed reduction
obtained with the former three implements (ranging between 31.2% and 51.8%).
162
Differences among treatments in total weed biomass at string bean final harvest were found
only in 2000, when in all treatments except PH + TW values were much lower than in the weedy
check (Table 2). In PH + TW, higher total weed biomass in 2000 depended upon higher C. album
biomass.
In 2001, some significant differences in biomass were found only at the species level.
Compared to the other mechanical treatments, use of the precision hoe and PH + TWC resulted in
higher biomass of D. sanguinalis and P. oleracea respectively.
Table 1. Hoeing experiment. Percent reduction in weed density observed in string bean 28 DATa in
2000 and 16 DAT in 2001.
Chenopodium albumb
Total weeds
Treatment
2001
2000
2001
Rotary hoe
42.3 cd
97.8 a
36.3 ab
Precision hoe
92.3 ab
76.7 ab
51.8 a
PH + TW
79.8 ab
72.4 ab
47.8 a
PH + TWC
96.1 a
31.2 ab
Herbicide
72.8 bc
37.1 ab
55.8 a
Weedy check
23.8 d
14.6 b
16.1 b
a
Days After Treatment. bIn 2000 density of this species was too low to perform a reliable statistical
analysis. PH + TW = precision hoe + torsion weeder, PH + TWC = precision hoe + torsion weeder
with tines crossed. In each column, means followed by the same letter are not significantly different
at P d 0.05 (LSD test). Data shown are back-transformed means (following arcsine-transformation).
Table 2. Hoeing experiment. Dry biomass (g m-2) of the major weed species and of total weeds
observed at string bean final harvest in 2000 and 2001.
Total weeds
Chenopodium album
Digitaria
Portulaca
a
a
sanguinalis
oleracea
Treatment
2000
2001
2001
2001
2000
2001
Rotary hoe
0.0 c
24.9 ns
1.8 b
0.6 b
2.6 b
41.6 ns
Precision hoe
6.2 abc
4.6 ns
16.3 a
3.4 ab
10.4 b
95.6 ns
PH + TW
22.2 a
8.0 ns
0.2 b
0.0 b
24.6 ab
13.1 ns
PH + TWC
2.2 ns
0.6 b
32.0 a
43.1 ns
Herbicide
0.4 bc
6.9 ns
25.9 a
7.6 ab
6.0 b
58.3 ns
Weedy check
8.6 ab
4.9 ns
4.6 ab
1.9 b
107.1 a
85.5 ns
a
In 2000 density of these species was too low to perform a reliable statistical analysis. PH + TW =
precision hoe + torsion weeder, PH + TWC = precision hoe + torsion weeder with tines crossed. In
each column, means followed by the same letter are not significantly different at P d 0.05 (LSD
test), ns = not significant. Data shown are back-transformed means (following log-transformation).
Discussion
In both years, spring-tine harrowing of string bean did not result in appreciable advantages over
the control plots, but this effect was also observed for herbicide use. Similarly, no significant yield
differences were recorded among treatments (Raffaelli et al., 2002). It can be suggested that lack of
evident effects by weed control treatment may be due to overall low weed abundance experienced
in both years, likely influenced by the application of the false seedbed technique. Experiments
carried out in situations with higher initial weed presence would help to have a clearer picture of the
effect of these mechanical treatments on weeds.
163
In contrast, hoeing was always beneficial in terms of weed control, although positive effects on
crop total yield were observed only in 2000, when precision hoeing plus torsion weeding resulted in
a 16% yield gain compared to the weedy check (data not shown), despite a higher total weed
biomass at harvest. Short-term weed reduction generally appeared unrelated either to final weed
biomass or string bean yield, as were these last two parameters, suggesting that, besides the
observed selective treatment effect on different weed species, other factors (e.g. mobilisation of
nutrients driven by soil disturbance) might have played a role.
Further studies are needed to understand if one or more of the hoeing options is superior over
the others. It also remains to be seen if and to what extent a reduction in weed density such as that
observed in the hoeing experiment, although not enough to turn into a yield advantage in one
growing season, might turn into long-term beneficial effects in a crop rotation context.
Acknowledgements
The authors wish to thank all the staff of the Centro Interdipartimentale di Ricerche Agroambientali E. Avanzi, University of Pisa for their precious help in the conduction of the
experiments and sample collection and processing.
References
BEVERIDGE LE & NAYLOR REL (1999) Options for organic weed control – what farmers do.
In: Proceedings 1999 Brighton Conference – Weeds, Brighton, UK, 939-944.
GOMEZ KA & GOMEZ AA (1984) Test for homogeneity of variance. In: Statistical procedures
for agricultural research, 2nd edn, 467-471, J. Wiley & Sons, New York, USA.
control in string bean – work parameters and crop yield. In: Proceedings 5th Workshop of the
EWRS Working Group on Physical and Cultural Weed Control, Pisa, Italy, 11-13 March.
164
Preliminary results on physical weed control in processing spinach
1
F. Tei1, F. Stagnari1, A. Granier2
Dept. of Agro-environmental and Crop Sciences – University of Perugia, Italy
2
SAGIT – Unilever, Cisterna di Latina, Italy
Abstract
A field experiment was carried out in Central Italy (Tiber Valley, Perugia, 43oN, elev. 165 m)
to evaluate applicability and efficacy of some physical weed control methods in processing spinach,
sown at two different inter-row distances (0.125 and 0.25 m).
With rows 0.125 m apart, pre-sowing herbicide application (cycloate at 3635 g a.i. ha-1),
harrowing and post-emergence flaming were applied, while with rows 0.25 m apart the treatments
were pre-sowing herbicide application (same herbicide as above), finger-weeding, split-hoeing and
post-emergence flaming; untreated plots were added as checks. Physical weed control was
performed at the “4-6 true leaves” stage of the crop and at the “cotyledons” to “6 true leaves” stages
of the weeds.
Pre-sowing chemical application caused a growth reduction and, as a consequence, a delay in
harvest date in comparison with physical weed control. Flaming caused a temporary wilting of the
crop which then fully recovered, although unmarketable deformed leaves at final harvest were about
12% of total yield (on mass basis) with rows 0.125 m apart and about 7% with rows 0.250 m apart.
Finger-weeding and split-hoeing on rows 0.250 m apart, as well as harrowing on rows 0.125 m
apart, did not injure the crop.
On fresh mass basis, the percentage of weed control with rows 0.250 m apart was 97% by presowing herbicide application, 90% by flaming, 88% by split-hoeing and 64% by finger-weeding;
with rows 0.125 m apart the weed control efficacy was 82% by pre-sowing herbicide application,
30% by flaming while harrowing showed no control.
Crop yield was not affected by row distance and only slightly by weed control method.
Introduction
Scientific and public concern about the use of chemicals in agriculture has led to an increasing
interest in non-chemical weed management (Parish, 1990; Rasmussen & Ascard, 1995; Bond and
Grundy, 2001). Several investigations (Baumann, 1992; Ascard, 1995; Rasmussen, 1996; Ascard &
Bellinder, 1996; Melander, 1997, 1998; Fogelberg, 1998; Melander & Rasmussen, 2001) have
clearly shown that direct physical weed control based on mechanical and thermal methods can be
effective only if a sound cultural method is applied.
In processing spinach weed control is still mainly chemical because: 1) the mechanical harvest
needs a crop with an erect leaf posture favoured by a narrow row width (0.10 – 0.15 m); this
prevents the use of most post-emergence physical weed control methods; 2) the harvested spinach
should not contain uncontrolled weeds, considered as “pollutant bodies” in industrial processes.
In order to apply post-emergence direct physical weed control methods a wider row distance
seems to be necessary, even though negative influences on crop growth habit and competitive
ability might be expected (Fischer & Miles, 1973; Schnieders, 1999).
The aim of the present study was to investigate the applicability and the efficacy of some
physical weed control methods in processing spinach sown at two different distances between rows.
165
A field experiment on processing spinach (Spinacia oleracea L.) was carried out in central Italy
(Tiber valley, Perugia, 43°N, elev. 165 m) on a silty-clay soil with 1.2% of organic matter.
Soft winter wheat was the preceding crop and the seed bed was prepared by ploughing 0.3 m
deep, disc harrowing, rotary harrowing, spike-tooth harrowing and rolling.
The experimental design was a split block with four replicates and a plot size of about 80 m2.
Two crop inter-row distances (0.125 and 0.250 m) and different physical weed control methods
(Table 1) were compared; chemically treated and untreated plots were added as checks.
Table 1. Experimental treatments: weed control methods and inter-row
distances.
Inter-row distance (m)
Weed control methods
0.125
0.250
Chemical weed control
x
x
Harrowing
x
Flaming
x
x
Finger-weeding
x
Split-hoeing
x
Untreated check
x
x
Chemical weed control was performed in pre-sowing by applying cycloate (Ro-Neet, Siapa,
700 g L-1) at a rate of 3635 g a.i. ha-1.
Spinach cv. Tamura was sown on 12.9.2001, with a seed rate of 51 kg ha-1.
Physical weed control treatments were applied on 4.10.2001 when crop was at “4-6 leaves”
stage, broadleaved weeds were at “cotyledons” to “4-6 leaves” stage and grass weeds at “3 leaves”
to “tillering” stage.
Harrowing was carried out with a weed harrow (Pictures 1 and 2) at a working depth of 3 cm
and a driving speed of about 3 km h-1.
Post-emergence flaming was performed with a PS6 (Officine Mingozzi, Ferrara, Italy) flamer
consisting of 6 rows of gas-phase burners 0.25 m apart (Pictures 3-6). The propane consumption per
burner was 12-14 kg h-1 at a gas pressure of 0.1 MPa and at a driving speed of 2.5 km h-1. With row
width 0.25 m, burners flamed inter-row and very close to the row; with distance between rows of
0.125 alternate crop rows were fully hit by flames.
Finger-weeding close to the row was carried out with a small Kress (Tamm, Germany) fingerweeder (Pictures 7 and 8) at a driving speed of 3 km h-1.
Split-hoeing close to the row was performed with a Asperg Gartnereibedarf (Asperg, Germany)
split-hoe (Pictures 9-12) leaving 10-cm untilled strip in the crop rows, at a working depth of 5 cm
and a driving speed of 3 km h-1.
Crop was fertilised with 60 kg N ha-1, 60 kg P2O5 ha-1 and 85 kg K2O ha-1 applied at seed bed
preparation and with 92 kg N ha-1 broadcast on 4.10.2001.
The following parameters were determined: weed density just before the physical treatments
(4.10.2001) and at final harvest; weed fresh and oven dry mass (105°C for 48h) at final harvest;
crop height at final harvest; total and marketable crop yield; weed mass in the harvested spinach.
The harvest was performed on 23.10.2001 for all the experimental treatments except for the
plots chemically treated which were harvested on 2.11.2001 due to the delay of crop growth caused
by herbicide application (see Results).
166
Picture 1. Harrowing in spinach sown at rows 0.125
m apart.
Picture 2. Harrowing in spinach sown at rows 0.125 m
apart: a detail.
Picture 3. Flamer.
Picture 4. Flaming in spinach sown at rows 0.25 m
apart.
Picture 5. Flamer: a detail of the burners.
Picture 6. Flaming in spinach sown at rows 0.25 m
apart.
167
Picture 7. Finger-weeding in spinach sown at rows
0.25 m apart.
Picture 8. Finger-weeding in spinach sown at rows 0.25
m apart: a detail.
Picture 9. Split-hoeing in spinach sown at rows 0.25
m apart.
Picture 10. Split-hoe: a detail.
m apart.
m apart: a detail.
168
Results
Weed flora was mainly composed by Portulaca oleracea L.(POROL), Amaranthus retroflexus
L. (AMARE), Papaver rhoeas L. (PAPRH) among broadleaved weeds, and by Echinochloa crusgalli L. (Beauv.) (ECHCG) among grass weeds; other sporadic species were Veronica hederifolia
L. (VERHE), Chenopodium album L. (CHEAL) and Sonchus spp. Weed density, as observed just
before physical treatments (4.10.2001), was not affected by inter-row distances (Table 2).
Data about weed control efficacy of the treatments as observed at final harvest (23.10.2001) are
reported in Tables 3 and 4.
Table 2. Weed density just before physical treatments
(means over inter-row distances). Standard errors are in
parentheses.
Density (no. m-2)
Weed species
167 (33.3)
Portulaca oleracea
17 (4.2)
15 (3.6)
Papaver rhoeas
5 (1.0)
Other species
9 (1.9)
Total
213 (33.0)
Table 3. Weed density ( no. plants m-2), weed fresh and dry mass (g m-2) at crop final harvest in relation to
weed control methods in spinach sown at rows 0.125 m apart. Standard errors are in parentheses.
ECHCG
Total
4 (2.9)
-
16 (5.7)
2.0 (1.05)
Total weed
dry mass
(g m-2)
0.3 (0.16)
Chemical treatment
5 (2.3)
-
Harrowing
50 (0.1)
2 (1.5) 4 (1.6)
Flaming
26 (11.7)
1 (0.5) 2 (0.8) 2 (1.1)
2 (1.5)
-
33 (11.4)
7.9 (3.83)
0.9 (0.60)
Untreated check
60 (23.4) 5 (3.6) 12 (4.8) 1 (0.5)
3 (1.1)
-
81 (27.2) 11.2 (2.22)
1.6 (0.44)
PAPRH
VERHE
CHEAL
Total weed
fresh mass
(g m-2)
Weed control
treatments
POROL
AMARE
Weeds (no. m-2)
5 (2.1) 2 (1.5)
-
3 (1.5)
1 (0.5) 60 (22.5) 27.1 (14.70)
1.4 (0.60)
Table 4. Weed density(no. plants m-2), weed fresh and dry mass (g m-2) at crop final harvest in relation to
weed control methods in spinach sown at rows 0.25 m apart. Standard errors are in parentheses.
Weeds (no. m-2)
43 (8.9)
9.1 (2.81)
2.2 (1.13)
27 (15.5)
3.1 (1.54)
0.5 (0.27)
33 (10.7)
5.5 (1.84)
0.8 (0.30)
112 (37.9) 2 (1.5) 10 (3.5) 1 (0.7) 6 (1.3) 2 (1.5) 133 (42.3) 25.4 (8.00)
2.8 (0.87)
2 (1.5)
-
-
-
28 (5.7) 1 (0.5)
1 (0.7)
-
Split-hoeing
21 (16.0) 1 (0.5)
1 (0.5)
Flaming
32 (10.7)
1 (0.7)
POROL
-
Chemical treatment
2 (2.0)
Finger-weeding
Untreated check
-
11 (6.4) 2 (2.0)
1 (0.5) 3 (1.7)
-
TOTAL
0.1 (0.04)
ECHCG
0.9 (0.74)
AMARE
4 (2.3)
VERHE
Total weed
dry mass
(g m -2)
PAPRH
Total weed
fresh mass
(g m-2)
CHEAL
Weed control
treatments
169
Spinach showed a high competitive ability that caused a weed density reduction during the crop
growth cycle: comparing data recorded before post-emergence physical treatments (Table 2) and
that recorded in the untreated check at final harvest (Table 3 and 4), it is apparent that weed
mortality was much higher on plots with crop sown at inter-row distances of 0.125 m (62% of
mortality) than on plots sown at inter-row distances of 0.25 m (38%).
Pre-sowing chemical control gave the best weed control in terms of both density and fresh mass
and showed an efficacy of about 80% with inter-row distances of 0.125 m and 97% with inter-row
distances of 0.250 m. This difference was probably due to the higher level of soil disturbance by the
sowing machine in the case of narrower rows, which might have played a role in reducing the
residual effect of the herbicide and in stimulating weed emergence.
Taking into consideration the fresh mass recorded on untreated plots, with inter-row distance of
0.125 m (Table 3) flaming gave 30% weed control and harrowing no control; with inter-row
distance of 0.250 m, split-hoeing gave 88% weed control, flaming 78% and finger-weeding 64%.
Chemical treatment caused a reduction in spinach growth: in comparison with the physical
treatments, crop height recorded on 23.10.2002 was about 5 cm lower (data not shown) and the
harvest was delayed of about 10 days (Table 5).
Flaming caused a temporary wilting of the crop that fully recovered in few days (about 1
week), although unmarketable deformed leaves at harvest were 12% with inter-row distance of
0.125 m and 7% with inter-row distance of 0.25 m (Table 5).
Crop yield (Table 5) was not affected by the crop inter-row distance and, only slightly by the
weed control method. The physical methods gave different results in term of weed control but
slightly influenced crop yield due to high crop competitiveness. A thorough seedbed preparation
and a uniform emergence prevented the growth of the uncontrolled weeds which remained small
and under the height of harvest cutting.
Table 5. Crop height (cm), total and marketable yield (t ha-1) at final harvest in relation to weed control
methods and inter-row distance. Standards errors are in parentheses.
Chemical treatment
2 Nov.
Inter-row distance 0.125 m
Crop
Yield (t ha-1)
height
Total
Marketable
(cm)
24 (0.6) 13.2 (0.71)
13.2 (0.71)
Harrowing
23 Oct.
29 (0.8)
14.6 (1.78)
14.6 (1.78)
-
Finger-weeding
23 Oct.
-
-
-
28 (0.8)
16.5 (1.63)
16.5 (1.63)
Split-hoeing
23 Oct.
-
-
-
26 (0.6)
13.5 (1.29)
13.5 (1.29)
Flaming
23 Oct.
24 (0.7)
15.0 (0.95)
13.0 (0.84)
27 (0.9)
12.5 (0.91)
11.6 (0.63)
Untreated check
23 Oct.
29 (0.8)
16.9 (1.51)
16.9 (1.51)
28 (0.8)
14.7 (2.00)
14.7 (2.00)
Weed control
treatments
Harvest
date
Inter-row distance 0. 25 m
Crop
height
(cm)
25 (0.9)
Yield (t ha-1)
Total
12.7 (0.87)
-
Marketable
12.7 (0.87)
-
Discussion
The inter-row distance (i. e. 0.125 and 0.25 m apart) did not influence crop yield, but 0.125 m
inter-row distance prevents from the use of some mechanical weed control methods, i. e. fingerweeder and split-hoe, allowing only the inter-row harrowing that showed a poor weed control
efficacy.
With inter-row distance of 0.250 m, finger-weeding and split-hoeing showed a high potential in
direct weed control, performing with efficacy very close to the row; the high crop plant density and
competitiveness prevents intra-row weed emergences.
170
In this study post-emergence flaming was applied for the first time as direct method for weed
control in spinach and the results gave the evidence that it can be applied only when the crop is
sown with rows spaced enough (0.25 m). However, flaming gave a good weed control (about 80%),
causing just a temporary crop wilting and in some cases a permanent leaf deformity. Postemergence flaming seems to be worthy of further investigations in order to obtain a better
selectivity to the crop.
Physical methods gave a lower weed control than the herbicide treatment although yield was
not different probably due to the high crop competitiveness. In our study characterised by a prompt
and homogeneous emergence and a rapid initial growth of the crop, weeds did not determine
consistent yield losses even at high densities. Moreover, the uncontrolled weeds remained under the
height of cutting, not “polluting” the harvested product.
These preliminary results suggest that a successful weed management system in processing
spinach (granted that other cultural measures maintained the weed population at a manageable
level) should allow an initial competitive advantage for the crop in order to improve selectivity
during subsequent physical weeding operation and to reduce weed growth. To reach this aim, a
false seedbed preparation, pre-emergence flaming or very shallow harrowing, and quick and regular
crop emergence have to be provided, as found in other vegetables (see for example, Ascard, 1995;
Melander & Rasmussen, 2001; Bond & Grundy, 2001).
However, further investigations in order to verify current results, especially in presence of a
more competitive weed flora, are needed.
References
ASCARD J (1995) Thermal weed control by flaming: biological and technical aspect. PhD thesis,
Swedish University of Agricultural Sciences, Alnarp, Sweden.
ASCARD J & BELLINDER RM (1996) Mechanical in-row cultivation in row crop. In:
Proceedings Second International Weed Control Congress, Copenhagen, Denmark, 1121-1126.
BAUMANN DT (1992) Mechanical weed control with spring tine harrows (weed harrows) in row
crops. In: Proceedings 9th International Symposium on the Biology of Weeds, Dijon, France,
123-128.
BOND W & GRUNDY A (2001) Non-chemical weed management in organic farming systems.
FISCHER RA & MILES RE (1973) The role of spatial pattern in the competition between crop
plants and weeds. A theorethical analysis. Mathematical Biosciences 18, 335-350.
FOGELBERG F (1998) Physical weed control – intra-row brush weeding and photocontrol in
carrots (Daucus carota L.). PhD thesis, Swedish University of Agricultural Sciences, Alnarp,
Sweden.
MELANDER B (1997) Optimization of the adjustment of a vertical axis rotary brush weeder for
intra-row weed control in crops. Journal of Agricultural Engineering Research 68, 39-50.
MELANDER B (1998) Interaction between soil cultivation in darkness, flaming, and brush
weeding when used for in-row weed control in vegetables. Biological Horticulture and
Agriculture 16, 1-14.
MELANDER B. & RASMUSSEN G. (2001). Effects of cultural methods and physical weed
control on intrarow weed numbers, manual weeding and marketable yield in direct-sown leek
and bulb onion. Weed Research 41, 491- 508.
PARISH S (1990) A review of non-chemical weed control techniques. Biological Agriculture and
Horticulture 7, 117-137.
RASMUSSEN J (1996) Mechanical weed management. In: Proceedings Second International
Weed Control Congress, Copenhagen, Denmark, 943-948.
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RASMUSSEN J & ASCARD J (1995) Weed control in organic farming systems. In: Ecology and
Integrated Farming Systems (eds DM Glen, MP Greaves & HM Anderson). John Wiley and
Sons, Chichester, UK, 49-67..
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structure. PhD thesis, Agricultural University Wageningen, The Netherlands.
Cover crops, intercrops, mulches, manure
172
173
Impacts of composted swine manure on maize and three annual weed species
M. Liebman1, T. Richard2, D.N. Sundberg1, D.D. Buhler3, and F.D. Menalled1
1
Department of Agronomy, Iowa State University, Ames, IA, 50011, USA
2
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA, 50011,
USA
3
Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI, 48824, USA
Abstract
In recent years, water quality, odor, and cost concerns associated with conventional swine
production practices have led a growing number of farmers in Iowa and elsewhere to adopt
alternative production methods. These alternatives include the use of hoop structures that are
bedded with a deep layer of maize stalks or grain straw. Mixtures of bedding and swine manure are
easily composted and the resulting material can be spread on agricultural land as a soil amendment.
Impacts of composted swine manure on crop and weed performance are poorly understood,
however.
To address this information gap, we conducted a field experiment in which we measured the effects
of composted swine manure on soil characteristics, maize growth and grain yield, and growth and
competitive ability of three annual weed species. From 1999 through 2001, maize was grown alone
(weed-free) or in mixture with Amaranthus rudis, Abutilon theophrasti, or Setaria faberi, in plots
receiving conventional rates of synthetic fertilizer or lower rates of fertilizer supplemented with
composted swine manure. Maize production in all treatments occurred within a 3-year rotation
consisting of soybeanowinter wheat + red cloveromaize. Compost was applied at a rate of 8 Mg
C/ha preceding maize and soybean phases of the rotation and was incorporated with a chisel plow.
Weeds were sown by hand in maize rows and thinned to fixed densities.
Compost application consistently increased soil nitrate-N, K, and organic matter levels. Soil
moisture and P levels were as high or higher in plots receiving compost than in those without
compost. Compost also increased maize height, stem diameter, leaf K concentration, and stalk
nitrate-N concentration. Under weed-free conditions, maize grain yield did not differ between the
two soil amendment treatments. In contrast, compost significantly increased A. rudis height and
biomass in all three years, and increased growth of A. theophrasti in 2001. For all three weed
species, seed production was strongly correlated with biomass production. Weeds had no effect on
maize yield in either 1999 or 2000, regardless of soil amendment treatment, probably because weed
planting was delayed 8 days by wet weather in 1999, and weed emergence was slowed by dry
conditions in 2000. In 2001, maize grain yield was reduced by each of the three weed species, and
compost application exacerbated the competitive effect of A. theophrasti on maize yield. Tissue
analyses indicated that compost application greatly increased P and K levels in weeds, and that
these increases were proportionally greater than those observed for maize.
Results of this study indicate that weeds can be more responsive than maize to composted swine
manure. Amaranthus rudis was more consistently responsive to compost than were A. theophrasti
and S. faberi. Differential responses between maize and weeds to compost appear to have been
related to changes in P and K dynamics. Use of compost as a means of maintaining or enhancing
soil quality will require that effective weed management practices are in place.
174
Cover crops and mulches for weed control in organically grown vegetables
Lars Olav Brandsæter
Norwegian Crop Research Institute
Plant Protection Centre
1432 Ås, Norway
E-mail: lars.brandsater@planteforsk.no
Hugh Riley
Norwegian Crop Research Institute
Apelsvoll Research Centre division Kise
2350 Nes på Hedmark, Norway
E-mail: hugh.riley@planteforsk.no
Abstract
Cropping systems for organic vegetable production should function with respect to both crop
protection and plant nutrition. The use of living cover crops, such as white clover in cabbage, has
shown promising results in relation to both weed and pest control. However, competition for
nutrients and water is a main obstacle in such systems. To avoid competition, we have focussed on
three different approaches in our experiments: A) The synchronisation of a cover crop with the
onset of maximum vegetative growth of the vegetable crop. B) The establishment of a winter
annual or biennial legume, of erect growing habit, during the first year, followed by mowing the
legume in spring before transplanting vegetables into the mulch. C) The use of chopped mulch
material obtained from a green manure crop elsewhere in the rotation, in sown or transplanted
crops. For the first approach, Sub-clover (Trifolium subterraneum L.) shows favourable growth
characteristics. However, cultivars with sufficient winter survival ability for Norwegian conditions
were not found in our experiments. For the second approach, screening experiments have shown
that the winter annual legume Hairy Vetch (Vicia villosa Roth.) and the biennial legume Yellow
Sweet Clover (Melilotus officinalis (L.) Pall.) are probably the most promising species. Preliminary
results, from experiments in which cauliflower was transplanted into a mulch of mown Hairy
Vetch, showed that the green manure effect of this species was better when incorporated into the
soil than when used as a surface mulch. For the third approach, the use of clover/grass material as a
surface mulch in carrots, red beet and white cabbage has given good control of annual weeds, but
not of perennials. It is difficult to quantify the amount of clover material needed for sufficient weed
control in different vegetables. However, our experiments have shown that the following amounts
may be appropriate: 6, 9 and 12 tonnes DM ha-1 for white cabbage, red beet and carrots,
respectively. From a holistic point of view; the use of clover material has also given promising
control of pests, especially in carrots, as well as having substantial nutritional value when used as
either green manure or mulch.
175a
The role of cover cropping in renovating poor performing paddocks
F.C. Hoyle
Department of Agriculture, Centre for Cropping Systems, Western Australia
Key messages
•
•
•
•
•
Cover crops (green manure crops) can be used as a tool in an IWM strategy, particularly where
herbicide resistance is an issue
Legume crops used in renovating paddocks (green manure, brown manure, green mulch) can
improve grain yield and protein significantly
Benefits on heavy soils can be maintained in the medium term following renovation
Crop type significantly influences suitability for renovation cropping
Data indicates green mulching and brown manuring may be used as an alternative to green
manuring on soils prone to erosion, in no till farming systems or in maintaining soil structure
Introduction
The development of renovation cropping techniques in Western Australia is primarily aimed at
rejuvenating poorer performing areas of the farming system, where the viability and continuing
production of grain crops is at risk due to limitations imposed by physical, biological or chemical
constraints. This system will be developed to use a variety of management tools, such as green
manure crops to provide an integrated approach to improving the long term viability of farming
systems.
The value of legumes in crop rotations is evident in Western Australian farming systems, where
diversified rotational sequences incorporating these plants have resulted in higher contributions of
mineral nitrogen to the soil. High biomass legume and pulse crops act as a ‘break’ crop in disease
and pest cycles, allow effective grass control and rotation of herbicide groups in the farming
system. Where the production of conventional legume crops is limited by soil type and growing
conditions, other options such as the use of ‘phase’ pastures may provide an alternative solution to
improving chemical fertility. Pasture species such as French Serradella 'Cadiz' can provide
attributes such as soft seededness, high biomass production in a single year and may be integrated
with sheep management where required.
One of the primary factors in adopting a green manure phase is to combat the risk of
developing herbicide resistance or, as a tool in managing populations where resistance has already
been identified. A green manure phase, if managed properly, should result in 100% seed set control
of weeds. Combined with integrated management options such as delayed seeding of the wheat
phase, application of an early knockdown, high seeding rates and seed catching in rotation with a
canola crop, growers are able to approach the problem of resistance with a number of different
mechanical and herbicide options.
175b
Definitions
For the purpose of this paper, cover cropping refers to the growing of a crop with the principle
aim of incorporating or returning it to the soil. This method has been used in the past by growers in
Western Australia, and is experiencing renewed interest as a tool to increase organic matter;
improve the physical, biological and chemical properties of soil and as an integrated weed
management tool.
Conventional 'green manuring' involves the incorporation of green plant residue into the soil,
by either discing or ploughing. ‘Brown manuring’ refers to desiccation of the crop and is most often
used on soils prone to erosion. Mowing or slashing of a crop is referred to as ‘Green mulching’,
plant residue left on the soil surface to maintain soil moisture by reducing evaporation.
Aim
This research project aims to evaluate appropriate crop types and incorporation techniques
suited to a Mediterranean environment, and quantify their influence on grain yield and quality, soil
health and weed populations.
A range of crops is being evaluated for potential as 'cover crops' under different environmental
conditions in the wheatbelt of Western Australia. Species include a number of grain legume crops
(eg. field peas, Lathyrus spp.), cereals (eg. oats), brassica (eg. mustard and canola), pasture species
(eg. Cadiz, Biserrulla) and mixes of species. Treatments consisted of green manuring (ploughing),
green mulching (slashing) and brown manuring (chemical dessication), imposed at anthesis.
Grain yield and quality measured on wheat and canola grown in rotation with cover crops,
provide an initial estimate of likely benefits or loss. Physical and chemical soil characteristics such
as water infiltration, available nitrogen and organic carbon are also taken on a limited subset of
treatments. Sites established to investigate integrated weed management options include baseline
surveys of weed populations and above ground population dynamics. Many of these sites are
maintained for a minimum of two cropping phases to assess economic viability and medium term
benefits.
Case Study: 00WH63 (Bindoon, loamy sand)
This trial was established at Bindoon in Western Australia, on a loamy sand pH4.8 in CaCl2 to 10
cm-1 and increasing at depth. The site chosen was established to be responsive to nitrogen and had
an organic carbon of 4.9 per cent at the surface.
A number of crop treatments (field peas, mustard, lupins, oats) were sown in a randomised
block design with three replicates. Three spring manipulation treatments were imposed within each
plot (green manure, brown manure, green mulch) approximately 20 m in length and 3 m in width,
the exception being the control plots which were taken to harvest in 2000. Crops were sown at 100
kg ha-1 for the peas and lupins, 150 kg ha-1 for the oats and 8 kg ha-1 for the mustard treatments on
the 23rd June. Plots received 140 kg ha-1 DAP (18%N, 20%P, 1.7%S), 70 kg ha-1 of which was
banded below the seed and 70 kg ha-1 of which was drilled with the seed.
A non-selective was applied on the same day as seeding, and a selective herbicide applied
approximately 20 days later. The manure treatments were imposed on 11th October 2000, following
rain.
175c
Results
2000
Oats and mustard had significantly lower tissue nitrogen than the legume crops tested, although
high biomass production contributed to a high nitrogen input overall in 2000 (Table 1). The
legumes contributed similar amounts of nitrogen but produced a significantly lower biomass, which
would have advantages in stubble handling for the following growing season.
Table 1. Plant attributes of four renovation crops grown in 2000 at Bindoon on a loamy sand
Field peas
Mustard
Oats
Lupins
LSD (P=0.05)
Ryegrass no. (plants/m2)
195
224
194
224
NS
Tissue N%
2.2
1.4
1.2
2.9
*
Crop DM (t/ha)
6.3
16.3
20.5
4.4
2.5
2001
It is apparent in Figure 1 that nitrogen uptake by the wheat crop is higher during early growth for
the manured treatments when compared to the harvested control (peas), potentially indicating a
greater availability for treated plots.
Plant tissue N (%)
Figure 1. Tissue N % in wheat tops sampled at Bindoon, Western Australia on a loamy sand after
renovation techniques imposed in 2000. Data is the average of all treatments. LSD
(P<0.001), date*crop=0.27, crop=0.1, date=0.16
6
5
4
3
2
1
0
8-Jun
Oats
Peas
Peas (H)
28-Jul
16-Sep
5-Nov
25-Dec
Date sampled
Significant gains in wheat grain yield and protein have been observed in this trial (Fig 2).
175d
2.5
2.0
1.5
1.0
0.5
0.0
11.5
11
10.5
10
9.5
9
Harvest Lupins Mustard Oats
(Field
pea)
2000 Treatment
Grain protein %
Grain yield (t/ha)
Figure 2. The effect of renovation crop treatments imposed in 2000 on grain yield and quality of
wheat cultivar ‘Carnamah’ in 2001, at Bindoon on a loamy sand. Data is the average of
all treatments. LSD (P<0.01), grain protein=0.3, grain yield=0.14.
Field pea
Protein %
At this site, no significant differences in grain yield and protein (Fig 3) were observed for different
incorporation techniques such as green manuring, brown manuring and green mulching in this trial
(single site, single season). All 'manured' field pea treatments were significantly higher in both grain
yield and protein than harvested field peas (Fig 3).
2.5
11.5
2.0
11
1.5
10.5
1.0
0.5
10
0.0
9.5
Harvest
Green
Brown
manure
manure
2000 treatment
Green
mulch
Grain protein (%)
Grain yield (t/ha)
Figure 3. The effect of field pea treatments imposed in 2000 on grain yield and quality of wheat
cultivar ‘Carnamah’ in 2001, at Bindoon on a loamy sand. LSD (P<0.01), grain
protein=0.6, grain yield=0.21.
Grain yield (t/ha)
Protein (%)
The influence of manure treatments on weed populations (radish and ryegrass) is consistent across
all crops, with no significant difference between green manuring, brown manuring and green
mulching (data not presented). Field pea treatments presented in Figure 4, indicate significant
control of background ryegrass and radish populations is also achieved.
175e
Figure 4. The effect of field pea treatments imposed in 2000 on radish and ryegrass numbers in
2001, at Bindoon on a loamy sand. In 2000 average weed number was 206 plants/m2.
Ryegrass
number
(plants/m2)
160
120
LSD (P=0.05)
80
40
0
Harvest
Green
manure
Brown
manure
Green
mulch
Treatment imposed in 2000 on field
pea
Discussion
These results should be viewed in the context of data presented from a single site in a single
season. Seasonal and spatial variability will influence potential benefits and further economic
analysis is required.
The biomass and associated nitrogen content of a crop provides a key for growers in
determining which species will provide the greatest potential for yield improvements. Time should
be spent considering the primary limiting factors, as different crops may be chosen for building soil
organic matter, weed competition, nitrogen or stubble handling during seeding.
Although these data show significant gains can be achieved, a lack of prolonged benefits in
other trials on lighter textured soils (data not presented) indicates medium term productivity gains
may largely be associated with heavier soil types (sandy loam, loam, clay loam). Therefore if a crop
fails in the year after a manure phase, it is likely a significant proportion of the benefits may also be
lost. A similar trial on a heavier soil at this site (data not presented) yielded approximately 15-20%
higher when green manure treatments were compared to a control, and must therefore yield and
quality benefits must be maintained for longer to be economically viable.
The cost of a green manure phase is largely associated with the loss of income required to grow
and subsequently ‘sacrifice’ a crop in a Mediterranean type environment. There is a highly variable
risk often associated with the implementation of a green manure phase (Moerch and Bathgate,
2000), the primary benefits likely to be associated with nitrogen recovery. Recovery of nitrogen
following a green manure crop is likely to vary due to soil type, environment, crop type or
management; quality and yield potential realised dependent on the percentage of residue
decomposed (Badaruddin and Meyer, 1990).
The adoption of green manure crops may be most profitable where a ‘tactical’ approach is
taken, such as in response to a seasonal event or disease outbreak, where the costs involved are
minimal and is likely to provide most benefit in Western Australia. Initial analysis suggests this
may occur in a low-income year (low yield potential) or where a crop fails (Moerch and Bathgate,
2000). Strategic use of manure crops may be employed together with other management options
where problems exist that have resulted in a yield decline of 20% or more (Moerch and Bathgate,
2000) and represent part of a long-term systems approach to resolving specific issues. These types
175f
of strategies would be appropriate for sites where large weed populations are present, or herbicide
resistance restricts the management of weeds through chemical application.
In paddocks with herbicide resistant populations, management may preclude the use of
selective herbicides. Delayed seeding, enabling the effective use of knockdown herbicides, provides
an ideal start for a quick growing, high biomass crop (high vigour) crop able to compete effectively
against further weed germinations. Combined with rotational management strategies, high seed
rates, tillage practices and appropriate herbicide use, it is possible to realise significant reductions in
weed numbers.
Virtually any crop or pasture can be utilised as a green manure, but to maximise gains to the
following cropping phase, they should be managed to produce a maximum amount of biomass and
manured at, or soon after flowering. Soil type must be considered when making decisions on the
method of renovation. Lighter soils at risk of erosion should be treated with care, and green
mulching or brown manuring may be preferable options in this situation.
Acknowledgements
I would like to acknowledge Judith Devenish and James Bee for the technical support provided
to this project and the provision of a site by the Bindoon Catholic Agricultural College. This trial
was established and maintained by the Wongan Hills Research Support Unit, WADA. I would also
like to acknowledge the funding base provided by the Department of Agriculture and the Grains
Research and Development Corporation (GRDC).
References
BADRUDDIN, M. AND MEYER, D.W. (1990). Green-manure legume effects on soil nitrogen,
grain yield and nitrogen nutrition of wheat. Crop Science, 30, 819-825.
MOERCH, R AND BATHGATE, A. (2000). An economic analysis of renovation cropping.
Economic Series 99.10. Policy and Economics Group, Department of Agriculture Western
Australia.
176
Managing intercrops to minimise weeds
H.C. Lee & S. Lopez-Ridaura
Imperial College, Department of Agricultural Sciences, Wye, Ashford, Kent TN25 5AH, UK
Abstract
A field experiment is described which investigates possible relationships between a wheat-field
bean intercrop and associated weeds. Intercrop and sole crop canopy light interception was
monitored and compared with both intercrop and weed biomass yields. The intercrop treatments
were generally associated with reduced weed biomass. The tentative conclusion was that weeds
were inhibited by the interaction of at least several factors: competition for light, soil moisture and
perhaps other non-measured factors. The relevant literature is reviewed and it is concluded that
further work is needed to try and understand the key factors leading to weed inhibition in intercrops
and how these factors might interact.
Introduction
When two plants grow near to each other, it is known that they are likely to compete for
environmental resources (Vandermeer, 1990) and that this competitive interaction is liable to be
changed by factors such as nutrient status, water availability and degree of shading (Harper, 1977).
The same competitive relationship is likely between individuals of different species, including crops
and weeds, though this can also lead to facilitation (enhancement of conditions for an individual of
one species by the activities of another) (Vandermeer, 1990).
When crop-weed interactions are therefore examined, it is no surprise that weed biomass tends
to decrease as crop density increases (Lawson & Topham, 1985) and vice versa (Malik et al., 1993).
Indeed, the choice of crop species and their rotation was a key method of weed management prior
to the advent of herbicides (Walker & Buchanan, 1982) and continues to be so on organic farms
(Lampkin, 1990). This competitive interaction has also been shown to be true between weeds and
intercrops (Mohler & Liebman, 1987).
In general, many studies of intercrops report that they tend to be associated with reduced weed
biomass compared to the respective sole crops (Akobundu & Okigbo, 1984; Fujita et al., 1992;
Hosmani & Meti, 1993; Koster et al., 1997; Ghanbari-Bonjar & Lee, 2002a&b). This seems
generally to be due to a greater utilisation efficiency of resources (especially light, water and
nutrients) by intercrops (Willey & Osiru, 1972; Reddy & Willey, 1981; Abraham & Singh, 1984;
Unamma et al., 1986; Fukai & Trenbath, 1993).
This paper presents data for one field experiment, which monitored the light environment in a
wheat-field bean intercrop. Results from other researchers are also reviewed, to try and understand
potential interactions of competitive factors and formulate general conclusions.
177
One field experiment was carried out on the Prescott field of Imperial College farm at Wye,
Kent, UK (51o 11´N, 0o 57´E, altitude 40-50 m above sea level). The field experiment was
conducted during the spring and summer of 1997. The soil series was a well-drained calcareous silt
loam of pH 8.0 and with 4.5% organic matter content. The average chemical concentrations of N,
P, K Ca and Mg were 2.1, 40.2, 175.7, 3153.2, and 61.4 mg/kg, respectively. The experimental site
had previously been used for a commercial crop of forage maize. No herbicides were applied during
the experiment.
The treatments were compared in a split plot design with harvesting times as the main plot, and
cropping system as the sub plot. For both experiments the densities of wheat and beans are
expressed as percentages of their recommended drilling rates (RDR), sole crop densities being 480
(192 kg ha-1) and 48 (235 kg ha-1) seeds m-2, respectively. Inter-row spacing was 17 and 34 cm in
the sole crops of wheat and bean, respectively. Alternate row intercrops of wheat and bean, were
used with an inter-row spacing of 17 cm. Bean was planted first at a depth of 7 cm with a
Pneumasem vacuum drill, and then wheat at 3 cm depth with a Hege plot drill. All plots were 12 m
long by 2 m wide and were drilled longitudinally.
The spring wheat variety Chablis and bean variety Victor were used. There were three harvest
dates as main plots when the sole wheat reached (H1) growth stage 67 (Zadok et al., 1974) and bean
growth stage 72 (Stulpanagel, 1984) (15 June), (H2) wheat stage 75 and bean stage 78 (15 July) and
(H3) wheat stage 87 and bean stage 85 (30 July). At H1, H2 and H3 crop and weed biomass were
assessed. H1, H2 and H3 equated to sole wheat dry matter (DM) contents of 30, 45 and 60%,
respectively. At each harvest date four treatments were nested, of which two were sole crops and
two were intercrops. The two sole crops of beans (B) and wheat (W) were grown at 100% RDR.
The two intercrop treatments were 100% RDR bean-50% RDR wheat (Bw) and 50% RDR bean100% RDR wheat (bW). The experiment was drilled on 11 March 1997.
One-metre long, cylindrical thermocouple solarimeters (Szeicz et al., 1964) were assembled at
Imperial College, Wye and calibrated using a commercial Kipp (Kipp and Zonen, Netherlands) as
standard. Collection of light interception data in the field used a Delta ‘T’ Data-Logger, measuring
every minute and condensing data as an average every hour. This was done on three dates in 1997:
31 May, 12 June and 24 June between 05.30h and 20.30h. Crop and weed biomass harvest dates did
not coincide with those for light measurements due to a shortage of labour.
Results
The major weed species were Polygonium aviculare, Fumaria officinalis, Galium aparine,
Ranunculus repens, Papaver rhoeas, Capsella bursa-pastoria and Rumex spp. for all treatments.
Total monthly rainfall for the experimental period was: June = 135.4mm; July = 37.0mm. Light
interception was greatest for Bw on 31 May, but that for B was largest for the latter two dates,
though Bw was similar (Table 1). Both B and bW showed a relatively large weed biomass on 15
June but these decreased at later dates (Table 2). By comparison, W and Bw showed smaller
biomasses of weeds throughout the experiment and Bw also gave the largest crop biomass yields of
all treatments.
178
Table 1. Percentage of light intercepted, averaged between 05.30h and 20.30h (no error values
available).
Date
B
W
Bw
bW
31 May
62.5
59.6
73.8
70.0
12 June
79.3
56.2
77.8
67.3
24 June
86.7
60.2
85.0
74.6
treatment key: B = sole bean; W = sole wheat; Bw = 100% RDR bean, 50% RDR wheat;
bW = 50% RDR bean, 100% RDR wheat.
Table 2. Crop and weed biomass yield (t ha-1).
H1
15 June
H2
15 July
H3
30 July
SEDs:
Crop biomass
Weed biomass
Crop biomass
Weed biomass
Crop biomass
Weed biomass
B
2.85
1.62
7.65
1.31
10.27
1.25
W
3.95
0.16
7.35
0.09
6.57
0.10
Bw
4.90
0.24
9.80
0.38
10.30
0.38
bW
4.35
2.00
9.65
0.51
9.20
0.20
Crop biomass harvest dates = 0.23; Cropping treatments = 0.28
Weed biomass harvest dates = 0.14; Cropping treatments = 0.11
treatment key: B = sole bean; W = sole wheat; Bw = 100% RDR bean, 50% RDR wheat;
bW = 50% RDR bean, 100% RDR wheat.
Discussion
So, what is the relationship between crop and weeds for the above data? Sole bean had the
largest weed problem, but this declined during the experiment and bean yield improved in July
despite the drier soil. All other treatments were associated with generally lower weed biomasses
throughout. The only exception, bW in June, may have been anomalous and due to site variation.
The rapidly drying soil in July may have led to competition for soil moisture between crops and
weeds. It is therefore possible to hypothesise that light interception and shading of weeds may have
interacted with that of competition for soil moisture. However interpretation is further complicated
by the sole wheat treatment, which intercepted only about 60% of incoming light throughout the
experiment. Later in the experiment, when soils were drier, this could be expected to be due to
competition for soil moisture. However in June, when there was adequate soil moisture available, it
does not seem likely that weeds suffered excessive competition with wheat for light or water. The
relatively lower weed biomass in June in sole wheat might therefore have been due to some other
inhibition not measured here. Thus, there seems to be evidence of the interaction of at least several
factors affecting the incidence of weeds in this experiment: light, soil moisture and perhaps other
factor(s) that have not been identified.
Light
Some researchers refer to intercrops in terms of their ability to ‘smother’ weeds (Akobundu &
Okigbo, 1984; Zuofa et al., 1992) whilst many others specifically refer to competition for light
(Keating & Carberry, 1993; Carsky et al., 1994; Olasantan et al., 1994; Srivastava & Srivastava,
1996; Maina & Drennan, 1997; Maina, 1997; Rana & Mahendra Pal, 1999). For the data reported in
this paper, competition for light might not have been the only factor, as discussed above. Below-
179
ground competition of roots for moisture may have also been important. Root development and the
ability to compete for water is well known to be important for sorghum/groundnut intercrops
(Azam-Ali et al., 1990) and other cereal intercrops such as maize/pea competing against weeds,
especially in drier conditions (Semere & Froud Williams, 1997). Morris and Garrity (1993a) review
earlier work and conclude that many intercrops exhibit greater water use efficiency (WUE) than
respective sole crops, though shading within intercrops can alter the vigour of some low-growing
legumes and reduce this factor (Eriksen & Whitney, 1984).
Nutrients and water
Competition for nutrients is also important between weeds and intercrops. For instance, weed
biomass has been analysed for nutrient concentrations within sole maize crops (Morrish, 1995) and
those intercropped with cowpea (Ayeni et al., 1984) and shown to contain close to twice that found
in the maize crop. This ability of many weed species to take up proportionately greater amounts of
nutrients from the soil may be due to comparatively finer root systems. This is shown when
comparing crops: for example, the ability of barley to take up more phosphorus and potassium than
field beans when intercropped (Martin & Snaydon, 1982). In that case, the lower biomass but finer
root system of the barley appeared more efficient than that of the field bean. However, the growing
seasons of these experiments (1977 and 1978) did not suffer from any prolonged drought, as shown
by rainfall data in that paper. Thus it can be suggested that crops (or weeds) with smaller, finer root
systems can benefit from more efficient nutrient uptake when soil moisture is favourable. However,
any prolonged drought may lead to the dominance of the ability to take up soil moisture, which will
favour crops (or weeds) with deeper rather than finer rooting systems. An additional factor might
be that of facilitation, since root exudates from some plants are known to increase the availability of
P in soils. Thus Morris & Garrity (1993b) report that white lupin led to increased P uptake by wheat
and that pigeon pea similarly benefited sorghum.
Time of weed emergence and allelopathy
In addition to the classic competition factors discussed above, there are several others, which
are less reported but still potentially significant. Time of weed emergence is well known to be
important. It is the main reason why organic autumn-drilled crops are usually planted later
(October/November) than conventional (September/October), to avoid the known flush of weed
emergence in September (Lampkin, 1990). Some research with intercrops has shown that
component species may show an alteration in their critical period for potential weed interference.
For example, research has suggested that yam intercropped with maize is much more sensitive to
early competition with weeds (from three weeks after planting) than corresponding sole yam
(Orkwor et al., 1994). Thus, some intercrops may actually increase the susceptibility of at least one
intercrop component to weed interference. Another rather more controversial aspect of plant
interaction is allelopathy. Some agronomists argue that allelopathy can be important (Walker &
Buchanan, 1982), whilst others argue the opposite: for a good review, see Inderjit & Keating
(1999). Mohler & Liebman (1987) who worked on barley-field pea, suggested that the relative
dominance of barley might have been partly due to its allelopathic inhibition of the field pea,
similarly supported by other work (Overland, 1966). Caamal-Maldonado et al.,(2001) have studied
several legume crops (velvet bean, jumbie bean and jack bean) as cover crops with potential
allelopathic effects against weeds. Is allelopathy therefore a relatively widespread factor in crop
weed interactions? Further research at Wye will be investigating the possibility during 2002 and
thereafter.
180
Interaction of factors
The final point to consider is a holistic one: intercrops may compete with weeds due to the
interaction of several or even all of the above factors considered, with the relative importance of
each factor depending upon stage of growth, soil conditions, weather and also crop genetic
(cultivar) characteristics. Some work considers the potential interaction of factors, such as light and
water for cotton-velvetleaf intercrops (Salisbury & Chandler, 1993) and interactions of light and
nitrogen for pea-barley intercrops (Jensen, 1996). However there is very little other similar work in
the literature. As a conclusion, it is suggested that more needs to be done to investigate the relative
importance of competition factors between intercrops and weeds. We need to understand if some
factors are more important than others and how choice of genotype and variations in environment
(especially weather and soil conditions) might affect intercrop-weed competition. Work so far
clearly indicates the potential for intercrops to reduce the incidence of weeds within farming
systems without resort to herbicides and this useful attribute should be explored further. However,
this is easy to state here but may prove technically challenging to undertake in the field. At Wye
this will be a priority for our research on intercrops over the next years.
References
ABRAHAM C.T. & SINGH S.P. (1984) Weed management in sorghum-legume intercropping
systems. Journal of Agricultural Science, Cambridge, 103, 103-115.
AKOBUNDU I.O. & OKIGBO B.N. (1984) Preliminary evaluation of ground covers for use as live
mulch in maize production. Field Crops Research, 8, 177-186.
AYENI A.O., AKOBUNDU I.O. & DUKE W.B. (1984) Weed interference in maize, cowpea and
maize/cowpea intercrop in a subhumid tropical environment. II. Early growth and nutrient
content or crops and weeds. Weed Research, 24, 281-290.
AZAM-ALI S.N., MATTHEWS R.B., WILLIAMS J.H. & PEACOCK J.M. (1990) Light use,
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183
Impact of composted swine manure on crop and weed establishment and growth
Fabián D. Menalled, Matt Liebman, and Douglas D. Buhler
308 National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011-4420
E-mail: menalled@nstl.gov
Abstract
Composted swine manure represents a promising approach to recycle waste products and improve
soil fertility. However, little is known about how this and other soil amendments affect soil-cropweed interactions. We conducted a series of experiments to evaluate the influence of compost on
crop and weed germination, seedling emergence, growth, and competitive ability.
Laboratory Bioassay Experiments. Three crop species (corn -Zea mays-, soybean -Glycine max-,
and wheat -Triticum aestivum-) and three weed species (giant foxtail -Setaria faberi-, velvetleaf Abutilon theophrasti-, and common waterhemp -Amaranthus rudis-) were chosen to assess the
effects of compost on germination and early growth. For each species, seeds were placed in
moistened germination paper with 100 g of soil containing the equivalent of no compost (0g
C/cm2), low compost (0.485g C/cm2), medium compost (0.97g C/cm2), or high compost (1.455g
C/cm2). After 4 days of incubation, number of germinated seeds and root length were measured.
Compost reduced germination and root length of all species. Three patterns were detected when
relative values [(control–compost amended)/control] were regressed against ln(seed weight). First,
compost did not affect root length, but reduced germination. Second, the inhibitory effect on
germination increased with compost concentration. Finally, compost's inhibitory effect declined
with seed size.
Greenhouse Study. To understand the impact of organic soil amendments on establishment and
growth we used the species and compost concentrations described above. Species were sown in
pots and emergence was determined every 3-5 days. The first 4 emerging plants were marked and
allowed to grow. At 18 and 39 days after planting we measured basal diameter, height, leaf area,
and biomass. Compost did not affect emergence of any of the three crops, but reduced total
emergence in two of the three weed species: velvetleaf and common waterhemp. In the no-compost
treatment, relative growth rate (RGR) and leaf area expansion rate (LAER) were similar among the
6 species. However, weeds had significantly larger RGR and LAER than crops in the medium and
high compost treatments.
Field Experiment. This study assessed the impact of compost and tillage on crop-weed
interactions. We selected 8 no-tillage and moderate-tillage soybean plots (7.6 m by 13 m) with
compost added at a rate of 8 103 kg C/ha, or without compost. In each plot, 5 experimental units
were assigned to the following treatments: 1) common waterhemp sown at soybean planting, 2)
common waterhemp sown at soybean emergence, 3) common waterhemp sown at soybean secondnode stage, 4) common waterhemp sown at soybean sixth-node stage, and 5) weed-free soybean.
Plant diameter and height were measured periodically and biomass at the end of the growing
season. In all studied situations, common waterhemp sown at planting reduced soybean stem
diameter. In tilled plots where common waterhemp was excluded until the second-node stage,
compost increased soybean diameter. These results, together with those from the laboratory and
greenhouse studies, indicate that compost reduces weed emergence, but increases weed competitive
ability. Therefore, compost applications should be done within the context of an effective
integrated weed management program.
184
A system-oriented approach to the study of weed suppression by cover crops
and their residues
A.C. Moonen & P. Bàrberi
Scuola Superiore Sant’Anna, Pisa, Italy
Abstract
This paper aims to propose and discuss a system approach to study weed suppression by cover
crops and their residues, including research in allelopathy, in order to predict long-term effects of
these interactions that could eventually be turned into practical management advice. Three possible
cover crop-weed interaction mechanisms have been identified: (1) the suppression effect of autumnsown cover crops on weed populations establishing in the cover crop, (2) the weed suppression
effect of cover crop residues on the weed population developing in the cash crop following the
cover crops and (3) the residual effect on weed seedbank size and composition present in the next
winter cash crop. All three mechanisms will be studied by observations in a field trial and by
‘nature-simulating’ laboratory and glasshouse experiments.
Introduction
Biochemical interactions among plants have been described for natural (Souto et al., 2000) as
well as agricultural ecosystems. In agricultural systems, allelopathic substances released by residues
of certain crop species can help suppress weed species. To improve this effect, several studies have
been carried out on the use of cover crops to maximise weed suppression by allelopathic interaction
(Masiunas et al., 1995; Lehman & Blum, 1997). Living cover crops exert a weed suppression
capacity mainly through resource competition, while the mulch layer left on the soil surface or the
residue incorporated in the soil after cover crop destruction result in changed soil physical
conditions (Teasdale & Mohler, 1993). Besides a physical effect, the decaying residue may release
allelopathic substances. Both factors influence weed seed germination and seedling early growth.
However, the relative contribution of alteration of the physical environment and allelopathy to
cover crop residue – weed interactions still has to be clarified. The natural substances that can cause
allelopathy are secondary compounds released by microorganisms during plant decomposition or
leached by roots or leaves. The most frequently found compounds belong to the group of phenolic
acids and include benzoic and cinnamic acids, coumarins, tannins, flavonoids, terpenoids, alkaloids,
steroids and quinones. Allelopathic inhibition is caused by combined action of these compounds
rather than by one single compound (Einhellig & Leather, 1988). Whether or not allelopathic
inhibition will take place depends, besides the presence of the compounds in the soil, on soil factors
like temperature, pH, humidity and nutrient status (Stowe & Osborn, 1980; Mwaja et al., 1995) and
on weed species sensitivity (Weston et al., 1989; Burgos & Talbert, 2000).
Research on allelopathy is often criticised because proof of its existence in nature is considered
insufficient. The six criteria, established by Willis (1985), that have to be confirmed in order to be
able to conclude that allelopathy is actively present in the field have never been fully implemented.
However, many researchers have attempted to give circumstantial evidence of the existence of
allelopathy in the field by using Koch’s postulates, developing model systems and applying the
concept of density-depended phytotoxicity in order to distinguish resource competition from
allelopathic interactions in controlled laboratory and greenhouse experiments. Although evidence of
allelopathic interactions coming from laboratory bioassays can only suggest the possibility of its
185
existence in the field and cannot supply full prove of it, they can be very useful to increase the
understanding of the mechanisms involved (Blum, 1999). Bioassays should be combined with field
experiments because the information on phytotoxic compound concentration present in the plant
tissue, debris or extracts is only useful in combination with knowledge about the characteristics of
the environment, including the rhizosphere (Blum et al., 1999).
The aim of this paper is to propose and discuss a system approach to study weed suppression
by cover crops and their residues, including research in allelopathy in order to predict long-term
effects of these interactions that could eventually be turned into practical management advice. Such
an approach is based on field observations in combination with controlled glasshouse and
laboratory experiments under ‘natural’ conditions in order to determine the mechanisms responsible
for the interactions between cover crops and weeds. Three possible cover crop-weed interaction
mechanisms have been identified (Fig. 1): (1) the direct suppression effect (mainly exerted through
resource competition) of autumn-sown cover crops on weed populations establishing in the cover
crop, (2) the weed suppression effect (by changing the physical characteristics of the soil or through
allelopathic interactions) of cover crop residues on the weed population developing in the cash crop
following the cover crops (grain maize) and (3) a residual effect on weed seedbank size and
composition present in the next winter cash crop (durum wheat). Therefore weed population
sampling in the field will be carried out in the winter cover crop, in the following maize crop and in
the winter durum wheat crop. To try to explain the weed population patterns observed in the field,
glasshouse and laboratory experiments will be set up to identify if allelopathic interactions can be
present in the field, if nitrogen fertilisation level can influence this effect and what can be the
potential effect in the long run on the weed community composition.
POTENTIAL WEED SUPPRESSION MECHANISMS OF COVER
CROPS
Mechanism 1
Weed suppression by living cover crop:
resource competition.
Mechanism 2
Weed suppression in the following crop by cover crop
residue:
change of soil physical characteristics and allelopathy.
Mechanism 3
A long-term weed suppression effect in crops
with the same growing-season as the cover crop:
seedbank depletion.
Fig. 1. Potential cover crop-weed interaction mechanisms
The study will be carried out in a long-term field experiment that has been set up in 1993 at the
Centro Interdipartimentale di Ricerche Agro-Ambientale ‘E. Avanzi’ of the University of Pisa (Lat.
43°40’ N; Long. 10°19’ E). From 1993 till 1998 the experiment consisted in a grain maize (Zea
186
mays L.) continuous crop. In 1998 the experiment has been transformed into a two-year crop
rotation between maize and durum wheat (Triticum durum Desf.), with only one main crop present
each year. Cover crops ((rye (Secale cereale L.), subterranean clover (Trifolium subterraneum L.)
and crimson clover (Trifolium incarnatum L.)) are sown in the autumn after wheat harvest and are
killed with glyphosate in the spring, just before sowing of maize. The experiment has been set up as
a split-split-plot design with two crop management systems (conventional and low-external input)
in the main plots, four nitrogen fertilisation levels (0, 100, 200, 300 kg ha-1 mineral N for maize and
0, 60, 120, 180 kg ha-1 mineral N for wheat) in the sub-plots, and four cover types (stubble of the
previous crop, subterraneum clover, crimson clover and rye) in the sub-sub-plots. The conventional
system consists in ploughing (at ca. 30 cm depth), application of post-emergence herbicides and
underploughing of the cover crops, while the low-external input system is based upon no-tillage,
application of pre-sowing glyphosate + post-emergence herbicides and surface mulching of the
cover crops. Every treatment is replicated four times in sub-sub-plots of 21 x 11 m, with a total of
128 sub-sub-plots. The highest fertilisation level will be excluded from these studies; this means
that a total of 96 sub-sub-plots will be studied.
The four weed species selected for bioassays in glasshouse and in the laboratory are among the
most noxious weeds of maize in the study area and are characterised by different seed size:
Amaranthus retroflexus L. (1 mm), Chenopodium album L. (1 mm), Digitaria sanguinalis L. (1.5
mm) and Echinochloa crus-galli (L.) Beauv. (2 mm). All four species are present in the weed
seedbank of the low-input system (Moonen & Bàrberi, unpublished data).
Mechanism 1:
The aim of this study is to determine the combined effect of four soil cover types (three living
cover crops plus wheat stubble), three fertilisation levels and two crop management systems
(conventional vs. low-external input system) on the weed population emerging in the field during
the winter season.
Weeds will be sampled systematically. Weed presence will be monitored during the cover crop
growing period and just before cover crop destruction. The parameter measured will be adapted to
the field situation. During the first sampling period weeds will still be small and thus individuated
and counted individually. At harvest, the biomass of cover crops and weeds will be collected and
oven dried to constant weight.
Mechanism 2:
The aim of this study is to determine: (1) the weed suppression capacity of cover crop residues
in the maize crop following the winter cover crops, (2) the relative contribution of physical and
allelopathic effects of cover crop residues to the weed suppression capacity of several cover crop
mulches, (3) the influence of different soil nutrient levels, due to previous different mineral nitrogen
fertilisation of the main (cash) crops, on the allelopathic capacity of cover crop residues, (4) the
influence of mineral nitrogen fertilisation applied at emergence time of maize and selected weed
species on emergence and growth inhibition of these species by cover crop residues, (5) the
influence of seed size on the susceptibility of weed and crop species to allelochemical interference
and (6) the relation between allelopathic and chemical property dynamics in the cover crop residues
and in the soil.
(a) Field weed population
The aim of this study is (1) to evaluate differences in size and composition of field weed
populations due to the different effect of crop management system, nitrogen level and type of cover
crop residue and (2) to find out if the differences in field weed populations persist during the whole
maize cycle.
187
The field weed population will be sampled at different moments: before and after postemergence herbicide treatment and at maize harvest. Weeds will be sampled systematically.
Sampling method will be adapted to the field situation. At the first sampling weed density will be
counted. For the second sampling, the Braun-Blanquet method (Braun-Blanquet, 1964) will be
applied to monitor weed abundance. At harvest the biomass of maize and will be collected and
determined as described above. In every sampling period, also the thickness of the cover crop
residue layer will be measured and its percent soil cover will be estimated visually.
(b) Emergence and growth of maize and four weed species in a glasshouse experiment
The aim of the glasshouse experiment is (1) to determine the relative contribution of changes in
soil physical characteristics and allelopathic interactions exerted by cover crop residues on
emergence and growth of maize and four weed species and (2) to establish any possible interaction
between nitrogen fertilisation and the effectiveness of allelopathic substances in suppressing weeds.
Soil for the germination experiment in the glasshouse will be collected near the field
experiment location and sterilised to eliminate the active seedbank. A fixed number of seeds will be
distributed in each tub and the amount of cover crop residue to cover them will be the same for each
tub, to avoid any possible effects related to mulch thickness. Tubs with inert poplar (Populus spp.)
mulch will be used as control to test the physical effect of mulches on weed germination and
successive development (Barnes & Putnam, 1983). Irrigation water will be added on top of the
residue to mimic the rainfall pattern that will actually occur in the field in order to wash nutrients
and allelochemicals out of the residue into the soil.
The cover crops are grown in plots that receive different nitrogen fertilisation treatments during
cash crop growth. This can possibly influence the quantity of allelochemicals and nutrients released
by the cover crop residues. Furthermore, the different fertilisation levels applied to maize are likely
to influence the effectiveness of the allelopathic effect exerted by the cover crop residues on weeds.
In order to determine if such an effect exists, every case will be tested with and without additional
nitrogen fertilisation. The parameters that will be measured are emergence percentage, plant height,
number of unfolded leaves and plant biomass at harvest.
(c) Determination of the content of nitrate and allelochemicals in the soil and in aqueous
extracts of cover residues collected at different times after cover crop destruction and
germination and early growth rate of maize and four weed species incubated with addition of
aqueous residue extracts
The aim of this study is to determine: (1) if the allelochemicals reported to be found in rye and
clovers are actually present in the soil and in the aqueous extracts of the cover crop residues and in
what concentration, (2) if the mulches originating from plots subjected to various N fertilisation
levels during cash crop growth release different nitrogen and allelochemical quantities, (3) if these
differences are reflected in the soil nitrogen level, (4) the dynamics of allelochemical and nitrate
release after cover crop destruction, and (5) if the aqueous extracts of the cover crop residues have
an effect on germination and early growth of maize and four weed species.
For this experiment soil and debris will be collected in the low-external input system based on
no tillage. The plots with wheat residue will be used as control plots with natural vegetation cover,
since these plots have not been touched after wheat harvest in July 2001. Cover residue and soil will
be collected and analysed at two-weekly intervals starting at cover destruction.
Six random soil cores will be taken in each plot, mixed and frozen with dry ice to stop
microbial activity. At the same six points, residue samples will be taken, put in a paper bag and
stored in a dry and dark place.
188
Parameters to be determined in the soil are: temperature, nitrate, total N content, C/N, organic
carbon content, pH, phosphorus, potassium, microbial biomass, soil respiration, water content and
phenolic acid concentration. Parameters to be determined in the residue samples are: C/N, total N
content, dry weight biomass and phenolic acid content. Aqueous extracts will be made of the
residue and soil samples, and of the inert poplar mulch.
Of each residue and soil solution, part will be used for a High Performance Liquid
Chromatography (HPLC) to determine which phenolic acids are present (Barnes & Putnam, 1987;
Barnes et al., 1987; Copaja et al., 1999; Kato-Noguchi, 1999), and another part will be used for
analysis of the chemical properties. For the aqueous residue extracts, the remaining solution will be
used to test its effect on germination and early growth of maize and four weed species. For each
sample, seeds will be placed in a Petri-dish treated with the extracts (Weidenhamer et al., 1987) and
incubated at optimal temperatures for each species. Germination percentage and hypocotyle and
radicle length will be measured. Various concentrations of the residue extract will be tested in order
to establish a dose-response curve (Inderjit & Weston, 2000).
Mechanism 3
The aim of this experiment is to determine if cover crops have an effect on the size and
composition of the weed seedbank and on the weed population emerging in the durum wheat crop
following maize and if this effect depends on crop management system and nitrogen fertilisation
level.
Straight after durum wheat sowing, soil cores will be taken for seedbank analysis, carried out
with the seedling emergence method. This experiment will be set up according to the protocol used
for a similar analysis carried out in the same plots in 2000 (Moonen & Bàrberi, 2002) and data will
be confronted with the results of this previous seedbank analysis.
The weed population developing in durum wheat will be sampled at different moments: before
the post-emergence herbicide treatment, two weeks after the herbicide treatment and at wheat
harvest. The weed parameters to be assessed will vary according to the sampling period, as
described above.
Discussion
Although it is not possible to prove allelopathy in the field, we think that this system approach,
combining field observations with ‘nature-simulating’ glasshouse and laboratory experiments, is
able to give valid indications about the relative importance of the various mechanisms by which
cover crops can influence the weed community in the field and about how cover crops can best be
managed to optimise their weed suppression capacity.
The mechanisms responsible for the differences observed in field weed population between the
four cover types grown under various management systems and fertilisation levels should hopefully
be explained by the results of the experiments performed in the glasshouse and in the laboratory.
Therefore it is important that these experiments will be carried out under conditions as similar as
possible to the field situation. This means that:
1. The species used for the bioassays have to be present in the field (Inderjit & Weston, 2000).
2. The soil samples have to be frozen in the field to stop microbial activity since the
microorganisms are able to use phenolic acids as a carbon source (Blum et al., 2000) and
3.
4.
5.
6.
7.
8.
189
we are interested in the phenolic acid concentration of the soil at the moment the sample
was taken.
Since soil physical and chemical characteristics influence allelopathic interactions, the soil
used for the germination experiment in the glasshouse has to be similar to the soil in the
field and will therefore be collected near the field experiment (Inderjit & Weston, 2000).
Since allelopathic effects are found to be density-dependent (Weidenhamer et al., 1989)
each tub should contain the same seed number. This means that the soil will have to be
sterilised to eliminate the active seedbank.
For the same density-dependent effect, the quantity of mulch collected in the field has to be
distributed equally over the tubs with fixed number of seeds.
Irrigation of the tubs in the glasshouse will happen by simulating the actual rainfall pattern
occurring in the field.
The residue and soil extracts used to determine phenolic acid concentration have to be
aqueous extracts at pH similar to soil pH, to determine phenolic acids that can be released
into the soil under natural circumstances (Inderjit & Weston, 2000).
The cover residue will be extracted as found in the field without further grinding before
extraction, to prevent the likely alteration of nutrient and allelochemicals release patterns.
To distinguish between the allelopathic and physical effects on weeds exerted by the mulch
layer, an inert poplar much control will be added. Poplar mulch was found to have a similar
physical effect as rye residue but no release of allelochemical substances was found (Barnes &
Putnam, 1983).
Since soil chemical characteristics, especially pH, organic matter and nutrient status, have been
found to influence the content of phenolic acids present in the soil and therefore allelopathic
interactions, tests are proposed to determine these soil characteristics at the moment of cover crop
destruction and at four different times after cover crop destruction. Also, residue chemical
characteristics will be determined to try to establish a correlation between residue decomposition
and changes in soil chemical characteristics. This, combined with seed germination in Petri-dishes,
will help to establish whether there exists a correlation between residue decomposition and
allelopathic properties of the residue extracts.
In the bioassays, the allelopathic effect of the cover residues will be tested on five different
species in order to establish to what extent species characteristics like seed size or taxonomic group
(monocot vs. dicot) influence their vulnerability to allelochemicals released from the residues. This
will allow us to predict the long-term effect of cover crop management on the weed community
dynamics, e.g. a possible shift in composition towards increased abundance of more resistant
species.
Even though the soil for the germination test in the glasshouse will be sterilised,
microorganisms that mainly originate from the residue material put on top of the soil and from the
irrigation water will probably infest the tubs. Little is know about the effect of microorganisms on
phenolic acids in the soil but it has been reported that in absence of other carbon sources
microorganisms might attack phenolic acids as a carbon source, reducing the effect of allelopathic
interactions in the soil (Barnes & Putnam, 1986; Blum et al., 2000).
190
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192
Comparison of different mulching methods for weed control in organic green bean and
tomato
L. Radics & E. Székelyné Bognár
Szent István University
Faculty of Horticultural Science
Department of Ecological and Sustainable Production Systems
Hungary, Budapest
Absract
Partly because of environment protection and partly because of ecological farming there is more
and more attention on herbicide free weed control in Hungary. One of the main questions of
ecological vegetable production is weed management and possible answer is mulching, which
besides its weed control role reduces evaporation too.
During our examinations we compared weed control effect and yield increasing effect of 8 different
types of mulch in green bean and tomato. We used weedy, hoed and herbicide treated plots as
control. Years of the experiment were 2000 and 2001, two years with significantly different weather
conditions, so our results from these years are very important from this aspect, because of climate
change effects, which increase the numbers of extremely dry, warm and humid years and we have
to fit our farming habits to these effects.
In extremely arid year 2000 plastic sheet, paper mulch and straw mulch showed the best results in
weed control in tomato. These treatments had the higher yield too, and these were significantly
different from the yield of herbicide treated and hoed control plots. In humid year 2001 plastic
sheet, paper mulch and grass clippings caused the lowest weed cover and we got the highest yield in
paper mulched plots in this year.
In green bean in 2000 also the plastic sheet, paper mulch and straw mulch showed the best results in
weed control, but there were no significant difference from control treatments. At the end of
growing season in 2001 high weed cover was observable in every treatment except paper mulched
and hoed plots. We found no significant difference between green bean yields of different plots in
both of the years
After experiences of the two years under above-mentioned circumstances compost and legume
clipping were unsuitable for mulching. Mowed weeds showed negative results too. In these
treatments high weed cover and low yield were noticeable in both years.
Keywords: weed control, mulch, tomato, green bean
Introduction
As we notice the distribution of precipitation in Hungary we can see that amount of rainfall
decreased significantly compared with the term between 1901 and 1950 and annual average
temperature increased slightly. This phenomenon radically modifies sustainability and
successfulness of farming habits, which were accommodated to climatic conditions through many
years. One possible solution is decreasing evaporation with soil covering, which is also a weed
management method. Partly because of environment protection and partly because of ecological
farming there is more and more attention on herbicide free weed control in Hungary. Mechanical
and physical weed management methods that are widespread in ecological farming have significant
expenses, so we need to examine other methods under local circumstances to save expenses.
We can use living plants, plant residues (straw, compost, mowed grass, processing by-products) and
industry-origin materials (black polyethylene foil, paper, felt, different kinds of textile) as mulch.
193
Each mulching material has different weed control effect. Black foils is one of the most standby
methods for weed control but as its disadvantage we have to mention that we have to remove if it is
a non-degradable foil. Environmentally friendly, degradable mulch is paper. It is pervious and after
turning under at the end of growing season it is biodegradable. In West Europe organic mulch is
prevalent. Grass, leafage, straw and mowed weeds are used for interrow covering. Besides its
shading effect it can provide nutrients to the soil. One of the most former mulches is straw, byproduct of plant production. In an Indian experiment straw mulch increased yield of crop and water
keeping capacity of the soil (Moitra et al, 1996). According to Tu et al. (2001.) mulch is not
serviceable for controlling of perennial weeds, because these plants accumulate much nutrient and
break through the covered surface easily. Otherwise in the case of cirsium (Cirsium arvense) thick
straw mulch decreased the number of flowering plants.
According to Agele et al (1999, 2000) grass clipping mulch improve yield of tomato and water
keeping capacity of the soil according to uncovered control. It increased the amount of water in the
top 5 cm of the soil and decreased soil temperature in the top 5 cm. In the case of late planted
tomato they reached faster growing and higher yield with mulching before drought came.
By using the results of this experiment we will be able to set up a system, which is suitable for weed
control, helps to protect soil structure and water content and encourages soil life. This production
system could mean alternative solution for production under arid circumstances, and could avoid
watering and its disadvantages.
Material and method
Ecological circumstances
Years of the experiment were 2000 and 2001, two years with significantly different weather
conditions, so our results from these years are very important from this aspect, because of climate
change effects, which increase the numbers of extremely dry, warm and humid years and we have
to fit our farming habits to these effects.
Soil type is restrainedly deep chernozem-like sandy soil. Soil forming rock is calcareous sand.
Depth of humic layer is 30-40 cm. Soil is fast warmer, with good water permeability and good air
capacity. The disadvantage of this soil type, it is inclined to quick cooling down and drying out.
Weakly calciferous, faintly alkaline soil.
Green beans were sown in first decade of May. Each treatment were established on 10 m2
parcels, beans were sown by 40*25 cm with 3 seeds per each pit. The test plant was dwarf beans,
the variety was: Cherokee. Tomato was planted in second decade of May. Each treatment were
established on 10 m2 parcels, tomatoes were planted by 70*60 cm. The test variety was: Dual (half
determinate).
All the 11 treatments were carried out in 4 repetitions.
Treatments:
1) weedy control
2) herbicide control:
solved into 4 l water into the all 4 repetitions:
9 ml Olitref (before sowing) and 8 ml Dual 960 EC (after sowing)
in tomato: Dual 960 EC (before planting)
3) hoeing control
4) rye straw mulching with 10 cm depth
5) rye straw mulching + Phylazonit M bacteria fertiliser. Phylazonit were applied and ploughed
under immediately before the straw mulching.
6) black plastic covering (fixed on the edges)
7) paper covering (fixed on the edges)
194
8) grass clippings mulch with 10 cm depth
9) alfalfa clippings mulch with 10 cm depth
10) compost mulching with 5 cm depth
11) mowed weeds. Permanent mowing, clipping were left on the surface
Measurements, monitoring
x weed survey (in each month)
x dry mass of weeds
x Crop weight measuring
All the weed surveys were carried out 2 weeks after the treatments (hoeing, mowing). Test plots
were the whole 10 m2 parcels. Surveys were made in: June, July, August 3rd decade. Weed and
tomato/bean cover percentage were registered. All the data were analysed with statistical tests
(Tukey-test).
Results
Tomato 2000
All the registered data of tomato (similar to bean) were analysed in each month. Weed covering
data can be found on the next figure from each treatments.
It is observable that the weed cover percentage was reduced in most treatment because of the
extremely dry August weather studying the monthly surveys.
Weed reducing effect of straw, plastic cover, paper cover and grass clipping mulch (4, 5, 6,
7, 8) treatments were permanent during the whole season. The total weed cover percentage in
herbicide and hoeing control (2,3) treatments was bellow 20%. There were significant difference
between 2, 3, 4, 5, 6, 7, 8 treatments and mowed weed (11) treatment in June, July; alfalfa clipping
(9) treatment in August and compost mulching (10) treatment during the whole season (SD5%). Test
plants could not utilise the nutrients of compost, because it has dried on soil surface quickly. Weeds
could utilise this nutrient source better, therefore the weed cover percentage has grown in this
treatment.
The weed cover percentage in mowed weeds treatment was almost the same as the weed control
treatment, because the dominant weed species was Portulaca oleracea, which can not be controlled
by permanent mowing.
195
Figure 1. Weed cover in 2000 in tomato
We have analysed data according to life forms too.
T = Therophyta
T1 – plants, which are spearing in fall and
ripening in spring
T2 – plants, which are spearing in fall and
ripening in the beginning of summer
T3 – plants, which are spearing in spring
and ripening in the beginning of summer
T4 – plants, which are spearing in spring
and ripening in the end of summer
G = Geophyta (plants, which are overwintering
on the soil surface or under soil and has slanting
or horizontal underground stem)
G1 - plants, which have stoles near to the soil
surface
G3 - plants, which have stoles in deeper and
many levels of the soil
Weeds of T4-life form were dominant in every treatment. Significant difference was observable in
the case of treatments 9., 10. and 11 (SD5%).
There was no statistically certifiable difference between treatments in the case of G3 and G1
(perennial) weeds.
Species of G3-life form (Cirsium arvense, Convulvulus arvensis) reached their highest covering in
herbicide treated plots in June.
196
Figure 2. Cover of weeds in G3-life form in June 2000.
Measurements of dry mass of weeds showed the same results as weed surveys. Straw, plastic foil
and paper mulch had the best weed suppress effect. We found higher dry mass of weeds under
compost mulch than on untreated weedy control plots in July and in August as well. So we can see
from this that compost made better circumstances for weeds too.
Figure 3. Dry mass of weeds in tomato (2000)
There are significant differences between yields of treatments. Both straw mulches, foil and paper
mulch made statistically homogenous group. In these four treatments we measured significantly
197
higher yield than in treatments 9, 10, 11 and in hoed and herbicide treated control (SD5%). In
treatments 9, 10, 11 high weed cover caused the low yield. Differences between yields of hoed plots
and plots of 4, 5, 6, 7 treatments originated in crop showed its gratitude for mulching in that arid
year.
Figure 4. Yield of tomato in 2000.
Tomato 2001
After extremely dry 2000 year in 2001 there was significant amount of precipitation so we could
test covering materials under different circumstances.
In this year compost mulch gave negative result, this treatment showed high weed cover during the
whole growing season. Treatment 10. differed significantly (SD5%) from 3, 6, 7, 8 treatments during
the whole growing season.
Legume clipping (9) seems to be unsuitable for mulching in this year too. Treatment 9 differed
significantly (SD5%) from 3, 5, 6, 7, 8 treatments in July and August.
In 2001 straw, foil, paper and grass clipping mulches (5, 6, 7, 8) showed the best results. In June
every four and in July foil and grass clipping mulches differed significantly (SD5%) from herbicide
treated plots. Straw (4) and straw with Phylazonit M bacteria fertiliser (5) showed different weed
cover, but this difference was not statistically certifiable. The reason for this could be the higher
cover of tomato in treatment 5. Probably in this humid year bacteria fertiliser could prevail and N
fixing and P mobilising bacteria increased nutriment in the soil. This could increase cover of
tomato.
Weeds of T4-life form were dominant in every treatment, these species gave the differences, which
were observed in the case of total weed cover.
There was no statistically certifiable difference between treatments in the case of G3 and G1
(perennial) weeds.
198
Figure 5. Weed cover in tomato in 2001.
Because of sufficient amount of precipitation and the high weed cover at the end of growing season
there are not as big differences between the yields as in 2000. We have measured the highest yield
in paper mulched plots (7) and the fewest in mowed weeds (11) (SD5%). At SD10% paper mulch was
significantly better also than herbicide treated control.
If we compare this with Fig. 5. the highest weed cover was not in treatment 11 (cover of 9, 10 was
higher) but the lowest yield was observable here. This could have two reasons, on the one hand in
treatment 9, 10 legume clippings started to decompose and gave nutrient for the crop. On the other
hand mowed weeds meant probably high concurrence for the crop.
Figure 6. Dry mass of weeds in tomato (2001)
199
Measurements of dry mass of weeds showed the same results as weed surveys. Weed suppressing
effect of plastic foil, paper and cutted grass was observable in whole year.
Figure 7. Yield of tomato in 2001.
Green bean 2000
In foil covered plots bean emerged one week before the ones in other treatments. Under warm and
arid circumstances of 2001 black foil ensured suitable conditions for seed germination. In the
following humid year this difference disappeared. At the end of the growing season in legume
clipping and in compost covered plots weeds were dominant and this difference was statistically
detectable. Measurements of dry mass of weeds showed too that these two mulching methods were
not suitable for suppressing of weeds under these circumstances.
Mowing of weeds reduced weed cover only a little.
Significant differences (SD5%) were in June between 9, 11 and 2, 3, 5, 6 treatments and in July
between 9, 10 and 2, 3, 4, 6, 7 treatments. There was no statistically certifiable difference between
covered and uncovered plots.
Weeds of T4-life form were dominant in every treatment. There was no statistically certifiable
difference between treatments in the case of G3 and G1 (perennial) weeds.
200
Figure 8. Weed cover in green bean in 2000.
There was no significant difference observable between yields of green bean. We measured the
highest amounts in plastic and paper covered plots. In treatments 9, 10, 11 showed the lowest yields
so in these plots weed cover beyond the critical level which manifested in yields. If we compare
these yields with the yields of tomato, we can conclude that tomato showed better reactions to
covered soil surface.
Figure 9. Yield of green bean in 2000.
201
Green bean 2001
In 2001 at the end of the growing season there was high weed cover in every treatments except
plastic and paper mulched ones. In June weed cover only of treatment 11 differed significantly
(SD5%) from the other treatments. The reason was probably that in this treatment rate of
Amaranthus blitoides weed species was high. This species do not grow high but cover a relative big
area. In July compost was significantly (SD5%) different from paper and plastic.
Straw (4) and straw with Phylazonit M bacteria fertiliser (5) showed different weed cover, but this
difference was not statistically certifiable. The reason for this could be the higher cover of green
bean in treatment 5. Probably in this humid year bacteria fertiliser could prevail and bacteria
increased nutriment in the soil, which could increase cover of tomato.
Figure 10. Weed cover in green bean in 2001.
Figure 11. Cover of weeds in G3-life form in June 2001.
Weeds of T4-life form were dominant in every treatment. There was no statistically certifiable
difference between treatments in the case of G3 and G1 (perennial) weeds.
202
Figure 12. Dry mass of weeds in green bean (2000, 2001)
Weed control effect of plastic and paper was not observable in the yields of green bean. As it is
noticeable in Fig. 13. in humid year 2001 there was no significant difference between yields of the
treatments.
Figure 13. Yields of green bean in 2001.
203
Conclusions
We can take the following conclusions on the basis of the extremely dry 2000 and the humid year
of 2001:
- The best results were found in plastic covering and paper covering treatments even in tomato
and bean tests both dry and humid weather conditions for weed control.
- Tomato yield was found significantly (SD5%) higher in plastic covering and paper covering
treatments than in herbicide and hoeing control treatments in dry weather conditions. These
differences were not observable in humid weather conditions. The advantage of paper covering
comparing to plastic is the paper do not pollute the environment and the maintenance is easier at
the end of growing season, when the paper can be simple ploughed into the soil, because it is a
biodegradable material.
- Straw and straw+Phylazonit treatment could give positive weed control effect in dry weather
conditions (2000.) in tomato and bean tests. We measured the second high yield in tomato in the
straw-mulched parcels after the plastic covering treatments. We could find differences between
straw and straw+Phylazonit bacteria fertiliser treatments in yield and covering of test plants
only in humid weather conditions, but it was not significant.
- Grass clipping can be suitable mulch, because it gave better result on yield and covering of test
plants than alfalfa covering.
- On the basis of this two years we did not find acceptable mulching effect in tomato and bean
tests in case of compost and alfalfa clipping in these circumstances.
- We did not find positive result either in mowed weed parcels. We could measure high weed
cover percentage and reduced yield in these plots in tomato and bean tests as well.
- Measurements of dry mass of weeds showed the same results as weed surveys.
- Comparing the yield of bean we did not find any significant difference among the treatments in
the yield of bean in any year.
We can not make final conclusions from these results, it is needed to establish long term
experiments to eliminate the weather condition effects.
204
Acknowledgements
Research was supported by the Ministry of Agriculture and Rural Development.
Literature
AGELE S, IREMIREN G, OJENIYI S (1999) Effects of plant density and mulching on the
performance of late-season tomato (Lycopersicon esculentum) in southern. Journal of
Agricultural Science 133: 4, 397-402, Nigeria
AGELE S, IREMIREN G, OJENIYI S (2000) Effects of tillage and mulching on the growth,
development and yield of late-season tomato (Lycopersicon esculentum) in the humid south of
Nigeria. Journal of Agricultural Science 134: 1, 55-59 Nigeria
MOITRA R, GHOSH D,C, SARKAR S, (1996) Water use pattern and productivity of rainfed
yellow sarson (Brassica rapa L. var glauca) in relation to tillage and mulching. Soil and Tillage
Research, vol. 38, no. 1, 153-160 (8), Depertment of Soil Sciece and Agricultural Chemistry,
Varnasi, India
SMITH A, E, (1995) Handbook of Weed Management Systems. 557-558. New York, USA
TU, M., HURD, C., & RANDALL J, M, (2001) Weed Control Methods Handbook, The Nature
Conservancy, http://tncweeds.ucdavis.edu, Version: April 2001.
205
No-tillage of arable crops into living mulches in Switzerland
Bernhard Streit, Juerg Hiltbrunner, Lucia Bloch and David Dubois
Swiss Federal Research Station for Agroecology and Agriculture, Reckenholzstrasse 191,
CH-8046 Zurich, Switzerland, E-mail: streit@no-till.ch
Abstract
In the last decade, cropping systems with reduced tillage intensity and, in particular, no-tillage
without any soil disturbance has been introduced in Switzerland to prevent mainly soil erosion but
also leaching of pesticides and plant nutrients to the groundwater. In the same time, the organically
cropped acreage has increased substantially. The success of both, no-tillage and organic farming,
have depended strongly on the efficiency of weed control. In no-tillage, weeds have been controlled
so far by applying herbicides. In consequence, the use of no-tillage techniques on organic farms has
not been possible. On the other hand, tillage is the main tool to control weeds on organic farms. As
the organic production is forecasted to increase, environmental problems related with tillage will
become more and more important. Therefore, the development of cropping systems with no-tillage
as the most extreme form of reduced tillage will help to improve the quality and the productivity of
the soils on organic farms.
Sowing crops into stands of living mulch without disturbing the soil seems to be a promising way to
develop no-till systems where no herbicides are used. Results from a field trial in Switzerland with
directly sown winter wheat (Triticum aestivum L.) into stands of white clover (Trifolium repens L.)
and black medic (Medicago lupulina L.) showed the potential of permanent ground cover to
suppress weeds. However, the concurrence between the living mulch and the crops was very
pronounced, in particular during the formation of side shoots and after flowering of winter wheat.
The legumes used as ground cover were usually grown as forage crops and, therefore, were too
competitive. In order to develop a cropping system with no-tillage on organic farms, a research
project has been initiated. The aim of the study will be to evaluate the impact of different living
mulch plants, most of them not suitable for forage production under the cool and humid conditions
of central Europe, different row spacing, and fertilisation with manure on the development of
directly sown winter wheat.
Water and steam for weed control
206
207
Preliminary studies in the comparison of hot water and hot foam for weed control.
R. M. Collins1, A. Bertram2, J-A. Roche1, & M. E. Scott3 .
1
Department of Agriculture, Northam, Western Australia.
2
University of Applied Sciences, Osnabrueck, Germany.
3
Aqua-Therme Pty Ltd, Perth, Western Australia.
Abstract.
Data is presented of trials undertaken late 2001 in Western Australia of thermocouple temperature
recordings of hot water, hot water plus air (with and without foaming agent) and the resulting kill
of 3-4 leaf canola plants grown in pots to simulate broadleaf weeds. Discussion is presented of
ways of inter-relating the physical and biological information in attempt to explain the differences
in the technology. This research is yet incomplete.
Introduction
Aqua-Therme, a Perth-based thermal weed control contractor and equipment manufacturer, has
developed a hot foam variant of their hot water weed control machine. Trials have taken place in
spring and summer 2001-2 at the Department of Agriculture’s Centre for Cropping Systems at
Northam, WA, and at Aqua-Therme’s headquarters in Perth.
The claimed improved performance is based on the addition of compressed air and a ‘biologicallyfriendly’ foaming agent (accepted by the international organic certifying body, IFOAM). The
realisation of the improvement is through either an increase in area covered for the same quantity
of water, or improved insulation of the ground and weeds, resulting in a longer time for the heat to
act on the weeds, or both.
The trials undertaken were to help understand the processes involved in the improvement, and with
this knowledge we would then possibly be able to suggest further improvements.
Materials and methods.
First experiment, 11th & 13 September, 2001.
Canola plants (variety ‘Rainbow’) were grown in a glasshouse in trays 39 cm long, 28 cm wide and
12 cm deep (all internal dimensions), spaced to give five rows of five plants, spaced 5 cm by 5 cm.
Two seeds were placed at each position, but as germination was patchy, additional plants were not
removed. The soil used was loamy sand, but some trays were filled with a peat-based potting mix
to investigate the effect of soil types. The plants were at the 2-3 leaf growth stage when treated.
The hot water weeder used was a truck-based unit normally used for contract street and pavement
weed control in Perth. Hot water delivery is via an insulted hose to a hand-held wand, with a
suitable nozzle to spread the water in a fan (a Spraying Systems HB1/2-5595150 stainless steel fan
nozzle, with 95o spraying angle, was used). The hand lance was set up on a horizontal bar mounted
on the front of a small tractor to give a vertical downward delivery of hot water. Prior to the
experiment, the tractor was speed calibrated to 0.5, 1.0, 1.5, and 2.0 k/hr, the speeds that from
208
experience had shown as covering the operating range. This set-up was then able to transport the
operating lance over the trays with plants. This was done outside, in largely still air conditions.
A ‘dataTaker DT800’ 12 channel data logger was used with 0.3 mm type ‘K’ thermocouples to
record temperatures. Some runs were tried with 12 thermocouples, which resulted in two or three
records each thermocouple per second.
Runs where plants were treated utilised five
thermocouples, giving seven or eight recordings per thermocouple per second. Each run treated
one tray, there being three runs for each treatment (4 speeds x 2 heat delivery methods x 3
replications).
Treated trays were placed back in the glasshouse for several days before counting plants as dead,
severely damaged but recovering, or largely undamaged.
Second Experiment, 6th, 7th, & 11th December, 2001
The experimental procedure was modified in the second experiment after processing and reviewing
the data of the first experiment.
The canola variety was changed to the more vigorous variety ‘Mystic’, more care was taken with
seed placement (seeding depth, seed covering), watering, and the layout was changed to 3 rows of
3 plants, all 40 mm apart, in smaller, more easily managed pots. Plants were transplanted early to
fill spaces where none had germinated, and surplus plants were cut off, so that every pot had 9
plants. Pots were graded for plant size, and samples of top growth were taken to give green and
dried weight for an assessment of the amounts of plant material heated. Some pots of 3 size ranges
(plants varied in height from 5 to 10 cm, predominantly 6 – 8 cm, 3-4 leaf) were used in each run.
A pot numbering system was used that enabled linkage of ‘run’, direction of travel, and plant size,
for later observations.
Five thermocouples were used for the dynamic tests, and were set up in a row between the first and
second plant in each row (three thermocouples), and in the gap between the rows (two
thermocouples). Five readings were taken from each thermocouple per second. Temperatures
were taken of the nozzle output before each run. The nozzle was mounted 75 mm above the pot
soil level, pointing downward.
A patternator, with collection channels 20 mm apart, was used to collect hot water or foam for
weighing. This was to give a more accurate measure of the heat input and where it went.
Temperatures were taken in each patternator channel, but the temperature data was very variable
and lower than expected. The exposed end fine wire thermocouples reacted too quickly to
temperature variations in and around the hot fluid stream. An alternative encased probe
thermocouple was used for these measurements, giving higher values, nearer to the peaks achieved
from the dynamic tests.
The experiments were done inside a building to reduce any affect from wind (not present in the
first experiment).
Infiltration measurements were taken of the two soils.
Third experiment, February 2002
As this is being written, a third experiment is being set up, with results to be discussed at the
Workshop in March, 2002, at Pisa. Aqua-Therme are finding that their use of compressed air with
hot water is producing results equivalent to that achieved with the addition of the foaming agent, so
209
this third experiment was to further improve technique and get more data. It had been found that in
the second experiment, complete drenching of plants in the outside rows was not occurring. Many
plants were observed to lose lower leaves, with unaffected upper leaves. As a result, plant spacing
was reduced from 4 cm to 3 cm. Only the loamy sand soil was used this time.
Results
Variation across the spray swath
100
90
80
70
C
Hot water
HW + air
Foam
60
50
40
30
TK 1
TK 2
TK 3
TK 4
TK 5
TK 6
TK 7
TK 8
TK 9
TK 10 TK 11 TK 12
Thermocouple reading, 3 cm apart
Figure 1. Temperature across hot water, hot water plus air, and hot foam sprays, with spray nozzle 12.5 cm above
thermocouples (static test).
Percentage fluid weight in each position
30
25
20
Hot Water
Hot Water +Air
15
Hot Foam
10
5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Patternator Position, 2 cm spaces
Figure 2. Relative weight of fluid collected across the spray swath.
14
15
210
Figure 1 illustrates the temperature recordings achieved in the first experiment, where the spray
was directly over thermocouples mounted through 3 cm spaced holes in a piece of wood.
Temperatures reduced away from the centre of the spray ‘swath’, due to the reduced quantity of the
fluids distributed to the outside of the spray swath from the fan nozzle (Fig. 2), and the greater
exposure to the cooling effect of air.
The plant kill achieved reflected the same variation across the swath (Fig. 3)
120
Plant Survival, %
100
80
Water
Foam
60
40
20
0
10
5
0
5
10
Cm from swath centre
Figure 3. Plant survival across spray swath, mean of 0.5, 1.0, 1.5, & 2.0 k/hr data, first trial.
90
80
70
60
50
40
30
20
10
0
TK 1
TK 2
TK 3
13
:5
1:
55
13
:5
1:
55
13
:5
1:
56
13
:5
1:
57
13
:5
1:
58
13
:5
1:
59
13
:5
2:
00
13
:5
2:
00
13
:5
2:
01
13
:5
2:
02
13
:5
2:
03
13
:5
2:
04
C
Temperature and time.
The data logger record can be represented graphically. Runs were done statically (Fig 1.) and at
the four speeds and three fluids, with most records taken 5-10 mm above ground but also with
T im e (h o u r s , m in u te s , s e c o n d s )
TK
TK
TK
TK
TK
TK
TK
TK
TK
4
5
6
7
8
9
10
11
12
Figure 4. Temperature versus time, with 12 thermocouples placed at 3 cm intervals across spray swath (0.5 km/hr).
211
some thermocouples poked into the soil (5-10 mm depth) for some runs. The ‘spaghetti’ effect
from the lines of Fig. 4 can maybe seen more clearly as a surface, as in Fig. 5 (same data).
Run 3 (13/09/01), 0.5 km/hr, water, nozzle 12.5 cm above thermocouples 3 cm
apart
TK 12
TK 11
TK 10
TK 9
TK 8
80-90
TK 7
70-80
60-70
TK 6
TK 5
13:52:04
13:52:04
13:52:03
13:52:03
13:52:03
13:52:02
13:52:02
13:52:01
13:52:01
13:52:00
13:52:00
13:52:00
13:51:59
13:51:59
13:51:58
13:51:58
13:51:57
13:51:57
13:51:57
13:51:56
13:51:56
13:51:55
13:51:55
13:51:55
C
TK 4
50-60
40-50
30-40
TK 3
20-30
10-20
TK 2
0-10
TK 1
Time
Figure 5. ‘Surface’ representation of thermocouple data
Figures 4 and 5 illustrate the first difficulty: effectively measuring temperature. The 0.3 mm
thermocouple wire diameter was chosen as the nearest readily available size to that used by Ascard
(1995), and after experience with a 3 mm diameter wire thermocouple with joint protection that had a
very slow response time. The disadvantage is that even small air movements affect temperature values
and it was difficult to obtain ‘average’ data.
Plant kill data.
90
80
Survival, %
70
60
50
W ater
Foam
40
30
20
10
0
0.5
1
1.5
Speed, km/hr
Figure 6. Average canola plant survival after one treatment.
2
212
80
70
Plant Survival (%)
60
50
Potting Mix 13/12/2001
40
Soil 13/12/2001
Soil 17/12/2001
30
20
10
0
0.5
1
1.5
2
Speed, kph
Figure 7. Plant survival after hot water treatment, 6th December, 2001.
Figures 3 and 6 summarise the results from the first experiment, and Figs. 7 and 8 present the
results of the second trial. The second two graphs show assessments made seven days and 11 days
after treatment, indicating that there may differences caused by different soils and an interaction
with the weed control method. The better kill achieved compared to the first experiment is largely
due to proportionally more of the plants being central to the swath.
90
80
Plant Survival (%)
70
60
50
Soil 13/12/2001
40
Soil 17/12/2001
30
20
10
0
0.5
1
1.5
Speed, kph
Figure 8. Plant survival after hot foam treatment, 6th December, 2001.
Plant weight and size
Table 1. Plant weight, g.
Plant height, cm Wet weight Dry weight
4
0.368
0.042
5
0.457
0.047
6
0.584
0.064
7
0.715
0.081
8
0.838
0.099
9
0.865
0.099
2
213
Soil Infiltration
As a means of qualifying the differences between the soils used, measurements of infiltration and
wet and dry bulk densities were taken. Infiltration was from a 55 mm ring on the pot soil surface,
measured when the soil was at wilting point and at field capacity (pot volume 1400 mL).
Table 2. Soil infiltration rates and bulk densities at field capacity and wilting point moisture contents.
Soil type
Sandy loam
Potting mix
Infiltration, wet
80 mL/min.
460 mL/min
Infiltration, dry
110 mL/min.
20 mL/min
Bulk density, wet
1.565
0.686
Bulk density, dry
1.356
0.432
Discussion
Thermodynamics
In analysing the data from the first trial, the variation in nozzle output and temperature across the
swath has been a major difficulty. Calculations of ‘applied energy per m2 ‘ have shown a poor
transference of combustion heat (3.92L diesel/h) to the water of around 60%, and ‘plant survival’
data from each run is very variable. This variability makes it difficult, if not impossible to
calculate a meaningful dose-response non-linear regression (after Ascard, 1995). The second trial
has helped overcome this, by placing proportionately more plants near the centre of the swath and
by using a patternator to measure the amount of fluid that lands in each strip across the swath, but a
full thermodynamic analysis is incomplete.
When thermocouple maximum temperatures are compared to plant survival, a method suggested
by Ascard (1995) as sometimes giving similar or higher correlations with weed control than the
temperature sum method, the results are dominated by the soil type and the fluid used, with
relatively small changes in the maximum temperature. This was taken as the mean of the highest
temperatures of the five thermocouples used in the second experiment.
Plant Survival, %
H ot W ater P otting m ix
H ot Foam P otting m ix
H ot W ater S oil
H ot Foam S oil
80
70
60
50
40
30
20
10
0
60
65
70
75
80
85
90
M ean M axim um Tem perature, C
Figure 10. Plant survival in relation to maximum temperature.
This data suggests that plant survival is very sensitive to temperature at these low temperatures.
The fluid and soil type both have an effect on the temperature achieved. The foam has the
introduction of 5 cubic feet (0.142 m3 ) of ambient temperature air per minute, and Fig 1 shows the
typical pattern where the hot foam temperature is below that of hot water. The infiltration data
shown in Table 2 illustrates how variable this parameter can be. The foam produced was very
214
‘thin’, more like frothy dishwater than shaving cream, and drained readily, and the fact that AquaTherme now no longer use the foaming agent indicates that it is not very different to hot water plus
air.
Soil Factors
Where water is used as the medium for delivering heat to the weeds, the soil has a part to play. It
has been observed that where water ‘ponds’ before infiltrating or running away on the surface,
there is often a better plant kill. Collins (2000, unpublished data, reproduced in Fig 9) has
thermocouple readings from the field where ponding was an observed factor that helped the hot
water temperature stay higher for longer.
Water+Foam+Air
Water+Air
Water
95
90
Degrees Celsius
85
80
75
70
65
60
0
0.25 0.5 0.75
1
1.25 1.5 1.75
2
2.25 2.5 2.75
3
3.25 3.5 3.75
4
4.25 4.5 4.75
5
5.25 5.5 5.75
6
Time, minutes
Figure 9.Temperature decline at soil surface after heat application.
The sandy loam soil generally had a lower infiltration rate than the potting mix, although the latter
had a distinct ‘non-wetting’ characteristic when dry. Although no soil moisture measurement was
taken at the time of treatment, the potting mix was reasonable moist when treated, and no water
was seen to pond. Water did pond with the loamy sand soil.
Plant kill
It was realised since the first two experiments that the outer rows of plants may not have been
completely doused by the hot fluid. Re-examination of photographs taken, show plants where the
lower leaves have been blanched but upper leaves were unaffected. The third trial was to reduce
this affect.
Another observation was a thickening of the stem at ground level of some of these outer row
plants, perhaps suggesting that ‘ring-barking’ may be a factor. This would be where hot water or
foam on the surface might kill the outer phloem tissue of the stem (stopping carbohydrate
movement downward, so producing the thickening), but the inner xylem tissue that transmits water
still be alive. Some speculative observations were made that some plants, if truly ring-barked,
might die. Far fewer did than estimated from the ground level stem swelling, so presumably the
damage was not as serious as it appeared.
215
Conclusions
Experimental method has been inadequate to show why Aqua-Therme is finding that air added to
hot water gives greater economy in weed control over hot water alone. The research is continuing,
with modifications to experimental procedure in order to find a way to clearly demonstrate the
difference. In the process, the effect of soil type and its moisture content has been identified as
having some bearing on the results. These forms of thermal weed control are operating at
relatively low temperature levels and a difference of a few degrees in temperature achieved is often
all
there
is
between
good
and
poor
results.
There is still considerable interest in thermal weed control in Australia and New Zealand, with
several companies currently working on improved water-based (including steam) models.
Acknowledgments
David Bowran, Grain Production Manager, Department of Agriculture, Western Australia, for his
continued support of alternative weed control research in the Western Australian wheatbelt;
The Grains Research and Development Corporation of Australia for funding of the principal author
to the EWRS 5th Physical and Cultural Weed Control Workshop, Pisa, 11-13th March, 2001.
References
ASCARD J (1995) Thermal weed control by flaming: biological and technical aspects. PhD
dissertation, Swedish University of Agricultural Sciences, Alnarp, Sweden. ISSN 0283-0086
216
Band-steaming for intra-row weed control
B. Melander, T. Heisel & M. H. Jørgensen*
Danish Institute of Agricultural Sciences, Department of Crop Protection,
Research Centre Flakkebjerg, DK-4200 Slagelse, Denmark, Bo.Melander@agrsci.dk
*
Danish Institute of Agricultural Sciences, Department of Agricultural Engineering,
Research Centre Bygholm, DK-8700 Horsens, Denmark
Abstract
Steaming the soil prior to crop sowing has the potential of eliminating weed seedling emergence
completely. Thus, steaming might be a perspective technique for intra-row weed control in nonherbicidal row crops of high value, where manual weeding can be very laborious. This paper
presents some preliminary results with the effects of steaming on weed seedling emergence. The
work is part of a joint project involving both biological and technical aspects of steaming. The
overall objective is to develop an applicable technique for applying steam in bands corresponding to
the intra-row area of a row crop. Band-steaming is expected to use much less energy as compared to
current steaming techniques for arable usage.
Introduction
Steaming the soil prior to crop sowing has demonstrated the potential to kill all viable weed
seeds in the heated soil volume. Former investigations with steaming the soil have shown that a
very effective and prolonged weed control can be obtained. Weed species, such as Senecio vulgaris,
Stellaria media and Poa annua, can be controlled almost completely, and the effect may persist for
several months. To achieve that, the temperature must be raised to more than 70oC down to 2,5 cm
soil depth, and this temperature must be maintained for 6-9 minutes (Bødker & Noyé, 1994). The
lethal effect of heating on weed seeds is also known from composting and mulching. Most viable
weed seeds loose their germination capacity when temperatures reach approx. 60oC under mulches
and in composts and persist for a longer duration (Davies et al., 1993; Grundy et al., 1998).
Thus, soil steaming appears to be a perspective method for eliminating hand-weeding in nonherbicidal row cropping, particularly in slow germinating and developing vegetable crops, such as
direct-sown onion, leek and carrots, where manual weeding can be very laborious (Melander &
Rasmussen, 2001). Current steaming techniques for field use are extremely energy consuming,
which in the present work has lead to the idea of applying steam in bands only, corresponding to the
intra-row area of a row crop. Thereby a lot of energy can be saved as compared to steaming the
entire surface and down to 10-15 cm soil depth. However, more technical and biological research is
needed to develop a band-steaming technique that can be applicable for practical usage. This
presentation contains some preliminary biological results from a joint project involving both
technical and biological aspects of band-steaming. The results are from studies aiming at describing
the relationship between weed seedling emergence and maximum soil temperature achieved by
steaming the soil at a range of times. The relationship is essential for determining the amount of
steaming necessary to eliminate weed seedling emergence effectively.
217
Two investigations were conducted in the laboratory, where soil steaming took place in a 7 x 8
cm circular groove made in a wooden wheel with insulation in the bottom and at the sides (Fig. 1).
Soil was steamed by a timed flow of steam through rubber tubes, each connected to a tine with two
1.5 mm holes. Four steam generators with a total effect of 8 kW produced steam. A total of eight
tines were placed so that the soil volume in the groove was steamed evenly. The soil temperature
was continuously measured by eighth thermocouples placed evenly in the soil while steaming and
in a short period after steaming had been stooped. The soil was collected from a sandy loam
expected to contain many natural weed seeds of different species. Samples were collected in
October 2000 for the first experiment and March 2001 for the second one. In the second
experiment, seeds of oil seed rape (Brassica napus) and ryegrass (Lolium perenne) were added to
the samples prior to steaming. Steaming took place a few days after soil samples had been collected
from the field. After steaming, half of the soil fractions were chilled at 5ºC for 30 days in order to
break seed dormancy. Both chilled and non-chilled soil fractions were germinated for 6 weeks in
watered trays in the glass house, and weed seedling emergence was registered regularly on species
level in the germination period. Each treatment was replicated three times.
Figure 1. A circular groove for band-steaming in the laboratory
Steaming time was slightly curvilinearly related to the achieved maximum temperature in the
soil samples (Fig. 2a). For example, it took approximately 90 sec. to reach a maximum soil
temperature of 75oC, and the temperature only dropped slowly, approximately 1oC per 60 sec., after
steaming had been stopped.
The relationship between weed seedling emergence and maximum soil temperature was
adequately described by an S-shaped dose-response curve for both the chilled and non-chilled seeds
Fig. 2b). The curve in Fig. 2b was fitted to the total number of emerged seedlings (weeds plus rape
and ryegrass) from the soil collected in the spring 2001, but data from the autumn 2000 sampling
showed the same relationship. Individual weed species including the crop seeds all showed this Sshaped relationship, but the maximum temperature at which no seedlings emerged any longer was
100
200kW
a)
8kW
80
60
40
20
0
218
Seedlings (no. per tray)
Max. soil temperature (oC)
b)
60
no chilling
50
chilling
40
30
20
10
0
0
20 40
60 80 100 120
Steaming time (sec.)
0
20
40
60
80
100
o
Max. soil temperature ( C)
Figure 2. a): measured (x) and modelled (—) relationship between achieved maximum soil
temperature and steaming time with 8 kW effect and the same theoretical relationship
with 200 kW effect (---). b): relationships between number of emerged seedlings (weed
plus crop seeds) and maximum soil temperature with (---) or without (—) chilling.
different: Capsella bursa-pastoris 70oC; Chenopodium album 65oC; Tripleurospermum inodorum,
Polygonum spp. and grass weeds 60oC; ryegrass and rape 75oC. Chilling generally lowered seedling
emergence of all the weed and crop species in the untreated trays and in those where the maximum
temperature did not exceed 40 oC, probably because chilling caused non-dormant seeds to become
dormant. However, the opposite was true for Polygonum spp. in the soil collected in the autumn
2000, where chilling had broken dormancy of the majority of the seeds, and thus more seedlings
emerged in the chilled fractions. The lethal effect of steaming on dormant Polygonum spp. seeds
was, however, similar to that found for the non-dormant weed species.
Figure 3. A prototype band-steamer with a 200kW steam generator. Thirteen steaming tines are
placed along a 7-cm wide line on the towed frame that is mounted to the 3-point linkage
of the tractor.
219
The determination of the relationship between weed seedling emergence and maximum soil
temperature constitutes a valuable fundamental model for further studies on the effects of steaming.
The next experiments will focus on the lower part of the curve, where weed seedling emergence is
reduced by more than 70%. It is planned to investigate the influence of factors, such as soil type,
soil moisture content, texture of the seedbed (fine versus coarse), and characteristics of the weed
seeds in terms of thickness and hardness of the seed coat. In the technical part of the project, it is
planned to develop a prototype band-steamer for field use, and the first version has already been
build (Fig. 3). A band-steamer would have to work at a reasonable driving speed to become relevant
for practical use, otherwise the working capacity would be to low. Increasing the effect of the steam
generator will affect strongly the time required to achieve a certain maximum temperature as
illustrated in Fig. 2a for a 200kW steam generator under ideal conditions. Another aspect of interest
is the perspective of sowing crop seeds in the heated soil shortly after steaming, so that steaming
and sowing can be done in the same pass. The current prototype uses a 200kW-steam generator, and
it is planned to rear-mount sowing equipment.
References
BØDKER L. & NOYÉ G. (1994). Effekten af varmebehandling af overfladejord i nåletræssåbede
over for ukrudt og rodpatogene svampe. (Effect of heat treatment of surface-soil in raised
seedbeds with conifers against weeds and root pathogens. With English summary). In:
Proceedings 11th Danish Plant Protection Conference / Pests and Diseases, 239-248.
DAVIES D.H.K., STOCKDALE E.A., REES R.M., MCCREATH M., DRYSDALE A.,
MCKINLAY R.G. & DENT B. (1993). The use of black polyethylene as a pre-planting mulch
in vegetables: Its effect on weeds, crop and soil. Proceedings of the Brighton Crop Protection
Conference – Weeds, 467-472
GRUNDY A.C., GREEN J.M., & LENNARTSSON M. (1998). The effect of temperature on the
viability of weed seeds in compost. Compost Science and Utilization, 6(3), 26-33
MELANDER B. & RASMUSSEN G. (2001). Effects of cultural methods and physical weed control
on intrarow weed numbers, manual weeding and marketable yield in direct-sown leek and bulb
onion. Weed Research 41, 491-508.
220
Development of innovative machines for soil disinfection
by means of steam and substances in exothermic reaction
1
A. Peruzzi1, M. Raffaelli1, M. Ginanni2, M. Mainardi2
D.A.G.A.E., Settore Meccanica Agraria, University of Pisa, Italy; 2Centro Interdipartimentale di
Ricerche Agro-Ambientali "E. Avanzi", S. Piero a Grado, Pisa, Italy
Abstract
Several prototypes of a machine (drawn, mounted and self-propelled) for soil disinfection by
means of steam injection at different depth after the incorporation in the soil of varying amounts of
compounds (KOH, CaO, etc.) that cause an exothermic reaction were developed by the Celli firm in
co-operation with the researchers of the Settore Meccanica Agraria e Meccanizzazione Agricola of
the DAGA of the University of Pisa.
In the three years period 1998-2001, research was carried out taking into account the
mechanical, operative, economical, agronomic and phytopathological aspects of soil disinfection
performed with the prototypes. Working times of the machine were rather long and fuel
consumption rather high. Nevertheless, its performances and operating costs are wholly acceptable
taking into account that any interventions of soil disinfection are usually very costly.
The tested system showed a promising potential as it was able to perform a remarkable soil
heating and to control soil pathogens and potential weed flora.
The experiments carried out at the Centro Interdipartimentale di Ricerche Agro-Ambientali “E.
Avanzi” of the University of Pisa, during 1999-2001 obtained very promising and encouraging
results, highlighting among other things the ever greater need to optimize the system through the
development and maintenance of efficient machinery, better understanding of action mechanisms
and a rigorous definition of operational factors (tillage depth, advancement speed, type and dosage
for substance in exothermic reaction) in relation to various substrates, plant diseases and crops.
Introduction
One of the gravest phytopathological problems connected with the cultivation of specialized
horto-floricultural crops, whether in the open field or greenhouse, are “diseases” provoked by
telluric pathogens that must almost always be removed from the soil by disinfection. This is
accomplished in most cases through the application of methyl bromide usually giving very positive
phytoiatric and productive results (Martino, 1997). Environmental, hygienic-sanitary and
toxicological considerations constrain the inclusion of this disinfectant in the Montreal Protocol
which totally prohibits its use from 2005 on (Ferrari et al., 1998; Gullino, 1998; Gullino et al.,
1999; Katan, 1999). The disappearance within a few years of the only active principle able to
guarantee good phytoiatric results under all conditions makes it particularly urgent to develop new
defense strategies. In this respect, an “alternative” method that has shown promise of significant
results is “solarization”. Though it is ever more widely diffuse in use, it is apparently penalized
however because it is strongly dependent on climatic and seasonal factors and the need for a long
interruption in the cultivation cycle (Katan, 1987; Katan et al., 1976; Materazzi et al., 1987; Triolo
et al., 1991).
The only alternative system to both chemical disinfectants application and soil solarization is
represented by steaming the soil. This technique is well known and was widely used in the past, but
the high cost of production and distribution of steam in comparison with methyl bromide
application reduced relevantly its use (Nederpel, 1979).
221
Taking into account these problems, a new system for soil disinfection (called Alce-Garden) by
means of specific operative machines was developed by the Celli firm in co-operation with the
researchers of the Settore Meccanica Agraria e Meccanizzazione Agricola of the DAGA of the
University of Pisa (Peruzzi et al., 2000).
The “Alce-Garden” system
A valid alternative to disinfection by methyl bromide and employment of environmental
friendly methods but too labor intensive for horto-floricultural crops growers, might be the adoption
of a system that employs drawn, or self-propelled operative machines capable of disinfecting soil
using steam aimed at optimizing efficiency, reducing energy consumption and expenditure. It
proposes an interesting innovation involving the deployment and incorporation into the soil of a
substance that has low environmental impact and is compatible with successive cultivation, is
capable of reacting exothermically with steam (for example KOH and CaO) and releasing an
additional quantity of thermal energy for heating the soil.
The exothermic reaction can have various positive effects towards effective soil disinfection in
that it can aid in producing a greater rise in temperature, prolong the realized temperature rise and
produce a direct effect on parasites and weed seeds. The substances to be employed have been
identified on the basis of their low impact on the environment, along with an assessment of the
possible advantages associated with their incorporation in the soil (pH correction, contribution of
nourishing elements, etc.). Adoption of “Alce-Garden” method would therefore permit crop
planting in the soil immediately after treatment (Peruzzi et al., 2000). This method should be carried
out in a single pass by combined modular equipment as shown in figure 1.
a
c
b
Fig. 1. Scheme of the disinfection treatments performed by means of Alce-Garden system: (a)
substance distribution; (b) incorporation in the soil by means of a rotary hoe; (c) steam
injection.
Some experiments were carried out in this respect at the Centro Interdipartimentale di Ricerche
Agro-Ambientali “E. Avanzi” of the University of Pisa during the three years period 1999-2001.
The machines for soil disinfection
The machines for soil disinfection have been closely improved in the testing period. However,
the Alce-Garden system was always performed by means of the distribution of different amounts of
substance in exothermic reaction, its incorporation in the soil (using a blade rotor powered by an
222
hydraulic engine) and the pass of a holed bar that injects steam at a adjusted depth, followed by a
ridging-mulching machine able to ridge - and eventually cover with plastic film - the treated soil.
The scheme shown in figure 2 represents the last and innovative system realized and set up to
perform the disinfection of the soil according to the Alce-Garden method.
The operative machines for soil disinfection realised and set up in the testing period are both
drawn/mounted (thus coupled to a tractor) and self-propelled (4WD and track versions).
2
4
10
3
1
10
9
8
6
5
7
3
Fig. 2. Scheme of the improved system to perform soil disinfection treatments: (1) frame; (2)
hopper of the exothermic reaction product; (3) mechanic drive to the dispenser; (4)
exothermic reaction product; (5) incorporation in the soil by means of a blade rotor; (6)
hydraulic engine; (7) steam injection; (8) roller; (9) ridging-mulching machine; (10)
adjustment of working depth.
The drawn and the mounted implements (Fig. 3) were projected and realised to perform open
ground treatments, while the self-propelled machines (particularly the track version) (Fig. 4) were
projected and realised to work in greenhouse and tunnel (but obviously they can be used also in
open ground).
3
1
2
6
8
4
5
7
Fig. 3. Scheme of the mounted machine for soil disinfection able to perform open ground
treatments: (1) water tank (2) steam boiler; (3) hopper of the exothermic reaction product;
(4) blade rotor; (5) steam dispenser; (6) plastic mulch spool; (7) roller; (8) ridgingmulching machine.
223
All the implements are equipped with a water tank, a steam boiler, a hopper for the substances
in exothermic reaction equipped with an appropriate system for their distribution, a blade rotor
(operating at a speed of 70-80 rpm) powered by an hydraulic engine, a steam dispenser bar and a
ridging-mulching machine.
1
2
6
4
8
4
3
5
7
Fig. 4. Scheme of the self-propelled machine for soil disinfection able to perform greenhouse
treatments: (1) machine with steam boiler, control board and generator; (2) hopper of the
exothermic reaction product; (3) blade rotor; (4) system for the adjustment of rotor working
depth; (5) steam dispenser; (6) plastic mulch spool; (7) roller (8) ridging-mulching
machine.
The main characteristics of the last version of drawn and track self-propelled machines for
soil disinfection are shown in Table 1.
The amount of substances in exothermic reaction (KOH or CaO) can easily be changed (from a
minimum of 50 kg ha-1 up to a maximum of 15.000 kg ha-1) by means of a system that allows to
adjust the surface of the holes placed on the bottom of the hopper. The function of the blade rotor is
only to incorporate the substance in the soil layer that must be treated. Thus the soil must be already
tilled and seedbed must be already properly prepared because the machines performed soil
disinfection and not soil tillage.
224
Table 1. Main characteristics of the last versions of machines for soil disinfection.
Characteristics
Machines for soil disinfection
Track self-propelled
Drawn
Length
(m)
3.80
4.70
Width
(m)
1.60
2.00
Height
(m)
1.50
2.50
Mass
(kg)
3000
3000
Working width
(m)
1.60
2.00
3
0.23
0.31
Hopper capacity
(m )
Tanks capacity
(m3)
0.60
1.60
Steam boiler
0.60
1.30
(kg h-1)
• Flow
-1
(MJ
h
)
1507
3265
• Power
(kg h-1)
42
90
• Max. fuel consumption
(MPa)
1.15
1.15
• Pressure
Engine
(kW)
44
• Power
-1
(kg h )
11
• Max. fuel consumption
Transmission
Hydrostatic
Speed range
(m h-1)
60 - 2500
The water contained in the tanks must be of “good quality”. However, a specific farm cart with
a softener operated by an electric engine powered by tractor PTO was built to improve water quality
in the field.
Evaluation of soil heating
Test methodology
Machine effectiveness was assessed in terms of efficiency in heat transfer and persistence in the
soil. PT100 sensors 4 cm long that send a voltage signal to data loggers from which data are
acquired and recorded on a personal computer using specially designed software were set at
different depths and used for these trials. These surveys were carried out on plastic “chests” (with
parallelepiped shape, square base with side of 30 cm and height equal to 50 cm) and in the open
field at different depths.
Different treatments (carried out at different driving speed with steam + different amounts of
the two exothermic substances and only steam on covered with plastic mulch and not covered soil)
were compared during the three years of tests, using different experimental designs. However, only
the effect of machine speed and the main effects of a single dose of the two exothermic substances
(4000 kg/ha of KOH and CaO) and of soil covering are presented in this paper.
The temperatures were measured for six hours and after divided in four “classes” (T<40°C;
40 T<60°C; 60 T<80°C; T 80°C). The time of persistence in the soil of each class and the
highest and the final (after six hours) values of temperature were taken into account in order to
compare the effects of the different treatments.
The influence of machines driving speed on soil heating (in the soil treated with steam + 4000
kg ha-1 of KOH) is shown in figure 5. The temperature decreased as the speed increased and for
speeds higher than 1 km h-1 there was not any appreciable heating of the soil. There is an easy
explanation of this trend. As a matter of fact, steam flow is constant and if speed increases the soil
is treated with lower and lower amounts of steam. This result was achieved during the first
225
experimental tests. Consequently the following tests were carried out using only one very low
driving speed (150 m h-1), able to allow a remarkable heating of soil according to the need of
performing soil disinfection.
100
90
80
70
60
50
40
30
20
0
20
40
60
80
100
120
Time (min)
150 m/h
300 m/h
500 m/h
Control
Fig. 5. Trend of the temperatures registered in a soil layer of 20 cm treated with the machine for soil
disinfection with three different speeds with a dose of 4000 kg ha-1 of KOH and untreated
(control).
The effect of the use of the two exothermic substances on soil heating (0-15 cm layer) is shown
in Table 2 (time of persistence of the four different classes of temperature in the soil) and Table 3
(highest and final values of temperature).
The use of steam + 4000 kg ha-1 of KOH and CaO allowed to obtain a higher and longer
heating of the treated soil in comparison with the adoption of steam. The differences between the
effect determined by the two exothermic substances, do not seem to be so relevant, although CaO
allowed to reach a highest value of temperature and to maintain soil temperature over 80°C for a
longer time with respect to KOH.
Table 2. Time of persistence of the four different classes of temperature measured for six hours in
the soil (0-15 cm layer) treated with steam and steam + 4000 kg ha-1 of CaO and KOH.
Different letters mean significant differences for P 0.05 (Duncan test). The values must be
compared only on the rows.
Temperature (°C)
Time of persistence in the soil (mins)
Steam
KOH 4000
CaO 4000
T<40°
104 a
63 b
59 b
40° T<60°
147 b
167 a
163 a
60° T<80°
71 b
78 a
78 a
T 80°
38 c
52 b
60 a
226
Table 3. Highest and final values of temperature measured in six hours in the soil (0-15 cm layer)
treated with steam and steam + 4000 kg ha-1 of CaO and KOH. Different letters mean
significant differences for P 0.05 (Duncan test). The values must be compared only on the
rows.
Values
Temperature (°C)
Steam
KOH 4000
CaO 4000
Highest T
92 c
96 b
99 a
Final T
34 b
37 a
37 a
The effect of the use of plastic mulch on soil heating (0-15 cm layer) is shown in Table 4 (time
of persistence of the four different classes of temperature in the soil) and Table 5 (highest and final
values of temperature).
Table 4. Time of persistence of the four different classes of temperature measured for six hours in
the soil (0-15 cm layer) covered and not covered with plastic mulch. Different letters mean
significant differences for P 0.05 (Duncan test). The values must be compared only on the
rows.
Temperature (°C)
Time of persistence in the soil (min)
Covered with mulch
Not covered with mulch
T<40°
40 b
98 a
40° T<60°
179 a
146 b
60° T<80°
84 a
69 b
T 80°
57 a
47 b
Table 5. Highest and final values of temperature measured in six hours in the soil (0-15 cm layer)
covered and not covered with plastic mulch. Different letters mean significant differences
for P 0.05 (Duncan test). The values must be compared only on the rows.
Values
Temperature (°C)
Covered with mulch
Not covered with mulch
Highest T
96 a
96 a
Final T
38 a
34 b
The effect of plastic mulching on soil heating was relevant, although the highest value of
temperature was not significantly different with respect to that obtained without covering.
Mechanical, and operational aspects of the machines
Test methodology
The mechanical fitness of the different typologies of machines for soil disinfection was
assessed and the principal operational characteristics were determined by means of open-field trials.
The machines were always tested on tilled land and hence already predisposed for sowing or
transplanting. It was planned to operate the machinery on sandy well-watered soils (90% sand, 5%
227
silt, 5% clay) that are typically intended for vegetable crops and to employ two exothermic
substances: “potassium hydroxide” and powdery calcium oxide.
The mechanical trials were carried out in order to determine the correct operation of the various
parts of the machinery under varied working conditions and allowed to document all problems,
proposed solutions and improving modifications to be incorporated.
Operational characteristics inherent to the work environment were also assessed during all field
trials by means of the determination of work times (effective, accessory and operational), fuel
consumption (hourly and unitary, in reference to both the machine and the boiler for producing
steam), operating capacity, power consumption, etc. The data gathered from the trials were then
processed by a specific software developed at the Settore Meccanica Agraria e Meccanizzazione
Agricola del Dipartimento di Agronomia e Gestione dell’Agro-Ecosistema of the University of Pisa
and standardized to an idealized one-hectare field (Di Ciolo & Peruzzi, 1988).
An analysis of the running costs of the machines and the treatments of soil disinfection was
also performed. The standard methodology for the calculation of machinery running cost was used,
considering for the implements a useful life of 10 years and an annual use of 1500 hours year-1
(Cera, 1976; Ribaudo, 1996; Sartori, 1998). Two doses (1000 and 4000 kg/ha) of KOH and CaO
(corresponding to those used in the biological experiments) were taken into account in order to
calculate the costs of the treatment.
The operational performances of the machines for soil disinfection are shown in Table 6. Both
the implements always worked at the same driving speed of 0.15 km h-1. According to the different
working width and water tank capacity, the drawn machine was characterized by a lower working
time (-22%) and a higher work productivity (+28%) with respect to the self-propelled machine. The
total fuel consumption per hectare was on the contrary higher (+63%) for the drawn implement in
comparison with the self-propelled machine, according to the higher power (and consumption) of
both the steam boiler and the 100 kW 4WD tractor coupled to the drawn machine.
Table 6. Operational performances of the two machines for soil disinfection.
OPERATIONAL CHARACTERISTICS
Unit of
measure
machine
Driving speed
150
m h-1
Working depth
m
0.2
Working width
m
1.6
Effective time
41.6
h ha-1
Accessory time
10.9
h ha-1
Operative time
52.5
h ha-1
Work chain efficiency
%
79
Working productivity
2
-1
190
m h
Machine/tractor fuel consumption
450
kg ha-1
Steam boiler fuel consumption
1838
kg ha-1
Total fuel consumption
2288
kg ha-1
Drawn machine
150
0.2
2.0
33.4
7.8
41.2
81
243
576
3146
3722
An analysis of the running costs of the machines and the disinfection treatments performed
with different doses of the two exothermic substances is finally shown in Table 7.
228
Table 7. Analysis of the costs of the two machines and the treatment of soil disinfection performed
with different doses of KOH and CaO.
COSTS
Unit of
Drawn machine
measure
machine
Purchase price
€
123967
72314
Useful life
years
10
10
Annual use
h
1500
1500
Cost per hour
70
81*
€ h-1
Cost per hectare
3661
3347*
€ ha-1
Cost of the disinfection treatments:
4177
3863
Steam + 1000 kg ha-1 of KOH
€ ha-1
3919
3605
Steam + 1000 kg ha-1 of CaO
€ ha-1
5725
5411
Steam + 4000 kg ha-1 of KOH
€ ha-1
4693
4379
Steam + 4000 kg ha-1 of CaO
€ ha-1
* including the cost of the 100 kW 4WD tractor coupled to the drawn machine.
These values must be considered only indicative because the purchase price of both machines
and exothermic substances might be changed in the next future. The running costs of the two
machines are not so different, although the drawn implement is characterized by a higher value of
cost per hour (+16%) and a lower value of cost per hectare (-9%) with respect to the self-propelled
machine. The cost of the treatments is closely influenced by the type and amount of exothermic
substance. However, the average cost of this treatment (calculated averaging the values obtained for
the different machines, substances and doses) is about 4472 € ha-1 and it is of the same order (even
lower of some 4%) of the cost of a chemical treatment performed with methyl bromide (4650 € ha-1
on average).
Conclusions
The Alce-Garden System showed remarkable potential: it successfully induced substantial soil
heating, thereby controlling the development of animal and cryptogamic pathogens as well as weed
seed germination.
Machine working time and fuel consumption were elevated in absolute terms, but were
considered acceptable given that effective soil disinfection was achieved. Moreover, the cost per
hectare of the steam treatment was competitive when compared to methyl-bromide fumigation.
Results obtained in control of plant diseases were highly encouraging. The machine was tested
on heavily nematode-infested soil, where it succeeded in substantially lowering the number of
nematodes and improving the root development of courgettes planted soon after treatment. In
addition, interesting positive results in control of lettuce rot (Sclerotinia minor) were obtained
during the three year-period. The disease was successfully contained by Alce-Garden system, and
favourable effects on lettuce yields and weed control were also observed.
Results of post-treatment soil analysis were likewise good, confirming rapid return to pretreatment soil fertility and microbial activity. Moreover, treatment was not followed by
unfavourable conditions for crop growing, indicating that normal sowing and planting can be
resumed immediately after disinfection with no risk of crop failure. A further positive aspect was
the trend towards higher “activity” observed in soil treated with the Alce-Garden system, in contrast
to the total “sterilisation” resulting from methyl-bromide. This suggests that the proposed system
can offer significant long-run agronomic and environmental advantages.
229
In conclusion, the tests showed that the soil steam machinery manufactured by Celli can
guarantee very good results in terms of “biological” control of soil infested by various pathogens;
moreover both working capacity and costs are fully acceptable. However, there is also a clear need
to conduct further experimental research in order to optimise the system through a better
understanding of its mechanisms of action and a rigorous definition of the operative parameters in
relation to different soil typologies, plant diseases and crops.
Acknowledgements
The authors are very grateful to A. Celli and A. Magni (Celli firm), R. Del Sarto, A.
Pannocchia, M. Paracone, L. Pulga and S. Toniolo (University of Pisa) for their precious help and
co-operation.
References
CERA M (1976) Meccanizzazione Agricola. Ed. Patron, Padova.
DI CIOLO S & PERUZZI A (1988) Proposal for data processing standardization for tillage field
test. Agricoltura Mediterranea 3, 231-236.
FERRARI M, MARCON E & MENTA A (1998) Fitopatologia, Entomologia Agraria e Biologia
Applicata, 3rd edn., Edagricole, Bologna.
GULLINO M (1998) Anno 2005: addio al bromuro di metile. Terra e Vita 7, 22-23.
GULLINO M, MINUTO A & GASPARRINI G (1999) Bromuro di metile - la parola agli
agricoltori. Colture Protette 7, 39-42.
KATAN J (1987) Soil solarization. In:. Innovative approaches to plant disease control, I Chet ed.,
John Wiley & Sons, New York.
KATAN J (1999) The methyl bromide issue: problems and potential solution. Journal of Plant
Pathology 81, 153-159.
KATAN J, GREENBERGER A, ALON H & GRINSTEIN A (1976) Solar heating by polyethylene
mulching for the control of disease caused by soil-borne pathogen. Phytopathology 66, 683688.
MARTINO B (1997) Il bromuro di metile in agricoltura. La Difesa delle Piante 20, 111-116.
MATERAZZI A, IANDOLO R, TRIOLO E & VANNACCI G (1987) La solarizzazione del
terreno. Un mezzo di lotta contro il “marciume del colletto” della lattuga. L’Informatore
Agrario 43, 97-99.
PERUZZI A, RAFFAELLI M, DI CIOLO S, MAZZONCINI M, GINANNI M, MAINARDI M,
RISALITI R, TRIOLO E, STRINGARI S & CELLI A (2000) Messa punto di un prototipo di
sterilizzatore del terreno per mezzo di vapore e di sostanze a reazione esotermica. Rivista di
Ingegneria Agraria 31, 226-242.
NEDERPEL L (1979) Soil sterilization and pasteurization In: Soil disinfestation, D Mulder ed.,
Elsevier Scientific Publishing Company, Amsterdam.
RIBAUDO F (1996) Costo di esercizio delle macchine agricole. Macchine & Motori Agricoli 3, IXI.
SARTORI L (1998) Capitolo V: calcolo del costo di esercizio delle macchine. In: Dispense di
Meccanizzazione Agricola, Ed. Università degli Studi di Padova.
TRIOLO E, MATERAZZI A & VANNACCI G (1991) Risulati di un decennio di ricerche in Italia.
La solarizzazione: un terzo metodo di sterilizzazione parziale del terreno. Terra e Sole 46, 2228.
230
Soil steaming with an innovative machine – effects on the weed seedbank
A.C. Moonen1, P. Bàrberi1, M. Raffaelli2, M. Mainardi3, A. Peruzzi2 & M. Mazzoncini2
1
Scuola Superiore Sant’Anna, Pisa, Italy, 2D.A.G.A.E., University of Pisa, Italy, 3Centro
Interdipartimentale di Ricerche Agro-ambientali E. Avanzi, S. Piero a Grado, Pisa, Italy
Abstract
As an alternative to chemical soil sterilisation and to soil solarization, the Italian company
Celli, in collaboration with the Department of Agronomy of the University of Pisa, has developed a
machine that is capable of sterilising the soil with hot vapour and the concurrent use of compounds
of low environmental impact that, by means of an exothermic reaction, increase the amount of heat
generated in the soil. In this study, the machine’s effect on the emergence of autumn-germinating
weeds was tested by studying the size and composition of the weed seedbank in two soil layers (010 cm and 10-20 cm) after different treatments. Soil samples were kept in a non-heated glasshouse
for 6 months and weed seedling emergence was monitored periodically. The field experiment
consisted in a factorial combination between two soil cover treatments (bare soil vs black
polyethylene film cover), two activating compounds (CaO vs KOH) and five rates of these
compounds (0, 1000, 2000, 3000 and 4000 kg ha-1). Analysis of variance was used to determine the
effect of treatments on seedling density and linear regression analysis to determine any correlations
between seedling density and compound application rate. Redundancy Analysis (RDA) was used to
detemine the effects of the various treatments on weed flora composition. In both soil layers, KOH
use resulted in a higher reduction in total weed seedling density than CaO use. In particular, a
significant reduction in density was observed for Capsella bursa-pastoris with increasing
compound application rate. The soil steaming treatments did not substantially influence weed flora
composition.
Introduction
Soil solarization was developed as an alternative method for soil sterilisation in order to reduce
the use of pesticides for pathogen control. Different sorts of plastic films can be used to increase the
heating effect of solar radiation. Besides pathogen control, increase in soil temperature by
solarization appeared to have a positive side-effect on insect and weed control and several studies
have been carried out to determine the best type of plastic sheet for optimising the weed control
effect (Habeeburrahman & Hosmani, 1996; Chase et al., 1999; Mudalagiriyappa et al., 1999).
However, soil solarization can only be used in summer in areas with enough radiation intensity to
produce a significant control effect.
A negative aspect of soil solarization is the long duration of the period in which the field
remains uncultivated, up to three months (Ricci et al., 1999). An alternative to the use of pesticides
and solarization techniques for soil sterilisation is the use of hot water vapour (steam). This
technique is used in horticulture, especially in glasshouses, but has never been considered as a
possible technique to be used under field conditions. The Italian company Celli, in collaboration
with the Agricultural Engineering Sector of the Department of Agriculture of the University of Pisa,
has developed a machine that is capable of sterilising the soil with hot water vapour in combination
with exothermic compounds of low environmental impact able to increase the heat produced in the
soil (Peruzzi et al., 2002). After treatment, the soil is immediately covered with a black plastic film
to increase the duration of the heating. The exothermic substances used are potassium hydroxide
(KOH) and calcium oxide (CaO). During initial assessment of the impact of potassium hydroxide
231
on the soil, a significant increase in soil exchangeable potassium and pH was registered; besides the
exothermic reaction, a caustic effect of KOH was also observed (Peruzzi et al., 2000). The present
study discusses the first results of an experiment set up with the objective to test this machine’s
effect on the germination capacity of autumn-germinating weeds by studying the size and
composition of the weed seedbank after different kinds of treatments. Preliminary data on treatment
effects on the actual weed flora are reported by Bàrberi et al. (2002).
A field experiment was laid out at the Centro Interdipartimentale di Ricerche Agro-ambientali
‘E. Avanzi’ at S. Piero a Grado, near Pisa (Lat. 43°40’ N; Long. 10°19’ E) on a sandy soil (sand
>91%) with a pH of 7.5 (for other soil characteristics see (Bàrberi et al., 2002)).
The field experiment consisted in a factorial combination between two soil cover treatments
(bare soil vs black polyethylene film cover, laid down by the machine right after soil steaming), two
activating compounds (CaO vs KOH) and five rates of these compounds (0, 1000, 2000, 3000 and
4000 kg ha-1). Two control treatments, with or without soil cover, were also included, giving a total
of 20 treatments, each replicated six times. Plot size was 5 x 1.2 m. Just before the steaming
treatment, the seedbed was carefully prepared to ensure maximum smoothness of the soil surface
and thus maximum theorical effect of steaming. Soil steaming was performed on 23 October 2000.
Soil temperature was monitored in selected plots at 15 cm depth for 180 minutes after vapour
treatment. Maximum soil temperature that was reached under the different treatments varied
between 75 and 85°C. On the day after the treatment, the soil was sampled for seedbank analysis to
test whether soil steaming might have induced a significant reduction in weed seedling recruitment
from buried seed reserves. Three soil cores of 20 cm depth were taken in each plot by means of a
3.5 cm diameter manual steel probe and immediately sub-divided in 0-10 and 10-20 cm subsamples for the assessment of steaming effect on seeds located at different soil depths. The weed
seedbank was analysed with the seedling emergence technique (Bàrberi & Lo Cascio, 2001). The
samples were allocated in plastic tubs over a 2 cm-thick layer of sterilized coarse sand and kept in a
non-heated glasshouse for six months under optimum moisture conditions. Drought periods were
periodically applied to stimulate seed dormancy breakage. Emerged weed seedlings were
periodically identified, counted and then removed.
For statistical analysis, total number of seedlings emerged in the three samples of each plot
were considered as a replicate. Weed seedling density was square-root-transformed before
ANOVA. Differences between means were calculated using LSD at the 5% significance level.
Redundancy Analysis (RDA) with forward selection of the environmental variables (ter Braak &
Smilauer, 1998) was used to analyse the treatment effects on the weed community composition
based on arcsine-transformed species relative abundance data. Treatments were inserted as
environmental variables during indirect gradient analysis and the six replicates were considered as
covariables. A Monte-Carlo permutation test was performed to calculate which of the treatments
contributed significantly to the explanation of the variation in the data set.
Results
Soil temperature
Table 1 shows that for the vapour treatment without any exothermic compound the soil
temperature never reached 80°C and after 180 min it was cooled down below 40°C. The use of an
exothermic substance, also at low concentrations, had a positive effect on the maximum soil
temperature. The use of higher concentrations of exothermic substances in the soil prolonged the
232
duration of higher soil temperatures. Differences between the exothermic effect of CaO and KOH
were very small and likely to be circumstantial.
Table 1. Maximum temperature registered, temperature reached after 180 min and average duration
of soil temperature above certain values in the first 180 min after soil steaming (15 cm
depth) for the vapour alone treatment and vapour + two exothermic compounds applied at
1000 and 4000 kg ha-1.
Temperature
Treatment
Vapour
Tmax (° C)
T after 180 min (°C)
T > 35°C (min)
T > 40°C (min)
T > 45°C (min)
T > 50°C (min)
T > 55°C (min)
T > 60°C (min)
T > 70°C (min)
T > 80°C (min)
74.9
36.6
>180
122
72
47
29
19
7
0
KOH 1000
80.5
41.0
>180
>180
104
59
35
21
8
4
KOH 4000
80.8
40.0
>180
>180
101
65
41
29
14
5
CaO 1000
80.3
38.8
>180
161
83
53
35
24
11
5
CaO 4000
85.5
41.6
>180
>180
120
72
46
32
17
7
0-10 cm layer
Analysis of variance of the cumulative number of seedlings m-2 emerged in the 0-10 cm layer
showed no effect of soil cover treatment and a significant (Pd0.01) interaction between the
exothermic compound used and application rate. Fig. 1 shows a significant negative relationship
between KOH and CaO application rate and total seedling emergence (r2 = 0.98 and 0.89
respectively). The use of vapour without any exothermic compound resulted in emergence of over
3800 seedlings m-2. With increasing rates of KOH, this number decreased significantly till less than
1000 seedlings m-2 (76% reduction), while the highest rate of CaO still resulted in emergence of
more than 3000 seedlings m-2 (20% reduction). Regression equations show that for any additional
100 kg ha-1 of exothermic compound used, KOH resulted in a reduction of 58 seedlings m-2 more
than CaO. A t-test performed between the average number of seedlings m-2 emerged in the control
plots without vapour (4417 seedlings m-2), and in the plots treated with vapour only (3840 seedlings
m-2) showed that the use of vapour without addition of exothermic compounds did not reduce
seedling emergence significantly.
233
Fig. 1. Regression of seedling density on CaO and KOH application rate in the 0-10 cm layer. * =
significant at P0.05, ** = significant at P0.01.
In the 0-10 cm layer a total of 19 weed species was recorded. The 8 major weed species, each with a
relative abundance greater than 1%, accounted for 97% of the total weed seedling density: Capsella
bursa-pastoris (60%), Lamium purpureum (12%), Veronica hederifolia (9%), Portulaca oleracea
(8%), Sonchus spp. (3%), Chenopodium album (1%), Poa spp. (1%) and Cyperus spp. (1%).
RDA demonstrated that replicates are responsible for 4% of the variation in species data,
whereas the treatments explained 5%. This means that the weed species composition is for 90%
dependent on other factors than the experimental treatments. Forward selection and the combined
Monte-Carlo permutation test demonstrated that KOH application rate explains 3% of the variation.
The other treatments did not contribute significantly to the explanation of the variation in the
species data.
Analysis of variance of the seedling density for the 4 major weed species showed a significant
compound by application rate interaction for C. bursa-pastoris whereas seedling density of L.
purpureum and of P. oleracea was not influenced by any of the treatments (data not shown). V.
hederifolia density was significantly lower in plots treated with potassium hydroxide than in those
treated with calcium oxide and higher application rates significantly reduced V. hederifolia density
with respect to the vapour-only treatment (data not shown).
10-20 cm layer
Analysis of variance of the number of
seedlings m-2 emerged in the 10-20 cm
layer showed no significant interactions
between the treatments and only a
significant (Pd0.01) effect of application
rate of the activating compounds used. Fig.
2 shows a significant negative relationship
between KOH application rate and
seedling emergence (r2 = 0.87), while that
between CaO application rate and seedling
emergence was not significant (r2 = 0.31).
The vapour treatment alone, in absence of any
exothermic compound, resulted in the emergence
of over 4200 seedlings m-2. With increasing rates
of KOH, this number decreased significantly until
d 2000 seedlings m-2 (55% reduction), while the
CaO application rate had no determined effect on
seedling emergence. A t-test performed between
the average number of seedlings m-2 emerged in
the control plots without vapour (7305 seedlings
m-2), and in the plots treated with vapour alone
(4215 seedlings m-2), shows that the use of vapour
234
without addition of exothermic compounds
did
significantly
reduce
seedling
emergence.
Fig. 2. Regression of seedling density on
application rate of KOH and CaO in the
10-20 cm layer. * = significant at P0.05,
ns = not significant.
In the 10-20 cm layer a total of 15 species was recorded. The 8 major weed species, each with a
relative abundance greater than 1%, accounted for 98% of the total weed seedling density: Capsella
bursa-pastoris (59%), Lamium purpureum (14%), Veronica hederifolia (11%), Portulaca oleracea
(8%), Poa spp. (2%), Chenopodium album (1%), Sonchus spp. (1%) and Tribulus terrestris (1%).
RDA demonstrated that replicates as well as treatments are responsible for 5% of the variation
in species data. Forward selection and the combined Monte-Carlo permutation test demonstrated
that none of the treatments contributed significantly to the explanation of the variation in the species
data.
Analysis of variance of the seedling density for the four most abundant weed species, C. bursapastoris, L. purpureum, P. oleracea and V. hederifolia, showed that their seedling density was
significantly lower in plots where an exothermic compound was used than in the vapour-only plots,
independent of the type of compound used (data not shown).
Discussion
In both the upper and lower soil layers the presence of a black polyethylene film cover did not
have any effect on weed seedling emergence. The effect of soil steaming on seedling emergence
was stronger in combination with potassium hydroxide than with calcium oxide. The former
resulted in a significant reduction in seedling emergence in both the upper (0-10 cm) and lower (1020 cm) soil layers with increasing application rate, while the latter reduced seedling emergence only
in the upper soil layer (Figs 1 and 2).
At higher application rates of calcium oxide and potassium hydroxide, soil temperature
remained above 40°C for more than three hours after vapour treatment. At the lowest calcium oxide
application rate temperature went below 40°C within three hours and in the vapour treatment
without addition of exothermic compounds within two hours. In bibliography there is little
reference to the soil temperature above which most weed species show increased seed mortality. In
a study on the effect of composting on weed seed germination (Nishida et al., 1998), germination of
15 weed species was reduced after composting for 7 to 25 days at temperatures above 46°C. At
temperatures above 57°C no seeds germinated. In a solarization study, soil temperatures of 45 to
65°C for 8-10 h per day during a 2 to 5 week period were considered effective to significantly
reduce weed seedling emergence (Horowitz et al., 1983). In other studies, daily temperature
235
fluctuation from 15 to 60°C in a dry environment for five months resulted in increased seed
germination (Baskin & Baskin, 1998). It seems that high temperatures in a dry substrate have less
effect on seed viability than in a humid substrate and that duration of high soil temperatures need to
persist for a relatively long time period in order to decrease seed viability. In this study soil
steaming was performed on a humid soil to enhance homogeneous heat distribution in the soil.
However, the maximum duration of temperatures above 45°C never exceeded two hours (Table 1).
This could have been due to easy heat dissipation in such an extremely sandy soil. It is not clear to
what extent this might have contributed to loss in seed viability. Despite the highest maximum
temperatures and longest persistence in the soil, the CaO treatment at 4000 kg ha-1 had a weaker
effect on seedling emergence than the KOH treatment at the same rate. The vapour alone treatment
reached slightly lower temperatures than the treatments with an exothermic compound, but it had no
significant effect on seedling emergence. This indicates that besides temperature another factor was
responsible for the higher decrease in seedling emergence with KOH use. This factor is thought to
be the direct caustic effect of this compound (Peruzzi et al., 2000).
In both soil layers, soil steaming in combination with use of potassium hydroxide significantly
reduced C. bursa-pastoris, while seedling emergence of C. bursa-pastoris, V. hederifolia and P.
oleracea was significantly lower at the highest application rates of the activating compounds than
after the vapour alone treatment.
In some soil solarization studies it has been suggested that annual weeds are more sensitive
than perennials (Horowitz et al., 1983; Chase et al., 1998). In the present study, no conclusions can
be drawn on the difference in sensibility to soil steaming of annual and perennial species because
the four major weed species were all annuals or biennials. Furthermore, seed size does not seem to
play a role because the seeds of V. hederifolia are the biggest ones (2-3 mm) and they responded
well to the soil steaming treatment. It seems that soil steaming has a general effect on all four
major, autumn-germinating, weed species in this study. Similar results were found for the major
weed species in soil solarization studies (Stapleton & De Vay, 1986; Vizantinopoulos & Katranis,
1993; Temperini et al., 1998). In general, soil steaming with exothermic compounds has a very
small effect on the weed species composition in the upper 20 cm of the soil.
Acknowledgements
This study was funded by Celli. We wish to thank M. Ginanni and the staff of the Centro
Interdipartimentale di Ricerche Agro-ambientali E. Avanzi of the University of Pisa for their
precious assistance in running the experiment and sampling.
References
BÀRBERI P & LO CASCIO B (2001) Long-term tillage and crop rotation effects on weed
seedbank size and composition. Weed Research 41, 325-340.
BÀRBERI P, MOONEN AC, RAFFAELLI M, PERUZZI A, BELLONI P & MAINARDI M
(2002) Soil steaming with an innovative machine - effects on actual weed flora. In:
Proceedings 5th Workshop of the EWRS Working Group on Physical and Cultural Weed
Control, Pisa.
BASKIN CC & BASKIN JM (1998) Seeds: Ecology, Biogeography and Evolution of Dormancy
and Germination. Academic Press, San Diego, California.
CHASE CA, SINCLAIR TR, SHILLING DG, GILREATH JP & LOCASCIO SJ (1998) Light
effects on rhizome morphogenesis in nutsedges (Cyperus spp): implications for control by soil
solarization. Weed Science 46, 575-580.
236
CHASE CA, SINCLAIR TR & LOCASCIO SJ (1999) Effects of soil temperature and tuber depth
on Cyperus spp. control. Weed Science 47, 467-472.
HABEEBURRAHMAN PV & HOSMANI MM (1996) Effect of soil solarization in summer on
weed growth and yield of succeeding rainy-season Sorghum (Sorghum bicolor). Indian Journal
of Agronomy 41, 54-57.
HOROWITZ M, REGEV Y & HERZLINGER G (1983) Solarization for weed control. Weed
Science 31, 170-179.
MUDALAGIRIYAPPA, NANJAPPA HV & RAMACHANDRAPPA BK (1999) Effect of soil
solarization on weed growth and yield of kharif groundnut (Arachis hypogaea). Indian Journal
of Agronomy 44, 396-399.
NISHIDA T, SHIMIZU N, ISHIDA M, ONOUE T & HARISHIMA N (1998) Effect of cattle
digestion and of composting heat on weed seeds. Japan Agricultural Research Quarterly 32,
55-60.
PERUZZI A, RAFFAELLI M, DI CIOLO S et al. (2000) Messa a punto e valutazione preliminari
di un prototipo per la disinfezione del terreno per mezzo di vapore e di sostanze a reazione
esotermica. Rivista di Ingeneria Agraria 4, 226-242.
PERUZZI A, RAFFAELLI M, GINANNI M & MAINARDI M (2002) Development of innovative
machines for soil disinfection by means of steam and substances in exothermic reaction. In:
Control, Pisa.
RICCI MSF, DE ALMEIDA DL, RIBEIRO RDD et al. (1999) Cyperus rotundus control by
solarization. Biological Agriculture and Horticulture 17, 151-157.
STAPLETON JJ & DE VAY JE (1986) Soil Solarization: A non chemical approach for
management of plant pathogens and pests. Crop Protection 5, 190-198.
TEMPERINI O, BÀRBERI P, PAOLINI R, CAMPIGLIA E, MARUCCI A & SACCARDO F
(1998) Solarizzazione del terreno in serra-tunnel: effetto sulle infestanti in coltivazione
sequenziale di lattuga, ravanello, rucola e pomodoro. In: Proceedings XI Convegno Biennale
della Società Italiana per la Ricerca sulla Flora Infestante: "Il Controllo della Flora Infestante
nelle Colture Orticole", Bari, 213-228.
TER BRAAK CJF & SMILAUER P (1998) Canoco Reference Manual and User's Guide to Canoco
for Windows: Software for Canonical Community Ordination (Version 4). Microcomputer
Power, Ithaca, NY, USA.
VIZANTINOPOULOS S & KATRANIS N (1993) Soil solarization in Greece. Weed Research 33,
225-230.
237
Water-jet cutting for weed control
F. Fogelberg1 & A. Blom2
Swedish University of Agricultural Sciences,
1
Dept. Crop Science, POB 44, SE-230 53 Alnarp
2
Dept. Agricultural Engineering, POB 66, SE-230 53 Alnarp
mailto: Fredrik.Fogelberg@vv.slu.se
An introductory study of new techniques for weed control on hard surface areas was conducted
during summer 2001. We investigated three methods: UV-light, laser and water-jet cutting. Two of
these methods have already been studied by the Danish scientists, Heisel and Andreasen. The third
one, water-jet cutting, is a well known method for cutting of e.g. plastics, metal and paper in
industry.
Water-jet cutting is a precise and environmental friendly technique with low treatment costs. The
equipment is however expensive due to the need of a powerful water pump. Use of water is low,
typically 1-3 litres per minut.
Cutting with pressurized water could be used to control weeds on hard surface areas such as railway
embankments and roadsides, or to cut potato haulm or sugarbeets and carrots at harvest. The high
water pressure can easily cut through all kind of materials – even stainless steel of 0.1 m thickness if sand is added to the water to enhance the cutting effect.
We investigated three treatment speeds (1, 3 and 5 m s-1) and three water pressures (1000, 2000 and
3000 bar) using small plants of oilseed rape. No statistical analyses were cariied out. At 3000 bar
pressure the highest speed resulted in more cut plants. At all tested speeds the medium water
pressure (2000 bar) appeared to be better, i.e. resulted in increased number of cut plants, than the
other two pressures. The small-scale experiment was not designed to evaluate interactions between
pressure and treatment speed.
The results indicate that water-jet cutting can be a new method for physical weed control on hardsurface areas such as railway embankments or along roadsides. However, we need to perform
experiments investigating the effect of speed and pressure on various organic materials. Costs and
design of a mobile machine are also important issues to study.
References
FOGELBERG, F. & BLOM, A. 2001. Laser, UV-ljus och skärande vattenstråle som framtida
metoder för ogräsbekämpning [Laser, UV-light and water jet cutting as future weed control
methods]. Report 2001: 03, Swedish University of Agricultural Sciences, Dept Agricultural
Engineering, Alnarp, Sweden.
238
Soil steaming with an innovative machine – effects on actual weed flora
P. Bàrberi1, A.C. Moonen1, M. Raffaelli2, A. Peruzzi2, P. Belloni3 & M. Mainardi3
Scuola Superiore Sant’Anna, Pisa, Italy, 2D.A.G.A.E., Settore Mecanica Agraria, University of
Pisa, Italy, 3Centro Interdipartimentale di Ricerche Agro-ambientali E. Avanzi, S. Piero a Grado,
Pisa, Italy,
1
Abstract
A prototype of a self-propelled machine for soil disinfection by means of steam injection was
tested for weed control in the field against autumn-germinating weeds. The field experiment
consisted in a factorial combination between two soil cover treatments (bare soil vs. black
polyethylene film cover, laid down by the machine right after soil steaming), two activating
compounds (CaO vs. KOH), aimed to increase soil temperature by producing an exothermic
reaction, and five rates of these compounds (0, 1000, 2000, 3000 and 4000 kg ha-1). Two control
treatments, with or without soil cover, were also included, giving a total of 20 treatments, each
replicated six times. Soil steaming was performed on 23 October 2000. Soil temperature and
moisture were monitored in selected plots. Weed density was sampled by species in two fixed 25 x
30 cm quadrats per plot at six different times. Soil temperature increased with the addition of CaO
and KOH. Averaged over all treatments, the maximum weed control effect was reached 30 days
after soil steaming. At that time, the reduction in total weed density, compared to the uncovered
control, ranged between 25% (vapour alone without cover) and 56% (soil steaming without cover +
1000 kg ha-1 of CaO). Averaged over all sampling periods, weed control seemed favoured by the
addition of the activating compounds, but there was not a clear relationship between compound rate
and percent weed density reduction.
Introduction
High soil temperature has been proven to reduce problems linked to pests, diseases, and weeds.
Actually, increase in soil temperature above a certain threshold is the aim of soil solarization, a
well-known method of soil disinfection used in warm-temperate areas aimed to reduce reliance on
pesticide use (Sauerborn et al., 1989; Kumar et al., 1993). However, soil solarization has some
drawbacks, e.g. it can only be used in summer and where radiation intensity is high, and implies
temporary subtraction of land to agricultural production (Temperini et al., 1998). These drawbacks
can be overcome by the use of hot water vapour (steam), a technique common in glasshouse
horticulture, but that has not yet been proposed for use under field conditions.
Although potential use of soil steaming is theoretically spanned over a longer seasonal period
compared to soil solarization, this advantage may be counteracted by lower soil temperatures,
especially when steaming is not performed in summer. For this reason, any technical solution that
can increase soil heating and duration of high soil temperature should result in increased steaming
effectiveness. In this context, one possibility is to apply activating compounds (e.g. fertilisers or
amendments) that, by reacting with the vapour produced by the steaming machine, can considerably
increase soil temperature.
This paper reports preliminary results of a study aimed to evaluate the on-field weed control
potential of a steaming machine developed jointly by the Italian company Celli and the Agricultural
Engineering Sector of the Department of Agriculture at the University of Pisa (Peruzzi et al., 2002).
239
This study, that was targeted to control of autumn-germinating weeds and includes several rates of
two activating compounds, is part of a larger study which also takes into account soil steaming
effects on pests, diseases, soil nutrient dynamics, and microbial activity (Peruzzi et al., 2000).
Results on treatment effects on weed seedbank size and composition are reported elsewhere
(Moonen et al., 2002).
A field experiment was conducted on a sandy soil at the Centro Interdipartimentale di Ricerche
Agro-ambientali E. Avanzi of the University of Pisa, located at S. Piero a Grado (Lat. 43°40’ N,
Long. 10°19’ E). Average soil characteristics were: clay 4.6%, silt 4.0%, sand 91.4% (USDA
classification), pH 7.5, total N (Kjeldahl) 0.086%, organic matter (Walkley-Black) 0.94%,
assimilatable P (Olsen) 10.6 ppm.
The experiment consisted in a factorial combination between two soil cover treatments (no
cover vs. black polyethylene film cover, which was laid down by the machine immediately after
soil steaming), two activating compounds (CaO vs. KOH) and five rates of these compounds (0,
1000, 2000, 3000 and 4000 kg ha-1). Two control treatments (with or without soil cover), were also
included, giving a total of 20 treatments, each replicated six times in 5 x 1.2 m plots. Prior to
steaming (carried out on 23 October 2000), the seedbed was carefully prepared to ensure maximum
smoothness of the soil surface and thus maximum theorical treatment effect. Soil temperature and
moisture were monitored in selected plots at 15 cm depth for 180 minutes after vapour treatment.
Weed density was sampled by species in two fixed 25 x 30 cm quadrats per plot at six different
times after soil steaming (10 and 23 November 2000, 8 December 2000, 5 January 2001, 8 February
2001, and 15 March 2001), and then referred to unit area.
Here, average data on percent reduction in total weed density (as compared to the "true"
control, i.e. that without soil cover) are reported, to allow a quick glance on the weed control
potential of steaming.
Results
Maximum soil temperature that was reached under the different treatments varied between 75
and 85°C (Moonen et al., 2002). Compared to vapour alone, application of the activating
compounds increased temperature duration above 45°C, an effect threshold proposed by Horowitz
et al. (1983) for soil solarization.
Mean initial total weed density in the control plots was 127.3 plants m-2. Averaged over all
treatments, the maximum weed control effect was reached 30 days after soil steaming (data not
shown). At that time, the reduction in total weed density, compared to the untreated control without
cover, ranged between 25% (soil steaming without cover and additional compounds) and 56% (soil
steaming without cover and with addition of 1000 kg ha-1 CaO).
Averaged over all sampling dates, weed control seemed favoured by the addition of both CaO
and KOH. However, total weed control seemed unrelated to rate of the activating compounds
applied (Fig. 1).
240
Discussion
Percent reduction in total weed density as compared to the uncovered control was not very
high, and decidedly lower than that observed in the soil seedbank (Moonen et al., 2002). This
difference between the effect on actual and potential weed flora may be partly due to serious soil
disturbance posed by the unusual heavy rainfall occurred during the experimental period (858.2 mm
between October 2000 and March 2001).
Compared to the initial weed density, percent weed reduction following steaming indicates that,
at the very best, still 78 plants m-2 survived the treatment, a quantity likely to require supplemental
weed control. However, just because of the unusual seasonal pattern, additional tests in more
standard weather conditions are needed before attempting to draw conclusions on the on-field effect
of steaming.
Weed seedbank data, obviously unbiased by adverse weather conditions, reflect in a much
clearer way the promising weed control potential of steaming (Moonen et al., 2002).
Covered check
10.5
36.4
KOH 4000
Treatments
KOH 3000
KOH 2000
18.2
23.8
28.5
KOH 1000
CaO 4000
22.3
28.3
CaO 3000
33.3
CaO 2000
38.9
CaO 1000
Vapour
19.6
% reduction
Fig. 1. Percent reduction (as compared to the uncovered control) in total weed density observed in
the different steaming treatments. Compound rates are in kg ha-1. Data have been averaged
over six sampling dates and, for the different rates and for vapour, over two soil cover
treatments (covered and uncovered).
Acknowledgements
Financial support for this study was provided by Celli. We wish to thank M. Ginanni and the
staff of the Centro Interdipartimentale di Ricerche Agro-ambientali E. Avanzi of the University of
Pisa for their precious help in running the experiment and data sampling.
241
References
HOROWITZ M, REGEV Y, HERZLINGER G (1983) Solarization for weed control. Weed
Science 31, 170-179.
KUMAR B, YADURAJU NT, AHUJA KN, PRASAD D (1993) Effect of soil solarization on
weeds and nematodes under tropical Indian conditions. Weed Research 32, 423-429.
MOONEN AC, BÀRBERI P, RAFFAELLI M, MAINARDI M, PERUZZI A & MAZZONCINI M
(2002) Soil steaming with an innovative machine – effects on the weed seedbank. In:
Control, Pisa, 11-13 March.
PERUZZI A, RAFFAELLI M, DI CIOLO S, MAZZONCINI M, GINANNI M, MAINARDI M,
RISALITI R, TRIOLO E, STRINGARI S & CELLI A (2000) Messa a punto e valutazioni
preliminari di un prototipo per la disinfezione del terreno per mezzo di vapore e di sostanze a
reazione esotermica. Rivista di Ingegneria Agraria 31, 226-242.
PERUZZI A, RAFFAELLI M, GINANNI M & MAINARDI M (2002) Development of innovative
machines for soil disinfection by means of steam and substances in exothermic reaction. In:
Control, Pisa, 11-13 March.
SAUERBORN J, LINKE KH, SAXENA MC, KOCH W (1989) Solarization: a physical control
method for weeds and parasitic plants (Orobanche spp.) in Mediterranean agriculture. Weed
Research 29, 391-397.
TEMPERINI O, BÀRBERI P, PAOLINI R, CAMPIGLIA E, MARUCCI A & SACCARDO F
(1998). Solarizzazione del terreno in serra-tunnel: effetto sulle infestanti in coltivazione
sequenziale di lattuga, ravanello, rucola e pomodoro. In: Proceedings XI Convegno Biennale
della Società Italiana per la Ricerca sulla Flora Infestante: “Il controllo della flora infestante
nelle colture orticole", Bari, 12-13 November, 213-228.
242
Hot water for weed control on urban hard surface areas
D. Hansson
Swedish University of Agricultural Science,
Department of Agricultural Engineering, P.O. Box 66, SE–230 53 Alnarp, Sweden
Introduction
Thermal weed control methods on hard surface areas based on hot water or flames are interesting
alternatives to herbicides and mechanical methods. They cause less wear on the treated surface
compared with mechanical methods like rotating wire brushes. However, flame weeding is not
possible to use in some areas i.e. on railroads, close to houses and parked cars, partly due to the risk
of fire. Hot water treatment eliminates the fire hazards associated with flame weeding. Hot water
equipment for weed control called Aqua Heat has been introduced in USA (Berling, 1992). In New
Zealand another hot water equipment for landscape and roadside vegetation management called
Waipuna System has been introduced. Preliminary studies showed that hot water killed most annual
and young perennial weeds, but older perennial weeds required repeated treatments (Daar, 1994).
Kurfess et al. (1999) and Kurfess & Kleisinger (2000) showed that the hot water method has a great
potential to be developed to control weeds in orchards.
Hot water weed control has been studied at the Swedish University of Agricultural Science. The
overall aim of these studies was to develop the hot water weed control method on hard surface areas
and study different kinds of parameters that have an influence on the weed control effect and dose.
For that reason experiments were carried out in laboratory, on arable fields and on hard surface
areas. The experiments were made on the test weed Sinapis alba L. (White mustard) in laboratory
and on arable fields, and on naturally developed weeds in the experiments on hard surface areas.
Dose-response relationships were described in order estimate the effective energy use and
effective travel speed of hot water treatment at different development stages and infestation levels.
Moreover, the influence of time of assessment of weed control effect (one or two weeks after
treatment), and the number of treatments needed during a season was studied (Hansson & Ascard,
manuscript).
The influence of weather conditions was studied in experiments with treatment at different airtemperatures, and after rain and after drought.
Some application technique parameters were studied to investigate the effects of water
temperature and drop size on hot water weed control (Hansson & Mattsson, Manuscript). The aim
in another experiment was to study if it is possible to decrease the required effective energy dose if
the time of exposure of the hot water is prolonged.
Results and discussions
The effect of hot water can be described by dose-response curves similar to those of flame
weeding and herbicides. The energy dose for a 90% reduction in plant weight was on Sinapis alba
L. in the 2-leaf stage one third of the energy required for the same reduction in the 6-leaf stage.
Treatment at an early stage saves energy, increases the driving speed and lowers the costs. A longer
lasting effect requires a higher energy dose. A 50% higher energy dose was needed to obtain a 90%
243
reduction in weed cover that lasted for 15 days instead of 7 days. Furthermore it was found that the
required number of treatments on hard surface areas was similar to that of flame weeding. Six hot
water treatments were needed during a vegetation season to obtain good weed control on an area
similar to gravel embankments with a well-established natural weed flora (Hansson & Ascard,
manuscript).
Preliminary results show that the weed control effect was not significantly different at different
air-temperatures (7 °C and 18 °C). This indicates that it is possible to compare results from studies
at air temperatures from 7 °C to 18 °C if other factors are constant. Rain before treatment increased
the required energy dose and drought decreased it.
In the study with different water temperatures it was shown that, at the same energy dose level,
the effect was generally higher at high temperature (Hansson & Mattsson, manuscript). The
explanation is probably that it is only the energy in the water above approximately 60 °C that is
effective in killing plants. Most plants die if they are exposed to temperatures above approximately
60 °C during a shorter period of time (Levitt, 1980). The higher the temperature in the water
applied, the higher is the proportion of the total energy in the water that can kill or damage weeds.
In another experiment there was a significant decrease in fresh weight per plant when the drop size
was increased (Hansson & Mattsson, manuscript). This probably depends on the fact that big
droplets do not cool down as fast as fine droplets. Prolonged time of exposure by an insulating sheet
mounted after the shield with nozzles increased the weed control effect, by probably decreasing the
plants cooling down rate.
References
BERLING J (1992) Getting weeds in hot water. A new hot-water weed sprayer and soy-based oil help
cut herbicide use. Farm Industry News 26, 44.
DAAR S (1994). New technology harnesses hot water to kill weeds. IPM Practitioner 16, 1-5.
HANSSON D & ASCARD J (manuscript). Influence of developmental stage and time of assessment on
hot water weed control. Submitted.
HANSSON D & MATTSON J E (manuscript) Effect of drop size, water flow, wetting agent and water
temperature on hot water weed control. Submitted.
KURFESS W, GUTBERLETT B & KLEISINGER S (1999). Hot water on weeds. Landtechnik 54, 148149.
KURFESS W & KLEISINGER S (2000). Effect of hot water on weeds. (in German with English
summary). Proceedings 20th German conference on weed biology and weed control. Stuttgart,
Hohenheim, Germany, 14 -16 March, 2000, Zeitschrift für Pflanzenkrankheiten, Pflanzenschutz
17, 473-477.
LEVITT J (1980) Responses to Environmental Stresses. Vol. 1. Chilling, Freezing and High
Temperature Stresses. 2nd ed. Physiological Ecology. Academic Press. (USA).
244
Thermal control of Vicia hirsuta and Vicia tetrasperma in winter cereals
P. Juroszek, M. Berg, P. Lukashyk, U. Köpke
Institute of Organic Agriculture, University of Bonn, Germany
Abstract
Vicia hirsuta and Vicia tetrasperma are troublesome weeds in organic winter cereal production in
Germany. Field experiments were conducted in western Germany, near Bonn, to evaluate the optimal
ground speed and application timing of an infrared (IR) weeder to control Vicia hirsuta and Vicia
tetrasperma efficiently, without significant reduction of crop yield. Heat application was postemergence of the crop. Two trials were conducted, in winter rye and winter wheat respectively. Each
trial consisted of three sections where thermal weed control was applied at three different growth
stages (winter wheat EC 22, EC 25, EC 31; winter rye EC 29, EC 30, EC 32). Each section was
arranged as a one-factorial block design with three replications. The tractor mounted IR weeder was
tested at 3 ground speeds (control plots without heat application, 1.5 km h-1, 1.0 km h-1, 0.5 km h-1).
The natural weed flora during tillering-phase of winter cereals comprised different annual species (e.g.
Veronica hederifolia) including a mixture of Vicia hirsuta and Vicia tetrasperma between one-leaf and
four-shoot growth stage. As expected, IR radiation after growth stage EC 29 of winter cereals was not
effective in reducing the number and fitness of Vicia species due to shading effect of the taller crop
plants, preventing that effective amounts of heat reached the smaller weed plants under the crop
canopy. Moreover, heat application at EC 31 and EC 32 resulted in severe grain yield loss of both
winter rye and winter wheat. On the other hand IR radiation at 0.5 km h-1 ground speed efficiently
controlled number and seed production of Vicia species when undertaken at tillering stages of winter
cereals, without reducing grain yield significantly. Moreover, winter wheat yield after IR radiation at
EC 25 was increased, possibly due to higher harvest index of the crop compared to the untreated
control. Results suggest that Vicia hirsuta and Vicia tetrasperma can be controlled between one-leaf
and four-shoot stage successfully in winter cereals, when heat is applied at EC 29 in winter rye and at
EC 22 and EC 25 in winter wheat respectively. Economic aspects of using thermal control methods in
winter cereal production are not discussed in this paper. However, due to high labour input and energy
consumption, application of IR radiation should be restricted to patches of Vicia species within a field
rather than overall.
Introduction
Vicia hirsuta and Vicia tetrasperma are troublesome annual weed species in cereals in organic farming
(Herrmann & Plakolm, 1991), but not under conventional farming conditions. Vicia species are
climbing legumes with a high competitive ability under low-nitrogen input conditions. Under lownitrogen input conditions crop plant densities are usually lower compared to conventional farming
conditions, resulting in more PAR reaching Vicia hirsuta leaves, increasing the competitive ability of
these species.
According to a survey by Eisele (1996) about 20 % of all organic farms in the German Bundesland
North-Rhine-Westphalia do have problems with Vicia hirsuta. Problems increase with duration of
organic production. If growing conditions are favourable they can completely cover the crop, resulting
in severe grain yield quantity and quality losses. An experiment by Roberts & Bodrell (1985) shows
that 11 % of seeds of Vicia hirsuta survived 5 years of burial time in soil without loosing their viability.
Seed accumulation of Vicia species in soils can create big problems for future cereal production and
should be avoided, at least be minimised. Particularly in winter cereals, Vicia species do have optimal
conditions for emergence and development because of autumn sowing, where germination can occur
245
after soil tillage and sowing. Moreover, if soil moisture is adequate, Vicia species are able to emerge
throughout the whole winter and early spring independent of soil disturbance (Juroszek, 2001
unpublished), possibly because of the large seed size that increase vigour (Milberg et al., 2000). This
observation is in agreement with Roberts & Bodrell (1985), who found Vicia hirsuta emerging from
October to May but scarcely at all in summer.
All factors that favour crop performance (e.g. high seeding density, narrow row width, high
shading ability of cultivar, nitrogen fertilisation) are adequate to decrease competitive ability of Vicia
species (Rademacher, 1937; Eisele, 1998). However, there are studies suggesting that Vicia hirsuta can
not be controlled efficiently by indirect measures alone (Drews et al., 2002). Even repeated mechanical
control with a harrow or a hoe is sometimes not effective (Eisele, 1998). According to a recent
literature survey there are no data available on control of Vicia species in winter cereal crops by using
thermal weed control methods. The efficacy of thermal weed control methods is attributed to a direct
effect of the heat on the cell membranes and to the indirect effect of subsequent desiccation (Vester,
1987). In 2001, a study was initiated to investigate whether an infrared (IR) weeder can be used to
control Vicia species seedlings efficiently, without decreasing winter rye and winter wheat grain yield
significantly. The main objectives of this study were to evaluate the ground speed of the IR weeder
required for effective control of Vicia species and to find the optimal timing of IR radiation for weed
control and crop tolerance.
Material and methods
Two field trials were undertaken, one in winter rye and winter wheat, respectively. Field trials were
located at Research Farm Wiesengut (eastern longitude 7 17‘, northern latitude 50 48‘, 65 m above sea
level) near Bonn, Germany. Average annual temperature is about 9.5 °C, average annual precipitation
700-750 mm. The soil type of field trials was silty loam. Winter rye was grown after spring wheat, and
winter wheat after potatoe. Each trial consisted of three sections, where thermal control was applied at
three different growth stages of the crop (winter rye EC 29, EC 30, EC 32; winter wheat EC 22, EC 25,
EC 31). Row width of winter rye was 12 cm, row width of winter wheat was 24 cm. The duration of
heat application was varied using different ground speeds of a tractor mounted IR weeder (control plots
without heat application, 1.5 km h-1, 1.0 km h-1, 0.5 km h-1). IR radiation was applied with a single
pass (Tab. 1). Each section was arranged as a one-factorial block design with three replications. Plot
size was 5 m long and 2.5 m wide. There was a 5 m border between plots to allow adjustment of the
ground speed of the IR weeder.
Table 1. Dates of IR radiation treatment, average weed density of Vicia species, minimum and
maximum air temperature, dates of assessments of different parameters in winter rye and winter wheat
Heat application
Winter rye
EC 29 (15th Feb.)
EC 30 (28th Mar. )
EC 32 (2nd May)
Winter wheat
EC 22 (15th Feb.)
EC 25 (28th Mar.)
EC 31 (2nd May)
Weed density
Vicia species
Plants m-2
Temperature
Min./max.
°C
Parameters
Crop and
weed injury
Ground cover
Crop harvest and Vicia
plant collection
45.3
Not assessed
Not assessed
-1/7
1/7
11/20
5th Mar.
4th Apr.
5th May
28th June
28th June
28th June
23rd July (by hand)
23rd July (by hand)
23rd July (combine)
13.1
21.1
Not assessed
-1/7
1/7
11/20
23rd Feb.
12th Apr.
5th May
22nd June
22nd June
22nd June
23rd July (by hand)
23rd July (combine)
23rd July (combine)
An IR weeder (company Görgens, Cologne, Germany, produced in year 1987) was used with gasphase burners directed backwards in front of a shielded grid. The working width of the IR weeder is
246
2.4 m, and the length of the IR weeder is 1.5 m. The energy source of the burners is liquid propane.
Liquid propane is delivered to a vaporiser before entering the burners. Heat produced by the burners is
transported to a grid made of manganese radiating the heat towards the soil surface. Maximum
temperature at the surface of the grid is about 900 °C. Gas pressure is 1.5 bar (0.15 MPa). Maximum
gas consumption is about 48 kg h-1 giving 616 KW. According to Ascard (1998) these kind of weeders
are flame weeders rather than IR weeders because they use burners with a open flame. The original IR
weeders do have non-catalytic atmospheric burners. However, in this paper the name IR weeder is
used, referring to the company Görgens, selling the thermal weeder used in this study.
The natural weed flora during the tillering-phase of the cereals consisted of different annual
species typical of winter cereal production (e.g. Galium aparine, Matricaria recutita, Apera spicaventi, Veronica hederifolia, Stellaria media) including a mixture of Vicia hirsuta and Vicia tetrasperma
between one-leaf and four-shoot growth stage. Plant height of Vicia species was about 5 cm. Weed
density and weed growth stage during elongation-phase of winter cereals was not assessed because it
was obvious before performing the heat treatment that the crop would shade the smaller weed plants.
The study focussed on evaluating the heat tolerance of crops rather than on weed control. Crop plants
were always taller than weed plants. The IR weeder was mounted slightly above the top leaves of the
crop plants. However, at EC 31 and EC 32 the crop plants were taller than the maximum height of the
tractor mounted IR weeder. The canopies of weeds and crops were dry at the time of IR radiation.
At the time of IR treatment, soil moisture and air temperature were recorded (Tab. 1). After
performing thermal weed control in winter rye at EC 29 and winter wheat at EC 22, there was frost
during the night, perhaps influencing the injury of crop and weed plants. Several days after conducting
IR weeding, the degree of injury to individual plants of Vicia species was estimated in three
randomized subplots (each 0.1 m2 area) per plot (Tab. 1). These subplots were used in all subsequent
assessments. Growth stage of individual plants was assessed for each Vicia species separately (effect of
growth stage of Vicia species on efficacy of IR weeding not shown). The degree of injury to crops was
estimated at the same time and position as Vicia species plant injury, but an overall estimate of damage
to all cereal plants within the frame was made rather than individual plant assessments. Percent ground
cover estimation of Vicia species was carried out on whole plot area. At crop harvest, ten Vicia hirsuta
plants were collected randomly in each plot to measure production of pods per plant. Harvest was
either carried out cutting the crop by hand from two randomised subsamples per plot, or a combine was
used (working width 1.5 m), harvesting the centre of each plot (Tab. 1).
Analysis of results was performed using the SAS statistical package (version 8.2). Subsamples
were pooled to obtain a block treatment average for each treatment, which was used in all subsequent
analysis (HURLBERT 1984). Results of % ground cover estimation, pod production of Vicia hirsuta and
yield parameters were statistically evaluated using analysis of variance (D = 0.05) based on a onefactorial block design model. Comparison of means was evaluated with Tukey’s test (D = 0.05).
Results
Effect of IR radiation on Vicia species applied during the elongation-phase of winter cereals
IR radiation applied after growth stage EC 29 of winter cereals did not reduce the number and fitness
of Vicia species at any ground speed. Possibly taller crop plants prevented effective doses of heat
reaching the smaller weed plants, which were located under the crop canopy. Particularly after heat
treatment at EC 31 and EC 32, winter cereal plants were seriously injured and the development of
weeds including Vicia species was enhanced due to the light that penetrated through gaps of destroyed
crop canopy.
247
Effect of IR radiation on winter rye and winter wheat applied during the elongation-phase
Heat application in winter rye at EC 30 resulted in moderate yield losses (up to 5.1 dt ha-1), whereas in
winter rye at EC 32 and in winter wheat at EC 31, severe losses of grain yield were recorded (winter
rye up to 17.1 dt ha-1 and winter wheat up to 18.7 dt ha-1). The later and the longer heat treatment was
applied, the bigger was the grain yield depression (Tab. 2). IR radiation at EC 32 reduced the number
of ears m-2 in winter rye by 75 ears m-2 compared to the control plots and in winter wheat at EC 31 by
up to 61 ears m-2. Thousand seed weight of grain was reduced in winter rye at EC 32 by up to 6.4 g,
and in winter wheat at EC 31 by up to 3.4 g, compared to the control. Ripening of cereal straw and
grains was retarded by one to two weeks.
Table 2. Grain yield (86% DM) after IR radiation applied at different crop growth stages during the
elongation-phase
Ground speed (km h-1)
0 (Control)
1.5
1.0
0.5
Winter rye (EC 30)
Grain yield (dt ha-1)
37.2
35.8
34.2
32.1
Winter rye (EC 32)
34.9 a
13.6 b
11.4 b
10.0 b
Winter wheat (EC 31)
51.8
40.3
36.8
34.7
(Results with different letters are significant, results without letters behind are not significant, Tukey’s test, D = 0.05)
The results of this study strongly suggest that winter rye and winter wheat were not able to recover
from injuries due to heat treatment when applied during their elongation-phase.
Effect of IR radiation on Vicia species applied during the tillering-phase of winter cereals
In contrast to the elongation-phase, IR radiation controlled density and seed production of Vicia species
efficiently when undertaken during the tillering-phase of winter cereals.
Growth stage of the cereals at treatment
Winter rye (EC 29)
100
60
40
20
on
tro
l
km
h -1
1.
0
km
h -1
0.
5
km
h -1
1.
5
C
on
tro
l
km
h -1
1.
0
km
h -1
0.
5
km
h -1
1.
5
1.
5
C
on
tro
l
km
h -1
1.
0
km
h -1
0.
5
km
h -1
0
C
Plants (%)
80
Losses of leaf area (%)
100
(lethal)
75 - 99
50 - 75
25 - 50
1 - 25
0
248
Figure 1. Leaf area injury of Vicia species plants treated at one-leaf to four-shoot stage in winter rye
and winter wheat with an IR weeder at different ground speeds
Figure 1 shows that IR radiation at 0.5 km h-1 ground speed was most effective in reducing the number
of Vicia species. The number of lethal plants after IR radiation increased with decreasing ground speed.
In winter wheat at EC 25, the ground speed of 1.5 km h-1 was not able to kill any Vicia species plant.
However, in winter rye at EC 29 and in winter wheat at EC 22, IR radiation at the same speed killed
few plants. Possibly, frost during the night after IR treatment increased the efficacy of IR application in
both cases.
Several weeks after the first assessment, plant injury was assessed a second time (data not shown)
revealing that a considerable number of Vicia species plants had emerged in treated and in control plots
since IR application. These data suggest that IR radiation had no influence on germination and
emergence of seedlings (data not shown). However, newly emerged weed plants after IR radiation
reduced the long-term effect of thermal weed control.
20
Ground cover (%)
Winter rye (EC 29)
13.3
13.0
11.6
10
9.9
9.2
9.2
7.7
5
4.9
5.7
4.7
5.7
0
Control
1.5 km h-1
1.0 km h-1
0.5 km h-1
Figure 2. Ground cover of Vicia species (assessed end of June) treated at one-leaf to four-shoot stage
in winter rye and winter wheat with an IR weeder at different ground speeds at different crop growth
stages (results are not significant, analysis of variance, D = 0.05)
The ground cover of Vicia species was estimated at the end of June. Ground cover estimations
confirmed the results of plant injury assessment. In general, IR radiation at ground speed 0.5 km h-1
gave the best control of Vicia species (Fig. 2). The efficacy of IR radiation at 1.5 km h-1 and 1.0 km h-1
in winter rye at EC 29 was poor, whereas in winter wheat at EC 22 these ground speeds reduced
ground cover of Vicia species compared to the untreated control. In winter wheat, IR radiation applied
at EC 25 using a ground speed of 1.5 km h-1 was as effective as using 0.5 km h-1 ground speed.
Figure 3 shows that IR radiation at 0.5 km h-1 ground speed reduced the number of pods compared
to the untreated control (results are not significant). In winter rye at EC 29, the average pod number per
plant was more than 300 in untreated control plots, whereas in plots treated with IR radiation at ground
speeds of 0.5 km h-1, pod number per plant was less than 200. However, in winter rye and in winter
wheat IR radiation applied at EC 22 using ground speeds of 1.5 km h-1 and 1.0 km h-1 also reduced pod
production of plants. In winter rye, ripeness of pods was delayed when IR radiation was applied at a
ground speed of 0.5 km h-1, suggesting that development of plants that survived heat treatment was
also delayed.
249
Winter rye (EC 29)
400
Pods per plant
300
2x SEM
200
100
Degree of ripeness:
green
Co
nt
ro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
Co
nt
ro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
Co
nt
ro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
0
brown
open
Figure 3. Pods of Vicia hirsuta (Vicia tetrasperma not measured) at harvest time of winter rye and
winter wheat treated with an IR weeder at different ground speeds (results are not significant, analysis
of variance, D = 0.05), SEM: Standard error of the mean
Effect of IR radiation on winter wheat and winter rye applied during the tillering-phase
All winter rye and winter wheat plants survived IR radiation when applied during the tillering-phase.
On the other hand all crop plants were injured because of IR radiation, but the degree of injury varied
(Fig. 4).
Winter rye (EC 29)
80
60
40
C
on
tro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
0
0
C
on
tro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
20
C
on
tro
1.
l
5
km
h -1
1.
0
km
h -1
0.
5
km
h -1
Crop leaf area (%)
100
Losses of leaf area (%)
1 - 25
25 - 50
50 - 75
75 - 99
Figure 4. Degree of injury to leaf area (%) of winter rye and winter wheat treated at different growth
stages with an IR weeder at different ground speeds
250
Leaf area injury was more pronounced in winter rye at EC 29 and winter wheat at EC 22 than in winter
wheat at EC 25, suggesting again that frost after IR application might have increased the effect of IR
radiation. Maximum leaf area injury (more than 75 % injured leaf area) was estimated in winter wheat
treated with IR radiation at EC 22 at ground speed 0.5 km h-1. The injured leaf area of winter wheat
plants treated at EC 25 did not exceed 25 % at any ground speed.
Grain yield (86 % DM) and the various yield parameters of winter rye and winter wheat were not
significantly affected by IR radiation applied at different growth stages during the tillering-phase.
Moreover, winter wheat yield after IR radiation at EC 25 was increased, possibly due to higher harvest
index compared with the untreated control. However, it might be that yield was not directly increased
due to heat treatment, but was increased indirectly because of good weed control.
Table 3. Grain yield (86 % DM) and yield parameters of winter rye and winter wheat treated with IR
radiation at different ground speeds at different growth stages during tillering-phase
Winter rye (EC 29)
-1
Ground speed (km h )
0
1.5
1.0
0.5
0
1.5
1.0
0.5
0
1.5
1.0
0.5
298
297
283
287
451
424
440
399
437
424
466
434
45.3
47.7
44.6
45.0
26.9
29.3
28.3
29.8
29.1
32.0
30.9
34.9
28.4
28.6
28.6
29.2
47.1
46.2
46.0
46.5
47.2
48.5
47.0
47.2
Grain Yield (dt ha )
39.9
40.6
34.6
37.6
57.0
57.3
57.2
55.2
60.0
65.9
67.5
71.6
Harvest index
0.39
0.39
0.38
0.38
0.46
0.48
0.48
0.49
0.46
0.49
0.51
0.52
Ears m-2
-1
Seeds ear
TSW (g)
-1
(Results are not significant, analysis of variance, D = 0.05)
Table 3 shows that winter rye and winter wheat were able to recover from injuries caused by heat
treatment when applied during tillering-phase (winter rye at EC 29, winter wheat at EC 22 and EC 25)
under the given growing conditions.
Discussion
In this study an infrared (IR) weeder was used to control Vicia species in organically grown winter
cereal crops. This weeder was chosen because the system was available at Wiesengut Research Farm.
If farmers do have a thermal weeder available without the need to buy it, it might be profitable to use
the weeder not only in vegetables like onions and carrots with high market value, but also in winter
cereals. However, thermal control methods are labour intensive (Nemming, 1994). If farmers cultivate
large areas of cereals it would take a too long time to apply IR radiation efficiently. However, many
weed species are not distributed homogeneously at the field (Gerhards et al., 1996) but are located
within patches at high plant densities. Thermal weed control methods in cereal crops should be applied
only to those patches to reduce costs and labour input. Using IR radiation to control less competitive
weed species can not be recommended, but it might be profitable to use thermal control tactics to
reduce number and fitness of serious weed species that are able to cover cereal plants completely, such
as Vicia hirsuta and Vicia tetrasperma.
The crops tested in this study are monocots, known to be tolerant to thermal control methods at
certain growth stages (Vester, 1987). The appropiate timing of thermal application is important for
effective use, both to control weed species efficiently and to minimise crop injury. In this study it was
possible to control Vicia species between one-leaf and four-shoot stage with post-emergence IR
radiation in winter rye and winter wheat during the tillering-phase of crops, without significant yield
losses. However, IR radiation during the elongation-phase of crops resulted in poor weed control and
big losses of grain yield. Taller crop plants shaded the smaller weed plants, preventing that effective
251
doses of heat reaching Vicia species. In particular IR weeders are less effective than flame weeders in
dense vegetation, where shading occurs (Ascard, 1998).
Thermal weed control in this study was only applied once. After IR application several seedlings
of Vicia species emerged, reducing the long-term effect of this control method. Late emerging weeds
are the main reason for repeated heat treatments (Vester, 1987). The long-term effect of flaming
depends largely on the extent of weed emergence after treatment (Parish, 1990, Ascard, 1992).
Sequential treatments might be a solution to overcome the problem of late emerging weeds (Ascard,
1995). However, split treatments are labour intensive and can not be recommended for use in winter
cereal production. Therefore, thermal weed control should be applied later in order to contact as many
weed plants as possible, although not all weed plants will be at their most susceptible stage (Ascard,
1995).
It was expected that in general thermal weed control would reduce grain yield of winter cereals.
However, winter wheat treated at all ground speeds with IR radiation at growth stage EC 25 resulted in
higher grain yields than the untreated control. A likely explanation is that at this growth phase winter
wheat was tolerant to injuries caused by heat treatment. The harvest index of winter wheat suggested
that thermal weed control reduced the vegetative growth of winter wheat, whereas grain production
was enhanced. However, an adequate explanation why grain production was enhanced is not possible,
because results of yield parameter assessments are contradictory. In one case (IR treatment at ground
speed 1.0 km h-1) the number of ears m-2 was enhanced, in another case (IR treatment at ground speed
0.5 km h-1) the number of seeds ear-1 was enhanced (Tab. 3). However, it might be that yield was not
directly increased due to heat treatment, but was increased indirectly because of good weed control.
Further field trials will prove if the developmental stage EC 25 is the most heat tolerant stage and most
suitable to apply thermal control methods in winter cereals.
Other questions arised in this study: Winter wheat plants treated at EC 25 were only moderately
injured, whereas plant injuries of winter rye treated at EC 29 and winter wheat plants treated at EC 22
were much more injured. One possible explanation is that frost after heat treatment did increase the
degree of crop injuries. If so, heat treatments should not be applied, if frost is forecasted. On the other
hand frost would increase the efficacy of heat treatment, because injured plants would be killed due to
low temperatures, otherwise they would survive the heat treatment. Water status of plant cells can
influence results of heat treatments (Ascard, 1995). However, dry matter of crop plants at the time of
heat treatment was not assessed in this study. In future studies this parameter should be measured in
detail.
The effect of IR radiation on Vicia hirsuta and Vicia tetrasperma plants was highly variable, too.
For example, IR radiation treated at 0.5 km h-1 ground speed killed plants, injured plants severely, but
injured other plants only slightly. It might be that different developmental stages of Vicia species plants
influenced efficacy of heat treatment. Observations suggest, that shading effects of crop plants and soil
structure might influence efficacy of IR radiation. Vicia species plants were small at the time of heat
treatment and were shaded by taller crop plants. Particularly, if weed plants are located in the row of
the crops they could be easily shaded by crop canopy, preventing that effective doses of heat could
reach them. It might be that flame weeders would overcome this problem, because they are more
effective than IR weeders, when shading effects occur (Ascard, 1998). Further field trials will test the
efficacy of flame weeders to control Vicia species plants in winter cereals. Moreover, soil structure can
influence the extent to which heat penetrates to weed plants (Parish, 1990). Soil structure was rough
after sowing, both in winter rye and winter wheat, creating slots in the soil, where Vicia plants were
located. It might be that IR radiation was less effective in reaching weed plants in those slots.
Vicia hirsuta and Vicia tetrasperma plants were able to regrow from basal based buds, in spite of
severe stem and leaf area injuries. The capacity of regrowth largely depends on environmental
conditions like soil moisture after heat treatment (Vester, 1987). The soil after heat treatment in this
study was moist for a long time, perhaps contributing to a high regrowth capacity of Vicia hirsuta and
Vicia tetrasperma.
252
It can be concluded that optimal application of thermal control methods should take into account
growth stage of target weeds, growth stage of the crop, emerging time of weed species, regrowth
capacity of target weed species and environmental conditions before, during and after heat treatment.
Acknowledgements
We thank Dr. D H K Davies from the Scottish Agricultural College for valuable comments on the
manuscript. The research is part of the project ’Problemunkräuter im Organischen Landbau:
Entwicklung von Strategien zur nachhaltigen Kontrolle von Ackerkratzdistel Cirsium arvense und
Rauhhaariger Wicke Vicia hirsuta’ funded by the Ministry of Environment, Agriculture and Consumer
protection of Province North-Rhine-Westphalia. Technical support by Johannes Siebigteroth, Henning
Riebeling and Frank Täufer is greatfully acknowledged. We are indebted to the many students assisting
our research team.
References
ASCARD J (1995) Effects of flame weeding on weed species at different developmental stages. Weed
Research 35, 397-411.
ASCARD J (1998) Comparison of flaming and infrared radiation techniques for thermal weed control.
DREWS S, NEUHOFF D, JUROSZEK P & KÖPKE U (2002) Einfluss von Sortenwahl, Reihenweite und
Drillrichtung auf die Konkurrenzkraft von Winterweizen im Organischen Landbau. Zeitschrift für
Pflanzenkrankheiten und Pflanzenschutz, Sonderheft XVIII, 527-532.
EISELE J-A (1996) Vicia hirsuta (L.) S.F. Gray – Problemunkraut des Organischen Landbaus.
Zeitschrift für Pflanzenkranheiten und Pflanzenschutz, Sonderheft XV, 225-231.
EISELE J-A (1998) Strategies for the control of Vicia hirsuta (l.) s.F. Gray in Organic Farming. Med.
Fac. Landbouww. Uni. Gent 63 (3a), 705-711.
GERHARDS R, WYSE-PESTER DY & MORTENSEN DA (1996) Characterising spatial stability of weed
populations using interpolated maps. Weed Science 45, 108-119.
HERRMANN G &, PLAKOLM G (1991) Ökologischer Landbau. Österreich. Agrarverlag, Wien.
HURLBERT SH (1984) Pseudoreplication and the design of ecological field experiments. Ecology and
Monograph 2, 187-211.
JUROSZEK P (2001) Institute of Organic Agriculture, University of Bonn, Germany, unpublished.
MILBERG P, ANDERSSON L & THOMSON K (2000): Large-seeded species are less dependent on light for
germination than small-seeded ones. Seed Science Research 10, 99-104.
NEMMING A (1994) Costs of flame cultivation. Acta Horticulturae 372, Engineering for Reducing
Pesticide Consumption & Operator Hazards, 205-212.
PARISH S (1990) The flame treatment of weed seedlings under controlled conditions. Crop Protection
in Organic and Low Input Agriculture, BCPC Monograph No. 45. Farnham: British Crop
Protection Council, 193-196.
RADEMACHER B (1937) Gedanken zur Fortentwicklung der Unkrautbekämpfung im Getreide.
Pflanzenbau 14, 1937/38, 449-465.
ROBERTS A & BODDRELL JE (1985) Seed survival and seasonal pattern of seedling emergence in some
Leguminosae. Annals of Applied Biology 106, 125-132.
VESTER J (1987) Biologische Effekte des Abflammens in landwirtschaftlichen und gartenbaulichen
Produkten in Dänemark. In: Geier B & Hoffmann M, eds. Beikrautregulierung statt
Unkrautbekämpfung – Methoden der mechanischen und thermischen Regulierung. Alternative
Konzepte 58. Karlsruhe, C.F. Müller Verlag, 153-166.
253
Thermal weed control by water steam
A. Sirvydas1, P. Lazauskas, R. Vasinauskienơ, P. Kerpauskas
Summary
The article presents original research on thermal weed control by water steam. Steam has a high
energy density and also a high heat transferring capability. Heat intensity increases 1000-2000
times in comparison to flaming by gas technology. Wet steam surrounding immediately increases
temperature of plant surface tissues; the influence is destructive. The biggest yield of barley grain is
received after steaming in phase of 2-3 leaves.
The thermal weed control technology is based on the plant thermoenergy exchange at high
temperatures. This technology uses the thermomethod for disturbing or pulling off the vital
functions of the over-ground part of a plant. The energy exchange between a plant and its
environment is a continuous process. The energy balance allows determining the individual
members of the balance, which have a different influence on the plant surface temperature in a high
- temperature environment.
Introduction
The thermal weed control technology by high temperature water steam is a new and very promising
one. The essence of the matter is that water steam thermodynamics quality in plant media may
change and is accompanied by change of convection heat exchange intensification from 1000 to
2000 times. This unusually big change is decisive for weed control by water steam efficiency and
economy.
Continuous energetic changes go on between plant and environment, where radiation, heat,
electromagnetic and ionization radiation take place. Trying to determine the influence of high
temperature environment on a plant energy balance of a plant (organ) should be analyzed. It
depends upon a lot of factors and mainly upon physical and thermo dynamical properties of plant
environment, physiological functions of plant organ, geometrical form of an organ, plant adaptation
to conditions of the examined environment. Plant energy balance in specially created high
temperature environment helps to determine the research direction creating effective means of
thermal weed control. On the other hand, it is important to identify the influence of basic factors to
be strengthened or weakened for the purpose of thermal plant destroying. A theoretical foundation
of high temperature environment creation possibilities for using weed control equipment that is
effective in ecological agriculture is necessary.
Aim of the work
The work aims to analyze the influence of high temperature media on a plant; to form usual energy
balance of a plant; to analyze plant organ energy balance; to determine energy balance of plant
organ in high temperature environment; to elucidate the basic factors, which determine energy
balance of a plant; to analyze energetic possibilities of a plant to adapt to unfavorably high
Correspondence: 1Sirvydas A., department of Heat and Biotechnology Engineering, Lithuanian University of Agriculture. 4324 Kaunas-Akademija,
Lithuania. Tel. (+370)-7- 397517, email: sirvydas@tech.lzua.lt
Lazauskas P., Department of Soil Management, Lithuanian University of Agriculture. 4324 Kaunas-Akademija, Lithuania. . tel. (+370)-7-397129,
email: Plazauskas@nora.lzua.lt
254
temperature environment; to investigate theoretical possibilities of effective weed control
technology creation in ecological agriculture and to present its theoretical foundations.
Estimation of the thermal processes in the plant
At present thermal weed control based on gas burning is used. The economical efficiency of this
process is very low and reaches only 1-2 . The other heat goes to technological loss or loss to the
environment. Which kind of high temperature media (moist air, hot water or water steam) is most
widely applied for thermal weed control, depends upon future technological studies, scientifical
substantiation and most important, the economy of the machinery (CESNA J, at all (2000)).
The process of heat restitution of high temperature media depends upon the thermokinetical
features of the media. Analyzis of this process shows that the temperature in heat media
surrounding a plant is constant tp const. At the initial moment the surface temperature of a plant
stem also is constant ts1 const, until it is not affected by steam of a plant temperature media.
At the initial moment of high temperature media influence, approaching to the surface of a plant
organ, there is a consecutive temperature fall to the temperature of a plant ts surface as shown in the
scheme A (fig. 1). At this moment the expenditure of heat is the greatest because of the difference
of the temperatures (tg-ts) between high temperature media and the surface of plant tissues. The
amount of the given back heat g(w) to the tissues of a plant surface F (m2) is found:
q aF(tf-ts)
(1)
Everything that is not clear and difficult to defer to in this process is hidden in the coefficient of
given back heat D W/(m2.K). This constant is particularly compound and depends upon many
variable factors. The characteristic feature is that this constant depends upon physical –
thermodinamical parameters and defines the intensity of process of this given back heat. Orientative
weaning is presented in table 1.
Table 1. Orientative meanings of the coefficient D W/(m2.K) of given back heat (INCROPERA
F.P., DEWITT D.P. (1981), DROBAVICIUS A. at all (1974)).
High temperature media heat affects a plant
Air, burning gas, overheat steam
Water
Damp eater steam in the process of condensation
D W/(m2.K)
5-50
200-3000
5000-100000
At using flaming by gas in thermal weed control the temperature difference (tg-ts) is greater and
it reaches 400-900 0C. At the same moment the temperature of the water and damp water steam
used for weed control (tg-ts) is only about 90 0C. In spite of high temperature the used method of
flaming by gas, the transfused steam q to the tissues of the plant remain 200 times less than
condensation water steam and about 5 times less than hot water (the transpiration of a plant is not
estimated) (Sirvydas A. Cesna J. (2000)).
When heat is provided to a plant the temperature of its surface rises and reaches ts2. The
difference between the temperatures of the media and the surface of the plant (tf-ts2) decreases
completely. The change (alteration) of the temperature ts1ots2 on the surface of the plant in the
heating process is shown in the scheme B (fig. 1). When the temperature on the surface of the plant
in ts2, the effectiveness of the process of thermal weed control depends upon the speed at which the
temperature
t, oC
A
255
t, 0C
B
tf
tf
tf
tf
t s2
t s2
q
q
q
q
t s1
t s1
t s1
0
l, m
l, m
t, 0C
C
q
tf
t s2
t s2
0
t s1
l, m
t, 0C
q
q
q
0
60 C
tf 1
l, m
ts
0
l, m
D
tf
ts
l, m
l, m
ts 3
ts 3
0
tf 1
l, m
Fig. 1 Temperature changes in the stem of a weed at the moment of damage. A - beginning of
heating. B - temperature change at the surface of the stem. C - temperature change in the stem at the
moment of heating. D - temperature change in the stem after the heating is stopped.
spreads in the tissues of a plant, that is upon the spreading of heat conductivity from superficial
plant tissues to deeper layers of plant tissues. This process is characterized by the coefficient of heat
conductivity of plant tissues O, W/(m.K). It is necessary to note that the coefficient of heat
conductivity of live tissues of a plant is low O 0,57 W/(m.K).That shows that the heat in the tissues
of plant spreads slowly. The temperature of deeper plant tissues is not reached quickly. The
temperature that destroys inner tissues of the plant (t 60 oC) is reached after some time. For this
reason in the use of thermal weed control for larger plants the time of high temperature influence is
prolonged. Having prolonged the time of influence, the speed of moving of equipment as well as its
economy decreases.
After the heating of the plant is stopped the process of temperature getting equal in the tissue of the
plant takes place: the surface of the plant is cooled by natural environment. The heat that has been
accumulated in the tissues of the plant is given back to the environment and to the temperature
wave to deeper tissues of the plant.
The tissues of the plant are destroyed at the temperature of 60 oC and at the exact moment the
temperature distributes in the tissues of the plant, which has destroying effect on the plant D (fig.1).
Plant organ energy balance
Extreme conditions are specially created for destruction or interruption of vital functions of the
plant by using thermo energy in its environment.
256
For examination of these high temperature conditions energy balance of organ or part of the
plant has been created. Plant organ energy balance equation can be written in the following way:
¦ Q Q
sp
Q atsp a f Q apl a apl rQ š Qtr r Qlaid Q f r Qta r Qvp
0.
(2)
This equation shows that the organ or part of the plant receives energy that comes from radiating
source (Qsp) and is reflected (Qatsp) from other bodies. The plant receives energy as infrared
radiation from environment and atmosphere (Qapl). This energy is partially absorbed. Parts of
absorbed physiological and long wave energy are pointed by af and aapl coefficients respectively.
The plant receives or gives back its energy for convectional heat exchanges with environment (Qs),
and uses the energy for transpiration (Qta), passes the heat to distant tissues by conduction (Qlaid),
uses it for photo chemical reactions and other endothermic processes (Qf). Thermo accumulation
(Qta) goes on in the plant tissues.
Plant energy balance in hot gas media
All members of the energetic balance of the plant have specific influence. According to the
available information on energetic balance of the plant in hot gas surroundings the following
equation can be written:
¦Q
Q s Q š Q tr Q vp
(3)
0.
Having extended the equation (3):
¦Q
ª § T1 · 4 § Ta · 4 º
H t C o «¨
¸ ¨
¸ » D t1 t a rw 105 w
¬« © 100 ¹ © 100 ¹ ¼»
0.
(4)
Here Ht the supposed degree of blackness of the investigated bodies (a plant or a weed destruction
equipment) system (DROBAVICIUS A. et all (1974)); T1, t1 the temperature for weed killing
equipment, K 0C; Ta , ta surface temperature of the plant organ K, 0C, w – the intensity of
transpiration kg/(m2s).
The equation (4) shows that surface of the plant gets the heat through radiation and convection.
Considering the convection as the main heat exchange element, total specific heat flow for a plant
(MILENSKIS N. et all (1968)) is as follows:
(5)
Qš QS (D K D sp )t1 t a ,
Here Dsp heat return through radiation coefficient, DK heat return through convection
coefficient.
If DK+Dsp=D1 (here D1 general heat return coefficient), then, (5) equation gets the following
expression:
D 1 t1 t a w r 105 .
(6)
A water evaporation heat in the investigated conditions is r = 2256 kJ/kg (DROBAVICIUS A. et all
(1974)). So, (r+105)|2361 kJ/kg. Then plant heat balance equations for high temperature air or
burning products surroundings take the following final expression:
D 1 t1 t a 2361 w.
(7)
The plant adapts itself to the environmental conditions. The »resistance« to unfavourable
positive energy balance is manifested by growing transpiration intensity. As grass flour production
experiments show, in high temperature drying chamber the temperature of grass mass, having
257
heated it or 15-25 min., increases only up to 50-64°C. This shows that having increased
transpiration, the plant uses surplus heat from environment, and, therefore, the tissues temperature
decreases. A weed experiences analogical conditions, when hot air or burning product high
temperature environment is used to kill it.
Plant tissue energy balance in humid water steam environment
Equation (8) describes all possible energy exchange in the plant. In case of plant tissue energy
balance in extreme condition, under the influence by condensating 100°C temperature humid steam,
some members of the balance can be rejected, as they have too little or no influence. Having this
analysis in consideration, plant energy balance in humid water steam environment can be expressed
by the following equations:
¦Q
r Q š r Q ta ,
F D 1 t1 t a Mc t ag t ap . .
(8)
(9)
They equations show, that under humid water steam influence (normal conditions =100°?), the
plant has no possibilities of physiological resistance to thermal influence of the steam. As it is
shown in (9) equation there are no physiological possibilities to reduce plant heat surplus, which
forms from condensating steam on plant organs surface. 100°C steam should influence surface
tissues of plant surface in a moment and kill them. This statement is corroborated by (9) equation,
which shows, that all heat received by the plant from environment (steam) goes to the increase of
plant tissues temperature.
Generalisation of findings
Plant energy balance in hot gas surrounding equation (3) and plant organ energy balance in
humid water steam environment equation (9) are used in modelling temperature field spreading in
plants tissues. Having solved differential equations temperature change in plant tissues under
different possible weed killing conditions is calculated. Calculation data shows the temperature
change in plant surface layer when heating with steam D 50000 W/(m2K) (continuous line) and
with water (dotted line), when w 0 D 30 W/(m2K) (Fig. 2). Theoretical calculation of unstable
thermal process (Fig. 2; curves 7, 8) says, that in high temperature gas surrounding is not good for
weed killing, however, it is researched and applied all over the world (BERTRAM A. (1996), HEGE
H. (1990), HOFFMANN M. (1989), ASCARD J. (1995). Temperature change in the weed stem
(diameter 3,1 mm) centre (Fig. 3; curve 2) is presented. During the time of the experiment hot air
stream temperature was about 350oC (3 Fig. 3 curve), environment temperature - 10,6oC. Curves in
Fig. 3 show little increase of plant stem temperature in centre (1,55 mm deep from surface) during
10 seconds. Sudden, in comparison with the experimental curve (Fig.3; curve 2), increase of
temperature in 1,5 mm depth from the surface, which is theoretically calculated (Fig. 2; curve 7),
can be explained by failing to take in to account the transpiration influence, as w=0. This has been
done to simplify the calculation. Naturally, it has influenced the calculation results, - in Fig. 2
curves 7 and 8 (dotted) are significantly lower and are slightly different from the curve of 20oC
environment air temperature.
Having heated with air (350oC, 10 s) slight changes on plant surface only from the stream flow
side are observed. Theoretical data shows (SIRVYDAS A. P. 1993) that high temperature gas stream
does not create effective thermal weed control equipment for organic agriculture.
Temperature change in the surface layer of a plant
258
(Fig. 2) shows that steam surrounding gain an advantage (curves 15) over air surrounding when
temperature is equal (curves 7, 8) during weed control. Theoretical and experimental data shows
that effective thermal weed control technology can be used only in water steam surroundings.
°C
100
1
2
80
3
60
4
40
20
8
6
5
7
0
0
2
4
6
10 s
8
Fig 2. Temperature change in the surface layer of a plant stem, when D(steam)=50 000 W/(m2. K)
(continuous lines) and D(air)=30W/(m2.K), at w=0, (dotted lines). When heating with water steam:
curve 1 - in the depth of 0,001 mm; 2 - in the depth of 0,01 mm; 3 - in the depth of 0,1 mm; 4 - in
the depth of 1 mm; 5 - in the depth of 1,5 mm; 6 - in the depth of 2 mm. When heating with air:
curve 7 - in the depth of 1,5 mm, 8 - in the depth of 0,1 mm
°C
400
350
300
3
250
200
150
100
2
50
1
0
0
2
4
6
8
10 s
Fig 3.Temperature change in the weed stem and environment. 1 curve surrounding air
temperature; 2 in the plant stem centre (of 3.1 mm diameter); 3 high temperature air stream
Steam is aimed to disturb biological functions of a weed plant only in a short strip of 2-5 mm width
and make a ring of injured tissues (Fig. 4). This method of plant injury can relatively be called a
thermal steam knife. Such thermal injury requires the creation of specific steam outflow canal,
which has inner cross section of the form similar to that of Laval canal. For this purpose
experimental equipment for weed control with water steam was created at the Lithuanian University
of Agriculture, tested and improved in 1999-2000. In 1999-2001 this equipment was used in the
first laboratory experiments and field trials in the Research station of the Lithuanian University of
Agriculture.
259
Fig. 4. Theoretical model and practical results of a plant injury ring by water steam
The boilers of 2,5-15 kW power working on electricity and gas were used in the production of
humid water steam. Steam of 100 0C temperature was directed to the plant zone. Localized thermal
injury of plant stem was used for weed killing.
In laboratory experiments barley and weeds were grown in pots filled with soil, and their
sensitivity at different age periods to steam was analyzed. One pot-variant width was 40x50 cm, six
repetitions. In field trial the experiment on weed control with water steam in barley crop was
carried out in the plots of 4,05 m2 in six repetitions. Weed samples were taken from 10 sites of
20x30 cm plots of every field. After drying the weeds were analyzed by species composition,
number and mass. Data was processed using ANOVA.
Results
Before the installation of field trials on weed control with water steam, barley sprouts sensitivity to
water steam was investigated under laboratory conditions. In the laboratory conditions barley was
sown every two days in seven terms. In one pot-replication one line of barley (variant) was sown in
randomized order on every second day. Thus, at the time of steaming every pot-replication had
barley sprouts of different size and seven sowing terms. In laboratory experiment steam for barley
sprouts steaming was used when the barley of the latest sowing (7th variant) started germinating and
their first leave was about to appear (Phase 9 according to ZADOKS (1974) scale). At that time in the
first variant the barley plants that had been sown 12 days earlier had two leaves (11th phase) and
were of 10-12 cm height, in the second variant – 8-10 cm height (11th phase), in the third – 6-8 cm
(11th phase), in the fourth – 3-6 cm (10th phase), etc. Having treated all barley sprouts in the
experiment with water steam of 100 0C temperature for 1,5 seconds no sudden or significant
changes were observed. However, some higher stems of sprouts leaned or even dropped in several
minutes. After 24 hours after steaming the injures became more significant, some leaves and even
plants dried off. The barley sprouts that had been sown earlier – the first, second and third variants
– were the most strongly influenced. In these variants the entire over-ground part of a plant was
injured. In later sown variants – fourth – sixth – barley plants were partially injured, only some of
them leaned down. In the seventh variant where the germination of barley was just starting no
significant injures caused by steam were observed.
After twelve days period after steaming the influence of steam on barley was established again
by calculating the percentage of barley that had survived steaming. The biggest number of barley
sprouts (91,0 %) survived in the seventh variant, where at the time of steaming barley was about to
germinate. In the sixth variant 87,1% survived, in the fifth one – 83,9%, in the fourth – 64,7%, in
the third – 40,2%, in the second – 20,0%, in the first – 3,53%. After the experiment the barley
sprouts were dried and weighed. Weight data was used in the calculation of barley dry mass
260
dependency on the age of barley sprouts, at the time of steaming (Fig. 5). The data showed the
barley sprouts to be sensitive to steaming, the bigger sprouts the more sensitive they were to water
steam of 100 0C temperature. Therefore, the equipment for weed control with water steam in barley
crop can be used for steaming of the entire crop only before barley germination. After barley
germination weeds in the spaces between rows can be steamed only having ensured barley plants
protection against negative influence of steam. This was done in the field trial.
Barley Sprouts mass
(mg / treatment)
600
500
400
300
200
100
0
0
2
4
6
8
10
12
14
Age of barley sprouts in days
y = 467,203·x-0,52419; R2 = 0,9234 t = 15,17
Fig. 5. Dependency of barley sprouts sensitivity to water steam on their age
Discussion
In field trial where the possibilities of steam use in weed control in barley crop were investigated
the barley was sown at bigger distances of (20 cm), which made the use of steaming equipment
possible. Special tin plates protecting barley plants against steam were added to the manual
equipment of steaming. In this trial the control variant was without steaming and 5 variants differed
in the time of steam application. (Fig. 6)
The most efficient weed mass reduction was observed after steaming in the phase of 2-3 leaves – in
the third variant, when barley was protected against steam. In this variant the weed mass was
reduced by 44 %. Two factors were active here: the steam effectively killed young weed sprouts
while the protected barley grew and smothered them. In this variant the barley yield was the biggest
one, by 6,67dt/ha higher than that in the control. In the other three variants barley was not protected
against negative influence of steam used in weed steaming, therefore, some of them were injured by
steam and thinned. Therefore, barley grain yield in those variants was significantly lower
(LAZAUSKAS P. (1993)).
261
The fact that in this experiment steam had stronger influence on perennial weeds than on annual
ones should be taken into consideration in the evaluation of steam influence on barley crop
weediness structure.
number of plants
5 0
n o n -u p ro o te d
u p ro o te d
4 0
3 0
2 0
1 0
0
0
0 .1
0 .2
p la n t d r y
Control
without
steaming
Clustering
phase,
barley
protected
2-3
leaves
phase,
barley
protected
2-3 leaves
phase,
only
spaces
between
rows
steamed,
barley not
protected
0 .3
m a s s (g )
2-3 leaves
phase,
entire area
steamed,
barley not
protected
Clustering
phase,
barley-not
protected
Fig. 6. Influence of different time of weed steaming on protected and not protected barley grain
yield, (dt/ha)– dark squares (LSD05=6.67) and on weed mass (g/m2 )
Conclusions
1. The analysis of thermal processes in a plant energy balance in specially created high temperature
environment with the purpose to destroy the plant thermally brings to the following statements:
x Energy balance members have different influence on plant organ surface temperature. The
plant organ surface temperature is mainly determined by convective heat exchange and plant
transpiration.
x When plant uses surplus heat that is received from high temperature gas surrounding,
transpiration increases, therefore, there is no sudden surface tissues temperature increase.
x Water steam surrounding immediately increases the temperature of plant surface tissues, it
has a destructive influence.
2. Field, laboratory and theoretical studies bring to the statement that in efficient thermal weed
control technology heat can be used only in water steam surrounding.
262
List of literature
ASCARD J. (1995) Thermal Weed control by Flaming //Dissertation Swedish University of
Agricultural Sciences, Department of Agricultural Engineering. Report 200.
BERTRAM A. (1996) Geräte und verfahrenstechnische Optimierung der thermischen Unkrautbekämfung. Weihenstephau, S. 196.
CESNA J., SIRVYDAS A., KERPAUSKAS P., VASINAUSKIENE R. (2000) Investigation of thermal weed
control in high-temperature media. Environmental Engineering-. VIII, Nr 1, 28-35.
DROBAVICIUS A. at all (1974) Bendroji šiluminơ technika Vilnius: Mintis, 470 p.
HEGE H. (1990) Thermische Unkrautbekämpfung // Gemüse, Nr 7. S. 344346.
HOFFMANN M. (1989) Abflammtechnik // KTBL, Schrift 331, S. 243.
INCROPERA F.P., DEWITT D.P. (1981) Fundamentals of heat transfer, New York, Chichester,
Brisbane, Toronto, Singapore, 819.
LAZAUSKAS P. (1993) The law of crops performance as a basis of weed control, -8 th. EWRS
Symposium, "Quanttitative approaches in weed and herbicide research and their application",Braunschweig,71-77.
MILENSKIS N. at all (1968) Bendroji šiluminơ technika. Kaunas, p. 106.
SIRVYDAS A. P. (1993) Termoenerginiai procesai augaluose ir jǐ aplinkoje. Kaunas: Akademija.
318 p.
SIRVYDAS A. P., CESNA, J (2000) Energy processes modeling in weed tissues and weed control.
Agricultural engineering, Research papers 32, Raudondvaris, P 53-72.
SIRVYDAS, A.P. (1993) Termoenergetiniai procesai augaluose ir jǐ aplinkoje. Kaunas-LZUA, 320.
ZADOKS J.C., CHANG T.T., KONZAK, C.F (1974) A decimal code for the growth stages of cereals.
Weed Research, Volume 14, Nr. 6., 415 – 421.
Methodology and research in physical and cultural weed control
263
264
Effect of plant dry mass on uprooting by intra-row weeders
1
D.A.G. Kurstjens1, G.D. Vermeulen2 & P.O. Bleeker3
Wageningen University, Soil Technology Group, P.O. Box 43, 6700 AA Wageningen, The
Netherlands. dirk.kurstjens@user.aenf.wau.nl
2
Institute of Agricultural and Environmental Engineering (IMAG), P.O. Box 43, 6700 AA
Wageningen, The Netherlands. g.d.vermeulen@imag.wag-ur.nl
3
Applied Plant Research (PPO), P.O. Box 430, 8200 AK, Lelystad, The Netherlands.
p.bleeker@ppo.dlo.nl
Introduction
The effectiveness of intra-row mechanical weed control depends on crop and weed growth
stages, machine adjustments and soil conditions. We aim to develop a set of field assessments to
quantify the performance of selective mechanical weeders such as weed harrows, torsion weeders
and finger weeders. This measurement protocol should allow analysis of plant, soil, weather and
machine effects and allow for better comparisons between sites and times. The method to quantify
the percentage uprooted plants as related to plant dry mass presented in this paper is a component of
this envisioned protocol.
Immediately after mechanical weeding, uprooted and non-uprooted plants were separately
collected from 5-cm wide intra-row zones. The total length of the excavated zone per plot ranged
from 2-10 m, depending on weed density. In the laboratory, collected plants were washed, separated
per species, dried for 24 hours at 105°C and then weighed individually. Based on sorted lists of
plant dry weight and uprooting status per species and implement, the relationships between plant
dry weight and %uprooting were plotted, with each point representing 9-31 plants.
Data were gathered from field experiments with torsion weeders, finger weeders and a spring
tine harrow on sandy and clay soil, at two subsequent treatment dates.
Results
The first mechanical weeding was generally more effective than a second pass 9-10 days later
(Fig. 1). This was partially related to the increased median dry weight of all weeds (sand 9/16:
0.003 g; sand 19/6: 0.017 g; clay 24/5: 0.025 g; clay 2/6: 0.070 g). In most situations, the variation
in plant dry mass within species was so large (variation coefficients ranging from 1.2 to 2.1) that
uprooting effects at different sites and times can only be compared sensibly using plants of
approximately the same size (Fig. 2).
When taking plant mass into account, torsion weeders were more effective than the weed
harrow or finger weeders, except on clay soil (Fig. 3). On sandy soil, the first torsion weeding was
more effective than the second with Poa annua (Fig. 3A, B), whereas points of Solanum nigrum
and Stellaria media were approximately on the same curve (Fig. 3C, E).
Linear relationships between logit-transformed uprooting percentages and plant dry mass were
fitted to individual plant data, using IRREML in Genstat 5. Maximum weed uprooting percentages
(at zero plant weight) below 100% may indicate a less intense or an irregular disturbance of the
intra-row topsoil. The plant mass at which a certain percentage is uprooted could be used to
265
compare effects of site characteristics or implement adjustments. The slope of the curve may be
related to the selective uprooting ability of the weeders.
sand 9-6
clay 24-5
% uprooted weeds
100
sand 19-6
clay 2-6
80
60
40
20
0
torsion weeder
Figure 1.
finger weeder
weed harrow
The uprooting effect of mechanical weeders on different soil types and treatment dates.
Means of all species together with mean standard errors.
number of plants
50
non-uprooted
uprooted
40
30
20
10
0
0
0.1
0.2
0.3
plant dry mass (g)
Figure 2.
Example frequency distribution of Solanum nigrum plant dry mass collected directly
after finger weeding and weed harrowing on sandy soil at 19/6. The corresponding
relationship between plant dry mass and uprooting is depicted in Fig. 3D.
Discussion
As the sensitivity of weeds to uprooting varied considerably within populations present in the
field, it is sensible to take account of this variation when comparing mechanical weed control
effectiveness between sites and times. If soil conditions and machine adjustments are adequately
recorded as well, regression models that include individual plant dry mass may be used to analyse
these effects.
B 100
Poa annua, sand 9/6
torsion weeder
finger weeder
weed harrow
80
percentage uprooted
percentage uprooted
A 100
266
60
40
20
0
60
40
20
Solanum nigrum,
torsion weeder
80
0
clay 24/5
sand 9/6
sand 19/6
60
40
20
D 100
0
0.01
0.02
plant dry mass (g)
Solanum nigrum,
finger weeder + weed harrow
clay 24/5
80
sand 19/6
60
40
20
0
0.05
0.1
plant dry mass (g)
Stellaria media,
torsion weeder
80
0
0.15
F 100
clay 24/5
sand 9/6
sand 19/6
percentage uprooted
0
percentage uprooted
80
0.01
0.02
plant dry mass (g)
percentage uprooted
percentage uprooted
C 100
60
40
20
0
0.05
0.1
plant dry mass (g)
0.15
Stellaria media,
finger weeder + weed harrow
clay 24/5
sand 19/6
80
60
40
20
0
0
Figure 3.
torsion weeder
other implements
0
0
E 100
Poa annua, sand 19/6
0.05
0.1
plant dry mass (g)
0.15
0
0.05
0.1
plant dry mass (g)
0.15
Relationships between plant dry mass and the percentage uprooted weeds per species.
This method appears suitable to assess uprooting if plants are not moved to or from the row.
This precondition probably does not apply with finger weeders, so that weeds should also be
counted before treatment at the same spot. Principally, this method could be applied to covering
damage as well, by collecting plants in four categories (before excavation: visible uprooted, visible
not uprooted; during excavation of loose soil: covered uprooted, covered not uprooted). Such
measurements combined with a method to assess plant recovery from uprooting and covering
damage and new weed emergence a few days after treatment could help explain the variability in
mechanical weeding effectiveness.
267
Evaluation of Physical Weeders
J. Meyer 1), N. Laun2), B. Lenski2)
1) Technische Universität München,
Department für Biogene Rohstoffe und Technologie der Landnutzung,
Fachgebiet Technik im Gartenbau, Am Staudengarten 2, 85354 Freising-Weihenstephan
e-mail: Meyer@tec.agrar.tu-muenchen.de
2) Lehr – und Versuchsbetrieb, Queckbrunnerhof, Dannstadterstraße 91, 67105 Schifferstadt;
e-mail: NLaun.slfa-nw@agrarinfo.rlp.de
e-mail: Blenski.slfa-nw@agrarinfo.rlp.de
Abstract
Weed control is one of the most labour consuming tasks in organic farming. Therefore, farmers
have a tremendous interest in an effective mechanisation of weed control.
The “Weihenstephaner Trennhacke (Split hoe)” is a modified mechanical hoe. Results demonstrated
that the Split hoe improved weed control compared to a common mechanical hoe, especially under
all conditions that favour a renewed growth of the weeds (wet / crusted soil, big weeds).
The improved weed burner “Weihenstephaner Streifenabflammgerät (strip flamer)“ is characterised
by a slim cover on each single row which keeps the hot air close to the ground. This allows a higher
working speed and reduces the gas consumption.
In contrast to other vegetables, onions can be flamed past emergence. The available time for
flaming could be influenced by a deeper seed placement and the choice of a later ripening variety.
Plant damages were mainly due to the growth stage. Onion plants compensated even the complete
loss of the cotyledon leaf. In the first true leaf stage crop losses were observed which increased with
energy input.
Two innovative implements (Split hoe, Strip flamer) for weed control in organic grown vegetables
were tested in a two years period under field conditions in a region (Southwest of Germany) which
is characterised by sandy loamy soils (organic matter 2%, pH 7.5), an annual precipitation of about
600 mm. A detailed description of the machinery is given by A. Bertram (1996). Trials about
weeding effects were carried out in spring sown onions in randomised complete block design
arrangements with 4 repeats per treatment and minimum plot sizes of 12 x 1.88 m. Plant density
was about 30 to 40 plants per m of row with 4 rows per bed.
268
Fig. 1: Weihenstephaner Trennhacke (Split hoe)
The “Strip flamer“ was characterised by temperature measurements conducted with the
complete implement as used in the field. For most accurate results these tests were run on a paved
ground to exclude any side effects, e.g. differences in soil moisture and in the ground surface.
The tests were aimed on the comparison of three burners to obtain their specific temperature
features, mainly the maximum temperatures, and to specify the influence of soil particles on these
temperatures. Measurements were made with four thermocouples type k. Sensors were connected to
a PC and data were logged by using QuickLog PC provided by Strawberry Tree Inc. The system
was adjusted to store five temperature measurements per second.
Results and Discussion
Strip flamer
Temperatures under the covers varied strongly between single burners of the same
implement, which may result in varying quality of weed control. Although the burners were bought
from a well known dealer, it seems to be necessary to carry out some tests about the energy output
of each single burner. For technical improvements the big differences between burners should be
reduced (Tab. 1).
Maximum temperatures of single burners (3 km/h)
burner 2
burner 3
Temperature (°C)
72
55
Standard deviation
2.9
4.0
Min. / max. (°C)
69 / 76
51 / 61
269
Tab. 1:
burner 4
60
3.7
57 / 66
The influence of the driving velocity on the temperatures is shown in Tab. 2.
Tab. 2: Influence of the driving velocity on maximum temperature
2 km/h
4 km/h
mean Temperature (°C)
65
49
Standard deviation
13.9
7.8
Min. / max. (°C)
43 / 77
34 / 56
6 km/h
47
4
42 / 49
At higher driving velocities the uniformity of the temperature under the cover seems to
improve. Nevertheless the temperatures were higher in the middle of the tunnel then on the sides
(49°C and 42°C). Therefore the burners should be placed exactly over the middle of the row to
achieve good results.
Effect of flaming on the crop
Most vegetables, except onions, can only be flamed before emergence, which limits the
flaming period strongly. It could be demonstrated that culture practices can extend the available
time for flaming in onions. Emergence could be delayed for 4 to 6 days by the depth of sowing (3
cm compared to 1 cm) and 3 to 4 days depending on the cultivar. Early ripeness of cultivars was
linked with early emergence. When flamed post emerging, the damage of onions depended on the
growth stage and the driving speed during flaming. Even the complete loss of the cotyledon leaf
could be compensated in the further development of the plants. However, when the first true leaf
was affected, plant losses were observed.
Fig. 2:
Effect of flaming date on plant losses in onions
(left: flaming 11.04.00 in the hook stage with the first true leaf visible (in parts) , right:
flaming 6.04.00 early hook stage)
270
The losses increased with energy input (30 remaining plants/m without flaming, 26 plants/m
flaming with 20 kg gas/ha (5.4 km/h); 22 plants/m with 40 kg gas/ha (2.7km/h). Under field
conditions a five day delayed flaming (early/late pre-emergence) resulted in a 27 % loss (at 4 km/h)
of plants (Fig. 2).
Effect of soil surface on flaming results:
The success of weed control increased with a finer surface preparation of the seedbed. The
implements used for the first step of soil preparation (rotary hoe / rotary harrow) had only a slight
influence on the final surface of the soil. The roughness of the soil surface decreased depending on
intensity of final rolling (Fig. 3).
100
rotary hoe
90
rotary harrow
80
70
60
50
40
30
20
10
0
Cambridge roller
Fig. 3:
barrow roller
not rolled
Effect of the soil surface on the preparation efficacy of flaming
It could be demonstrated, that soil clods act as a barrier for the spread of temperature This
temperatures directly behind clods are clearly reduced (Tab. 3).
Tab. 3: Influence of soil particles on maximum temperatures (v = 2 km/h)
before the clod
1 cm behind the clod 5 cm behind the clod
Temperature (°C)
106
84
93
Standard deviation
10.65
8.78
6.49
MIN / MAX (°C)
95 / 117
76 / 93
87 /102
Results “Split hoe“
Results show that the “Split hoe” improved weed control compared to a common mechanical hoe.
The rotating tines remove soil from the roots. Using the improved hoe, the efficiency, measured as
percentage of damaged weeds, reached 96 to 99 % compared to 30 to 95 % with the standard hoe
(Fig. 4). Advantages of the “Split hoe” were strongly demonstrated under all conditions that favour
a renewed growth of the weeds. These were: wet or crusty soils, well rooted and big weeds, and the
presence of grasses. This lead, very often, to a longer period for successful weed control. Efficacy
was increased significantly not only on crusted soils, but on also lighter, well structured soils. Even
271
weeds up to 60 cm height could be controlled as they remained to the surface and were not covered
with soil. The renewed growth of weeds was higher using a standard hoe, especially for the grass
weeds.
80
"Trennhacke"
70
standard hoe
60
50
40
30
20
10
0
grass weeds
Fig. 4:
broad leaf weeds
Influence of standard hoe and “Split hoe” on efficacy of weed control
References
A. BERTRAM (1996), Geräte und verfahrenstechnische Optimierung der thermischen
Unkrautbekämpfung, PhD thesis. TUM-Weihenstephan, Freising
H. WEBER (1997), Geräte und verfahrenstechnische Optimierung der mechanischen
Unkrautregulierung in Beetkulturen, PhD thesis. TUM-Weihenstephan, Freising
272
Effect of cutting height on weed regrowth
S. Baerveldt1 and J. Ascard2
1. Swedish University of Agricultural Sciences, Department of Agricultural Engineering, P.O. Box
66, S-230 53 Alnarp, Sweden
2. Swedish University of Agricultural Sciences, Department of Crop Science, P.O. Box 44, S-230 53
Alnarp, Sweden)
Abstract
Matricaria inodora L., Chenopodium album L. and Poa annua L., grown under controlled
conditions, were cut below or above the lowest growing point at various stages of development. No
plants survived when they were cut under the lowest growing point, i.e. just below the cotyledons for
M. inodora and C. album and just below the soil surface for P. annua. When the plants were cut off
above the lowest growing point, most survived but there was significant reduction in fresh weight for
all species and development stages. Thus, the cutting height required for effective weed control
depends on the position of the cotyledons and growing point. The regrowth of M. inodora was
slower the older the plants were at cutting. For P. annua the situation was the opposite with faster
regrowth from older plants.
Introduction
There is renewed interest in mechanical weed control as an alternative or complement to chemical
methods. The traditional techniques for mechanical weed control need to be improved to make them
more efficient. More basic knowledge is needed about how much and in what way a plant must be
damaged in order to be killed. This knowledge may become useful for developing more efficient
technical equipment for mechanical weed control.
Most of the mechanical methods used today for example harrowing, hoeing and brushing
cultivate the soil and control weeds by a combination of pulling and soil covering (Habel 1954, Kees
1962, Koch 1964, Rasmussen 1990, Rydberg 1993). Another way of controlling annual weeds is to
cut them off. The soil does not then have to be cultivated and this can give some advantages; it can
decrease soil erosion on easily eroded soils and soil moisture has less influence on the time of
treatment (Estler & Nawroth 1995).
When weeds are cut, they lose a major part of their photosyntetically active biomass which gives
the crop plants a competitive advantage. The distance between the soil surface and the cutting site is
important. Jones et al. (1995) found that cutting at the soil surface was more effective than cutting 1
cm above or 1 cm below the soil surface for Stellaria media (L.) Vill., Papaver rhoeas L., Poa
annua L. and Poa trivialis L.. When the upright growing Chenopodium album L. was cut 2 cm
above the soil surface almost all plants were killed, but if the plants were cut off 5 cm above the soil
surface, the regrowth was high (Estler & Nawroth 1995).
Weed sensitivity to cutting depends also on the species. Plants of P. rhoeas, which is rosette
forming, were more sensitive to cutting at the soil surface than plants of S. media, which has
prostrate growth, at the same stage of development (Jones et al. 1995). Estler & Nawroth (1996)
found that the regrowth of the dicotyledonus C. album after cutting was less than the regrowth of
the monocotyledonus Echinochlos crus-galli (L.) cut at the same distance from the soil surface.
273
These earlier investigations on weed control by cutting mainly studied the effect of cutting at a
specified height above ground level. There was no evaluation of the position of the cut in relation to
cotyledons and vegetative growth points.
The aim of this study was to investigate the regrowth of three weed species of different growth
habits, after cutting the plants above or below the lowest growing point at various stages of
development, and the implications for weed control.
Experiments
Three species of weed with different growth habits were chosen ; P. annua has prostrate growth, C.
album is upright growing and Matricaria inodora (L.) is rosette forming. The plants were grown in
13 cm x 18 cm pots filled with limed and lightly fertilized peat soil. C. album and M. inodora were
sown on moist filter paper, and six germinated seedlings were then transplanted into each pot. P.
annua was sown directly into the pots and the number of seedlings was thinned to 6 plants per pot
before treatment.
The plants were grown in a climate chamber, where the climate was adjusted to resemble the
average climatic conditions of the 15th of May in Southern Sweden. This time of the year was
chosen as it is a normal time for early weed control. The day length was 16 hours, with the maximum
light intensity of 550 Pmol m-2 s-1 for 10 hours. Relative humidity was 80% during the night and 56
% in the middle of the day. Minimum and maximum temperatures were 7.5 °C and 14.5 °C,
respectively. All climatic factors were changed linearly over time. In order to regulate water supply,
the pots were placed on a fibre cloth and sub-irrigated, the soil was kept moist throughout the
experimental period.
The three species they were cut in relation to their lowest growing point, therefore they were cut
at different heights above the soil surface. P. annua has the growing point just at the soil surface and
were cut just below the soil surface when they had 2 leaves or just above soil surface when they had
1, 2 or 5 leaves. C. album and M. inodora have the lowest growing point at the cotyledons and these
plants were cut just under the cotyledons when they had 2 true leaves or just above the cotyledons
when they had 2, 4 or 6 true leaves. Control plants, grown at the same conditions as the cut plants,
were included in each experiment.
The experimental layout was a completely randomized design with four replicates, each
consisting of a single pot with 6 plants. About two weeks after treatment, the above-ground fresh
weight was recorded.
An additional experiment was carried out with M. inodora. In order to study the regrowth more
carefully, the fresh weight was measured just after cutting and 1, 2 and 3 weeks after cutting. The
plants were cut just above the cotyledons when they had 2, 4 or 6 true leaves. There were 12 pots
with 6 plants per pot for each developmental stage, and the fresh weight was recorded for the plants
in 4 pots at each assessment time. Experimental conditions were otherwise similar to the first
experiment.
Statistical analysis
The fresh weight data were analyzed by One Way Analysis of Variance. No transformation was
needed according to Bartlett's Test for homogeneity in variance. A two sample test was used to
compare cut plants with control plants.
To describe the regrowth of M. inodora during three weeks after cutting a growth model was
used. The chosen model was the following three-parameter logistic model (Ratkowsky, 1990;
Streibig et al., 1993):
274
Dk
k
(1)
(1 a / x ) b
Parameter D describes the upper asymptote, b describes the slope of the curve around a.
Parameter a is the number of days after sowing that gives the response (D-k)/2. The constant k was
set to the mean of the fresh weight of the plants just after cutting. X is days after seeding and Y is
g/plant.
Curve fitting was performed by non-linear regression using the Least Squares method
(Anonymous, 1991). To stabilize the variance, a power transformation (ln y) was used. The
transformed data were analyzed by the Transform-Both-Sides technique (Snee, 1986; Streibig et al.,
1993).
Y
Results
All plants died in all experiments when they were cut just under the lowest growing point, i.e. just
below the soil surface for P. annua and between the soil surface and the cotyledons for C. album and
M. inodora. When the plants were cut above the lowest growing point, most plants survived but
there was a significant (P<0.05) reduction in fresh weight compared to the untreated control.
Fresh weight per plant (g)
Poa annua
When plants of P. annua were cut just above the soil surface, 41% of the 1-leaf plants, 21% of the 2
leaf plants and 18% of the 6 leaf plants were killed. In other words, more plants were killed when
they were cut at earlier stages. The plant weights at assessment were significantly (P<0.05) lower
when plants were cut at a younger rather than an older stage (Fig. 1). The relative reduction in fresh
weight compared with an untreated control was similar and significant for all stages of development.
Cut plants
Control
0,3
0,3
0,2
0,2
0,1
0,1
0,0
(94%)
(91%)
(93%)
11
32
55
0,0
Number of leaves at treatment
Figure 1. Effect of cutting on Poa annua plants two weeks after cutting just above the lowest
growing point. The numbers in parenthesis shows the relative reduction in fresh weight of cut plants
compared with control plants. Vertical bars indicate standard error of the mean.
275
Chenopodium album
All plants survived when they were cut between the cotyledons and the first true leaves. The fresh
weight of the plants cut at the 2 leaf stage was significantly lower (P<0.05) than the fresh weight of
plants cut at the 6 leaf stage (Fig. 2). The relative fresh weight reduction was slightly higher when
the plants were cut at later growth stages.
Cut plants
Control
1,6
1,6
1,2
1,2
0,8
0,8
0,4
0,0
(79%)
2
(87%)
(83%)
4
6
0,4
0,0
Number of true leaves at treatment
Figure 2. Effect of cutting on Chenopodium album plants two weeks after cutting just above the
lowest growing point. The numbers in parenthesis shows the relative reduction in fresh weight of cut
plants compared with control plants. Vertical bars indicate standard error of the mean.
Matricaria inodora
All plants survived when they were cut between the cotyledons and the first true leaves. The fresh
weight of the plants two weeks after cutting was not significantly different for any of the three stages
of development at which cutting back occurred (Fig. 3). However, the relative reduction in fresh
weight was considerably higher when the plants were cut at a more advanced stage of growth.
276
Cut plants
Control
1,2
1,2
0,8
0,4
0,0
0,8
(32%)
2
(78%)
(75%)
4
6
0,4
0,0
Number of true leaves at treatment
Figure 3. Effect of cutting on Matricaria inodora plants two weeks after cutting just above the
lowest growing point. The numbers in parenthesis shows the relative reduction in fresh weight of cut
plants compared with control plants. Vertical bars indicate standard error of the mean.
When the regrowth of M. inodora was measured 1, 2 and 3 weeks after cutting, the logistic model
(1) gave a good description of the regrowth capacity (Fig. 4 and Table 1). The estimated parameters
and the standard error show that the model seems to be reasonable although the model is relatively
complicated and the curves were fitted using only four experimental points (with four replicates in
each point). The slope of the curve around a, parameter b, describes the regrowth capacity of the
plants after cutting at different stages of development and the growth capacity of untreated plants.
Plants cut when they had 2 leaves showed a high regrowth capacity. When the plants had 6 leaves at
cutting the curve was quite flat, indicating poor regrowth capacity.
10
1,2
20
30
277
40
50
Control
Cut at 2-leaf stage
Cut at 4-leaf stage
Cut at 6 leaf stage
1,2
0,8
0,8
0,4
0,4
0,0
0,0
10
20
30
40
50
Days after seeding
Figure 4. Effect of cutting just above the lowest growing point on Matricaria inodora at different
stages of development. At the 2- 4- and 6-leaf stage, plants were cut 13, 20 and 27 days respectively
after seeding.
Table 1. Parameter estimates of regression (model 1) for plant fresh weight, data after cutting plants
of Matricaria inodora at different stage of development. Standard errors (SE) are given in
parentheses.
Treatment
No. of leaves at
treatment
Control
cut
cut
cut
2
4
6
Upper limit
D (SE)
g/plant
1.42 (0.16)
1.21 (0.33)
0.34 (0.02)
0.34 (0.04)
Slope
b (SE)
a (SE)
days after seeding
5.6 (0.59)
6.41 (0.57)
8.08 (0.61)
11.8 (2.94)
33.1(1.77)
34.6 (3.62)
32.4 (1.07)
39.9 (2.11)
Discussion
As long as the plants are cut below the lowest growing point, they will be killed by the treatment. P.
annua and M. inodora have their lowest growing point near the soil surface while C. album has its
lowest growing point about 1-2 cm above the soil surface. Therefore, P. annua needed to be cut off
just under and M. inodora just above the soil surface to kill all the plants, while C. album could be
cut off 1-2 cm above the soil surface. Earlier investigations only described at what height above the
soil surface at which plants were cut (Estler & Nawroth 1995, Jones et al. 1995), but the results
largely agree with these studies.
278
When the plants were cut just above the lowest growing point the only thing left of the plants of
C. album or M. inodora were the cotyledons and a stem. Two weeks after cutting there was only a
small difference in regrowth between plants of either C. album or M. inodora treated at different leaf
stages. However the relative reduction in fresh weight compared with the untreated control was
higher for older plants, which is probably because more biomass was cut off at the later stages. La
Hovary et al. (1995) also found that the reduction in biomass was greater when plants of several
dicotyledonous species were cut at the 6-leaf stage than when they were cut at the 3 leaf stage.
When the regrowth of M. inodora was studied during three weeks after cutting it was obvious
that the regrowth capacity was lower when the plants were cut at older stages of development. One
reason for this might be that the cotyledons had regenerated more on the older plants and, as the only
green part left after cutting was the cotyledons, the assimilation capacity of the older plants was low.
When plants of P. annua was cut above the lowest growing point the only part left was about 1
mm high stems. In contrast to C. album and M. inodora, plants of P. annua had significantly higher
fresh weight at assessment when cut at later growth stages. The older plants of P. annua seemed to
have a higher regrowth capacity than the younger. This is probably due to the fact that grasses are
continually forming new tillers at the soil surface, which enhances regrowth. Some plants of P.
annua were killed although cut above the growing point, probably because the growing point of
these plants was damaged, or because too large a portion of the biomass was removed.
Conclusions
The results indicate that cutting may become a useful method for control of dicotyledonous uprightgrowing weed species such as C. album. Grass weeds and rosette-forming weed species, however,
are probably more easily controlled by shallow tillage than by cutting, since these plants have to be
cut at or below the soil surface. The technique of weed cutting may become especially useful in the
production of root crops such as carrots with a slow initial growth. In early spring, many weeds
commonly grow taller than the carrot seedlings, which makes it possible to cut upright growing
weeds close to the ground while saving the carrots. In fact, this method is practised today by some
organic carrot growers, who are able to reduce the need for hand weeding by early weed cutting
when the crop plants are small. Further research is needed to develop the method further in different
crops.
Acknowledgements
The research was supported by Swedish Farmers Foundation for Agricultural Research. We are
grateful for valuable comments on the manuscript from Jan Eric Englund, Ann-Marie DockGustavsson and Bengt Lundegårdh.
279
References
ANONYMOUS (1991) Statgraphics statistical graphics system. Reference manual. STSC, inc.,
Rockville, Maryland, USA.
ESTLER, M. & NAWROTH, P. (1995). Mechanische Unkrautregulierung ohne Eingriff in das
Bodengefuge. Landtechnik, 3, 142-143.
ESTLER, M. & NAWROTH, P. (1996). Mechanische Unkrautregulierung ohne Eingriff in das
Bodengefüge
- Gerätetechnik, Prüfstandsversuche, Ergebnisse - Zeitschrift für
Pflanzenkrankheiten und Pflantzenschutz, Special Issue XV, 423-430.
HABEL, W. (1954). Über die Wirkungsweise der Eggen gegen Samenunkräuter sowie die
Empfindlichkeit der Unkrautarten und ihrer Alterstadien gegen den Eggenvorgang. PhD
thesis, Landwirtschaftlichen Hochschule Hohenheim.
JONES, P.A., BLAIR, A. M. & ORSON, J. H. (1995). The effect of different types of physical
damage to four weed species. In Proceedings Brighton Crop Protection Conference - Weeds,
653-658. Brighton.
KEES, H.
(1962). Untersuchungen zur Unkrautbekämpfung durch Netzegge und
Stoppelbearbeitungsmassnahmen unter besonder Berücksichtigung des leichten Bodens. PhD
thesis, Landwirtschaftlichen Hochschule Hohenheim.
KOCH, W. (1964) Unkrautbekämpfung durch Eggen, Hacken und Meisseln in Getreide. 1.
Wirkungsweise und Einsatzzeitpunkt von Egge, Hacke und Bodenmeissel. Zeitschrift für
Acker- und Pflanzenbau, 120, 369-382.
LA HOVARY, C., LEROUX, G.D. & LAGUE, C. (1995). Determination of optimum method and
timing for mechanical weed control in corn. Weed Science Society of America, Abstracts, 35,
139.
RATKOWSKY, D.A. (1990). Handbook of Nonlinear Regression Models. Marcel Dekker; New
York - Basel.
RASMUSSEN, J. (1990). Selectivity. An important parameter on establishing the optimum
harrowing technique for weed control in growing cereals. In. Proceedings of the EWRS
Symposium 1990. Integrated Weed Management in Cereals, 197-204.
RYDBERG, T. (1993). Weed harrowing - Driving speed at different stages of development. Swedish
Journal of Agricultural Science, 23, 107-113.
SNEE, R.D. (1986). An alternative approach to fitting models when re-expression of the response is
useful. Journal of Quality Technology, 18, 211-225.
STREIBIG, J.C., RUDEMO, M. & JENSEN, J.E. (1993). Dose-response curves and statistical
models. In: Herbicide Bioassay (J.C. Streibig & P. Kudsk eds), pp. 29-55. CRC Press; Boca
Raton, Florida.
280
Yield effect of distance between plants and cutting of weeds
T. Heisel, C. Andreasen1 & S. Christensen2
Department of Crop Protection, Danish Institute of Agricultural Sciences,
DK-4200 Slagelse, Denmark, Torben.Heisel@agrsci.dk, 1Department of Agricultural Sciences, The Royal Veterinary
and Agricultural University, Højbakkegaard Allé 17, DK-2630 Taastrup, Denmark and 2Department of Agricultural
Engineering, Danish Institute of Agricultural Sciences, DK-8700 Horsens, Denmark.
Abstract
A sugar beet field experiment was conducted in 1999 and 2000 to measure beet yield when Sinapis
arvensis L. or Lolium perenne L were growing 2, 4 or 8 cm from the beet. The weed was cut once
in the growing season (late May, mid June or early July) and the number of neighbour beets to
every single beet were registered. Increasing distance from 2 to 8 cm between beet and weed
increased the beet yield significantly in average with 20%, regardless of weed species. The beet
yield increased significantly when cutting of the weed was postponed to mid June and the total
weed biomass increased significantly when cutting was postponed to the period between mid June
and early July. The number of neighbours described an approximate linear yield decline of the
single beet.
Introduction
Hoeing uproots or covers the weeds by soil and thereby delays or impedes weed growth. A
disadvantage of hoeing is that the disturbance of the soil often initiates new weed seed germination
and emergence. Cutting a weed at ground level can be an alternative method where soil disturbance
is reduced (Jones & Blair, 1996). Dicotyledons can be killed, whereas monocotyledons can be
reduced in size and their growth may be delayed. Different mechanical devices to cut weeds
(Nawroth & Estler, 1996) and a new and potentially energy-efficient and precise CO2 laser method
have been presented (Heisel et al., 2001). Hoeing is usually done several times during the growing
season in organic sugar beets starting as early as possible to optimise the weed control. The optimal
time for controlling the weed by cutting might be later in the season, because the plants may be
easier to find and cut, when they have a certain size and because the critical period for weed control
might be affected. Hence, there is a need for investigating how the beet yield is affected if weeds
are cut later in the season.
The yield suppressing ability of the weed is highly dependent on the distance between a crop
plant and a weed (Weiner, 1982; Frank, 1990; Pike et al., 1990). Usually the competition between
plants increases when the distance decreases. However, the ability to cut a weed without damaging
the crop decreases with decreasing distance. Interactions between a cut weed and the distance
between weed and beet should be enlightened because the beet might be able to compete better with
a cut weed close to itself than to a cut weed further away.
Our objective was to investigate yield response of sugar beet to transplanted Lolium perenne L.
or Sinapis arvensis L. with respect to the distance between beet and weed and an aboveground weed
cutting at various growth stages.
281
Establishment and treatment dates for the complete trial are summarised in Table 1. One weed
plant per beet plant was used and the planting distance between weed and sugar beet plants was
chosen beforehand to be 2, 4, or 8 cm. Two competitive weed species, the monocotyledonous
Lolium perenne L. and the dicotyledonous Sinapis arvensis L., were chosen (Sarpe & Torge, 1980).
The species were transplanted in a growing sugar beet crop in order to obtain the chosen distances.
The growth and transplantation of the weed plants were synchronised to the crop establishment in
order to obtain crop weed competition similar to natural weed seedlings. The weeds were cut 2 cm
aboveground twice in 1999 and three times in 2000.
Table 1. Establishment/treatment dates and number of data points (n) of the various types.
Action
Seeding in trays
B. vulgaris sowing
Weed
transplantation
CUTTIME 0
CUTTIME 1
CUTTIME 2
CUTTIME 3
Weed harvesting
Single beet harvest
1999
2000
S. arvensis
L. perenne
S. arvensis
L. perenne
27 April
21 April
17 April
14 April
21 April
17 April
19 May
10 May
(n = 142)
(n = 142)
(n = 319)
(n = 319)
No cutting
6 June ~ 515 degree days
29 May ~ 538 degree days
3 July ~ 1027 degree days
6 August
20 October
25 September
26 – 29 October
13 – 15 November
(n = 284)
(n = 638)
Growing conditions and general design
S. arvensis and L. perenne were seeded in speedling trays and grown on watered cloth in an
outdoor voliere. The plant density in the trays was continuously thinned to one plant per tray hole.
One hectare was sown with sugar beets (cv. Marathon). The row distance was 50 cm and the seed
distance 18 cm. The experiment was a completely randomised block design with 56 plots of 2.5 m x
10 m in 1999 and with 80 plots of 2.5 m x 5 m in 2000. The plots were laid out in a northeast –
southwest direction in 1999, and in the north – south direction in 2000. Each plot consisted of one
combination of the factors DISTANCE from beet to weed (2, 4, or 8 cm), two and three weed
cuttings in 1999 and 2000 (CUTTIME) and the two weed species (SPECIES). The combinations
were replicated three times (REPL) in the block design.
Weeds were transplanted in the field with one weed plant per third beet plant (the competing
beet plant) in two rows. The second and fourth rows were chosen out of five. Weeds were
transplanted on the same side of the sugar beet in all plots (southwest in 1999, south in 2000). The
number of competing beet plants were 284 in 1999 and 638 in 2000. Naturally occurring weeds
were removed by hoeing, flaming, brush weeding or hand hoeing in 1999 and by pretransplantation spraying, hoeing, flaming or hand hoeing in 2000.
After approximately 520, 730 or 1030 daily degree days (CUTTIME) (corresponding to late
May, mid June or early July) weeds were cut with a pair of scissors approximately 2 cm from the
soil surface enabling both weed species to be able to re-grow. All non-controlled plants and regrown plants were harvested 2 cm from the soil surface when the growth stopped (see Table 1) and
the final weed dry weights (WEEDDW) were measured after 24 hours drying at 90°C. The
competing beet plants were harvested individually and the fresh weight (BEETFW) was measured
after cleaning. Neighbour beets were defined as the beets encircling the competing beet. The
282
number of neighbour beets (NEIGHB) in a 36 cm * 100 cm rectangle with the competing beet in the
centre was measured to enable an analysis of the effect of missing beets plants.
Statistical analyses
We wanted to test which factors had a significant effect on the beet fresh weight (BEETFW). A
general linear model with mixed effects and maximum likelihood estimation (Henderson, 1982;
Weisberg, 1985) was used to describe the variation in fresh weight of the single beet (BEETFW).
The plot number (PLOTNO) was included as random effect whereas the rest were included as fixed
effects. A square root transformation was used to stabilise the variance. The full model for the
complete data set (n = 922) were in a simplified form:
BEETFW = YEAR + REPL + PLOTNO + DISTANCE + SPECIES +
CUTTIME + NEIGHB + error
(1)
The errors and the effects of PLOTNO were expected to be normally distributed with a mean
value of zero and variation V2. YEAR, REPL, SPECIES and CUTTIME were analysed as class
variables whereas the rest were analysed as continuos variables. The model was analysed with all
two-way interactions included and hereafter reduced by eliminating non-significant (P < 0.05)
factor interactions and factors one at a time. Simultaneously the new reduced model was tested
against the parent model using twice the difference between the calculated values for the logarithm
to the likelihood (–2LogL) for the two models. The calculated difference is approximately Chi2distributed with the difference in degrees of freedom between the two models as degrees of
freedom.
Statistical analyses were performed in the software package SAS™ 8 (SAS, 2000). Regression
in Fig. 4 was performed with Microsoft® Excel™ weighted by numbers of samples.
The growing conditions were different in the two years. In 1999 the spring was cooler and the
summer warmer than in 2000. Furthermore, the autumn was extremely dry in 1999, all together
resulting in smaller beets (BEETFW) in 1999.
After successive reducing model 1 until it only consisted of significant factors we ended up
with model 2:
BEETFW = YEAR + DISTANCE + CUTTIME + NEIGHB + error
(2)
F-test for significance, estimate and standard error of estimate for each factor is shown in Table
2. There was a significant difference in the beet yield between the years mainly due to site and
climatic conditions.
The effect of weed species decreased linearly within the distance 2 to 8 cm from the sugar beets
in both years (Fig. 1 - note that Figs. 1, 2 and 4 were transformed back in scale). The sugar beet
yield with weeds at 2 cm distance was approximately 20% lower compared to weeds at 8 cm
distance from the beet plants. Similar results were presented with different distances between
Datura stramonium L and Xanthium strumarium L. on Glycine max L. (Pike et al., 1990). A linear
approximation showed a high correlation coefficient of G. max yield and increasing distance to the
283
two weed species. Similarly, the distance factor was found significant in describing annual plant
growth rate of Pinus rigida L. and intra-specific competition from neighbour trees (Weiner, 1984).
Table 2. Final model (2) on the total data set with 908 degrees of freedom for error after successive
reductions of model 1 with F-test for significance, estimate, estimate unit and standard
error of estimate (SE).
Effect
YEAR
1999
2000
DISTANCE
CUTTIME
520 ºC
730 ºC
1030 ºC
No cutting
F-test†
Estimate
Unit
SE
11***
1.48
1.58
kg
kg
0.027
0.027
8**
0.013
0.061
0.081
0.061
0
-0.11
kg/cm
0.0045
0.029
0.030
0.036
0.0088
3*
153***
NEIGHB
† * ** ***
, , - Significant at P<0.05, P<0.01 or P<0.001.
kg difference
compared to
No cutting
kg/NEIGHB
A linear model with varying distances to neighbour trees provided the best fit. All together
studies on inter- and intra-specific competition shows that competition between plants decreases
with increasing distance, i.e. the need for control is largest for the weed closest to the beet. This
conclusion extends the challenge to control weeds in the sugar beet row by cutting.
2.1
FRESHWEIGHT BEET (kg)
1.8
1.5
1.2
0.9
0
4
8
No 12
weed
DISTANCE (cm)
Figure 1. Mean beet fresh weight and standard deviation with weeds at 2, 4 or 8 cm distance or no
weeds in 1999 (solid) or 2000 (hollow/dotted). Each point is the mean values of
approximately 100 (1999) or 200 (2000) samples.
There was a significant effect of postponing the cutting of the weeds to mid June (Table 2). In
1999 the fresh weight of beets were largest when the weeds were cut during mid June. This effect
was not significant in 2000 (Fig. 2).
Farahbakhsh & Murphy (1986) made a glass house pot experiment to study competition
between sugar beet and the weed species Avena fatua L., Alopecurus myosuroides L. and Stellaria
media L. The different time of emergence of the species and plant density were important factors of
284
the severity of crop yield loss. There was no competition effect from the weeds on crop yield if the
weeds were removed just before the true six-leaf stage. Similar to those findings we found a
significant higher yield when the cutting of the weeds was postponed until mid June (approximately
2 months after emergence) (Figs. 2 and 3). Our results suggest that the optimal period of weed
cutting is a period between the final flush of weed emerge and the mutual overlapping of the leaves
and roots of the species. Mid June was also a period were the weed species were susceptible to
cutting. A higher weed level competition, e.g. higher weed density may change this conclusion.
FRESH WEIGHT BEET (kg)
2.00
1.75
1.50
1.25
1.00
200 No weed 400
600
800
1000
No
cut
1200
CUTTIME (ºC)
Figure 2. Mean beet fresh weight and standard deviation when weeds were cut at 520, 730 or 1030
ºC daily degree days, no cutting or no weeds as control in 1999 (solid) or 2000
(hollow/dotted). Each point is the mean values of approximately 80 (1999) or 160 (2000)
samples.
There were no significant interactions between date of cutting and the other factors i.e. sugar
beets did not gain from increasing the asymmetric competition between the species.
25
WEEDDW (g)
20
15
10
5
0
400
600
800
1000
No cut
1200
CUTTIME (ºC)
Figure 3. Mean weed biomass (WEEDDW) and standard deviation when weeds were cut at 520,
730 or 1030 ºC daily degree days or no cutting as control in 1999 (solid) or 2000
(hollow/dotted). Each point is the mean values of approximately 80 (1999) or 160 (2000)
samples.
285
The relation between harvested weed biomass (WEEDDW) and CUTTIME is shown in Fig. 3.
There was a significant decrease in weed biomass when postponing the cutting until mid June or
later both years. Hence, our results indicate that it is an advantage to postpone one weed control
cutting until mid June or later to reduce the weed biomass amount and to increase the beet yield.
The number of neighbours to the single beet had a significant reducing effect on the single beet
yield (Table 2) which could be described by a weighted regression line on the mean values of
approximately 0.33 kg per neighbour beet (NEIGHB) (Fig. 4). Beets compensate for the extra space
arisen by a missing neighbour by growing bigger itself. Previous research showed that one to four
missing beets in a row resulted in a yield decline comparable to only 0.22, 0.86, 1.08, or 1.78
normal beets (Lindhard & Jørgensen, 1928). Further, increasing space from 600 - 2600 cm2
increased a single beet size approximately linear from 0.4 to 1.5 kg whereas the total beet yield per
area was constant and approximately 6 ton per ha. A study of the role of numbers of neighbours on
individual plant growth rate has also been presented for P. rigida (Weiner, 1984). The result of the
study showed that the number of neighbours was a significant variable describing individual plant
growth rate, which supports our experimental results.
2.8
y = 2.82 - 0.33x
2
FRESHWEIGHT BEET (kg)
R = 0.93
2.1
1.4
0.7
Samples:
5
33 41
114
1
2
88
166
94
140
49
102
14
32
3
16
5
7
8
0.0
0
3
4
5
6
NEIGHBOURS (no)
Figure 4. Regression line (dotted) of the mean beet fresh weight as a function of neighbour number
weighted with number of samples (given) and the standard deviation for the means
(solid).
Precise detection of the position of the sugar beet or the position of weeds in the row is
necessary for efficient mechanical weed control in the row. A system combining geo-referenced
seeds of e.g. sugar beets with Real Time Kinematics - Global Positioning System and a sensor or
computer-vision for single plant detection could reconstruct the individual positions of a sugar beet
plant and make robotic steering of e.g. a flail disc or a laser realistic. Our results indicate that it is
important to remove the weeds closest to the beet and hence a mechanically robust and precise
system is needed.
286
References
FARAHBAKHSH A & MURPHY KJ (1986) Comparative studies of weed competition in sugar beet.
Aspects of Applied Biology 13, 11 – 16.
HEISEL T, SCHOU J, CHRISTENSEN S & ANDREASEN C (2001) Cutting weeds with a CO2 laser. Weed
Research 41, 19-30.
HENDERSON CR (1982) Analysis of Covariance in the Mixed Model: Higher-Level,
Nonhomogeneous, and Random Regression. Biometrics 38, 623-640.
JONES PA, & BLAIR AM (1996) Mechanical damage to kill weeds. In: Proceedings Second
International Weed Control Congress, Copenhagen, Denmark, 949-954.
LINDHARD E & JØRGENSEN M (1928) Om betydningen af spring i roemarkens plantebestand og om
udbyttets afhængighed af plantebestandens tæthed. Tidskrift for Planteavl 34, 565-595.
NAWROTH P & ESTLER M (1996) Mechanische Unkrautregulierung ohne Eingriff in das
Bodengefüge – Gerätetechnik, Prüfstandsversuche, Ergebnisse. Zeitschrift für
Pflanzenkrankheiten und Pflanzenschutz. Sonderheft XV 1996. 423–430.
PIKE DR, STOLLER EW & WAX LM (1990) Modelling soybean growth and canopy apportionment in
weed-soybean (Glycine max). Weed Science 38, 522-527.
SARPE N & TORGE C (1980) Der Einfluss einiger Unkrautgesellschaften mit dominanten Arten der
Gattungen Sinapis, Setaria, Erigeron, Amaranthus, Cirsium und convolvulus auf die
Wurzelproduktion der Zuckerrübe. Tagungsbericht der Landwirtschaftliche Wissenschaft,
DDR, Berlin, 182, 105-112.
WEINER J (1982) A neighbourhood model of annual plant interference. Ecology 63, 1237 – 1241.
WEINER J (1984) Neighbourhood interference amongst Pinus rigida individuals. Journal of Ecology
72, 183 – 195.
WEISBERG S (1985) Applied Linear Regression. Wiley series in probability and mathematical
statistics. John Wiley & Sons. New York. 324 pp.
287
Semi-automatic machine guidance system
J. Meyer
Technische Universität München
Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt
Department für Biogene Rohstoffe und Technologie der Landnutzung
Fachgebiet Technik im Gartenbau, Am Staudengarten 2
85354 Freising-Weihenstephan
Tel: +49 8161 713448, Fax: +49 8161 713895
Mail: Meyer@tec.agrar.tu-muenchen.de
Abstract
The development of automated machine guidance systems is a necessary prerequisite for an
increased use of physical methods for weed control. Because of very different crops (size and
morphology) in horticulture, remote sensors (e.g. infrared or ultrasonic sensors, vision systems)
should generally be preferred (HEMMING 2000). The occurrence of measurement mistakes, missing
plants in row, hazardous reflections and so on imposes the use of closed loop control systems,
which can compensate automatically these problems (MEYER, HARTMANN 1999). On the other hand
the human eye is a very powerful (rapid and precise) sensor which can easily overcome most
measurement problems. Therefore a guidance system was put together, which consists of a colour
video system on the weeder, a monitor for the tractor driver and an active (electrical) lateral
guidance system for the weeder. The tractor driver has to fulfil three tasks - steering the tractor and
monitoring and steering the weeder. In the experiments the guidance quality was monitored at
different driving velocities .
Introduction
The preciseness of guidance along a row of plants is directly influenced by the driving velocity and
the quality of the sensor and the mechanical steering system. For rear mounted machinery a second
worker normally is doing the steering which is cost intensive and to some extent limiting the
driving velocity as well. To solve these problems vision systems are being tested. But these are
unfortunately subjected to lots of measurement problems and are not working fast enough at bad
measurement conditions. As it can be expected, that the reliability of vision systems will improve
rapidly, in a first step a half automatic mechanical solution was carried out.
Material and Methods
The variation of the plant location along a plant row is depending on two factors:
x the variation between subsequent plants due to the planting or seeding process and
x the variation of the row itself, depending of the quality of the tractor or machine movement.
Whereas in the first case the variation normally should be overcome by a security distance between
e. g. weeder and crop row, in the second case the guidance system has to deal with the problem. To
demonstrate the situation and define the necessary movements, various measurements about the
variation of plant locations in a row have been carried out (HARTMANN 1999) with a geodimeter
measurement device (Figure 1). The absolute row position could be determined by measuring
distance from the measurement device and angle to a known subject, in this case a church tower
(Figure 1). The relative accuracy was determined by measuring the distance of the plant from a
defined center line.
288
plant row
Geodimeter 4000
Figure 1: Measurement of the absolute location of a plant row (Römer 2001)
As the main problem for the row guidance is the ad hoc variation, the driving/guidance experiments
were carried out with several defined “artificial” crop rows, one of which is shown in figure 2. The
artificial rows were defined in that way, that common problems like uneven rows, ad hoc jumps of
the seeder or inaccurate driving of the tractor were simulated.
Figure 2: Artificial crop row for testing purposes
289
Results
The investigations on a closed control loop automatic guidance system in a test frame (HARTMANN
1999) have clearly shown the necessity of disconnecting driving velocity and lateral machine
guidance as far as possible. Moreover the hydraulic systems of (especially old or lightweight)
tractors often are not suitable to guaranty an undisturbed direct control of the rear mounted
machinery. Because of that problems an electric motor has been chosen to carry out the lateral
movement of the guidance system.
The video-based lateral guidance system consists of three main parts:
x a colour video camera (dust and water protected) aiming at the plant row
x a colour video monitor in the view of the tractor driver (Figure 3)
x an electric linear motor on the weeder (Figure 4) being controlled by manual switches from the
tractor driver (Figure 3).
The tractor driver thus has three tasks
x Driving the tractor along the crop row (or in the furrow of the crop bed)
x watching the weeder on the video monitor
x steering the weeder along the crop row.
In the experiments the function of the electric lateral guidance system should be tested in respect of
the mechanical reliability, the necessary displacement width, the displacement speed and the
possible driving speed with the complete system (tractor, weeder and driver).
Figure 3: The video monitor and the switches in front of the tractor driver
290
Figure 4: The electric lateral guidance system
The variation of the plant positions in a crop row is depending directly of the planting or seeding
quality. As a matter of fact in principle this variation is so small, that in most cases a security
distance between the weeding tool (or any other tool) or the width of protecting tunnels is large
enough to avoid damage on the crop. In the case of seeded crops the minimal width could be around
6 cm, which is a well known practical value. Thus the ad hoc movement of the tractor and/or the
seeding or planting machinery is the main problem for the row accuracy (Figure 5).
Figure 5:
Relative Variation of the plant location of a planted or seeded crop
As a result of this, a maximum displacement of 15 cm of the electric system was chosen; that means
a displacement of 7,5 cm to both sides.
291
Every crop row was examined with 10 test drives, so that the increasing ability and experience of a
driver could be incorporated into the results. A typical result was, that up to a speed of 6 km/h it
was possible to drive and guide successfully the tractor and the weeder along a crop row.
Conclusions
In agriculture a general trend towards reduction of production costs is registered. One possibility is
to use improved lateral side guidance systems for agricultural machinery. The visual information
combined with the possibility to shift the agricultural machinery laterally from the tractor cab using
a control desk, provides an accurate adjustment following the plant rows. Thus a rear mounting is
possible, offering flexible handling and universal usability. The test results prove, that the lateral
guidance system allows a precise adjustment and a driving speed up to about 5-6 km/h which
corresponds with the average working speed for most weeders.
References
HARTMANN, P. 2000: Berührungslose Höhen- und Seitenführung von Traktoranbaugeräten in
Beetkulturen. Forschungsbericht Agrartechnik des Arbeitskreises Forschung und Lehre der
Max-Eyth-Gesellschaft Agrartechnik im VDI (VDI-MEG) 352. Dissertation, 175 p.
HEMMING, J. 2000: Computer vision for identifying weeds in crops, Gartenbautechnische
Informationen, Heft 50, Institut für Technik in Gartenbau und Landwirtschaft, Universität
Hannover.
MEYER, J. und HARTMANN, P. 1999: Automatische Führung von Hackgeräten, Landtechnik 3/99,
146-147.
RÖMER, H.-P. 2001: Einzelpflanzenorientierte Prozessführung im Freilandgemüsebau, Dissertation,
Freising-Weihenstephan, http://tumb1.biblio.tu-muenchen.de/publ/diss/ww/2001/roemer.html
292
Experimental assessment of the elements for the design of
a microwave prototype for weed control
C. De Zanche, F. Amistà, and S. Beria
Dept.Land and Agro-Forestry Systems, University of Padua,
Via Romea, 16 Agripolis, 35020 Legnaro, Padova
e-mail: federico.amista@unipd.it
Abstract
The study of the alternatives to the chemical weed control was oriented to verify the potential of the
electromagnetic waves, in particular microwave.
Several laboratory experiments, simulating the field conditions, was made in order to obtain enough
information useful to design a preliminary prototype to be verified in the next cycle of field tests.
The tests showed that the ground can absorb up to the 62% of the total amount of emitted energy,
thus indicating the necessity of a shield to increase the efficiency of the microwave generator.
However, considering the variability of the results, the experimentation showed that the microwave
irradiation can control the weed growth; in laboratory conditions an emission of 3 kJ, is required to
control 90% of the weed, but field simulation tests raise this threshold to 10 kJ.
293
Video assessment techniques to monitor physical weed management
N. M. Bromet and J.N.Tullberg
University of Queensland – Gatton
Queensland, Australia
Abstract
Current field techniques for weed monitoring using weed counts and ground cover generate
excessive data, and can often result in errors in multiple-plot experiments due to the excessive time
requirement of thorough assessment. This paper describes a video technique which allowed data
collection from multiple plots within a short timeframe. Initial trials demonstrated comparable
results to those from in-field observation and counting, and additional benefits including data on
weed size, cover and species identification.
Introduction
Weeds are a major pest in all cropping systems, reducing yields and product quality, and increasing
production costs. Soil degradation is often associated with mechanical weed control, and
environmental health concerns with herbicide control. In the national survey, financial returns of
winter cropping systems were reduced by a total of $1.2 billion in the 1998-99 season (Medd et al.,
2001).
Weed mapping on a field scale gives the ability to monitor the effectiveness of past or current weed
management and there is considerable interest in new, satellite-image technology to assist this
process. Current systems do not offer the spatial resolution and mission flexibility required for
practical weed patch identification and mapping on a field scale (Lamb and Brown, 2001), because
the best available images have a single-pixel resolution of only 1m2.
A system with higher resolution is needed for this task, and a simple hand-held video camera can
provide this, although spatial coverage is limited. Current developments in video and PC -- based
image processing technology allow the development of a high-accuracy system of crop/weed data
collection and analysis.
This paper describes a simple video-assisted monitoring system, and its testing in comparison to
direct observation and counting in a preliminary trial of methodology available to investigate high
precision guidance in physical weed control.
Methodology
The preliminary trial was established using 48 plots of 7m x 1.25m to provide 12 treatments with 4
replicates in a randomised complete block design. Treatments represented varying mechanical
management techniques, and guidance for this preliminary trial was achieved using a taught steel
cable between pairs of steel posts for physical guidance of planters and weed management
equipment. Black barley was sown at 150kg/ha in 25cm rows throughout this area.
294
Arrangement of the 12 treatments in four replicate blocks (A-D) is illustrated in (Fig.1).
Mechanical weed control treatments were applied at a speed of approximately 1 m s-1 and 2 cm
depth at 2-week intervals, except as indicated:
1.
2.
3.
4.
5.
6.
Weedy (no weed control)
Weed-free (hand weeded)
Sweep weeding treatment
Sweep at 4-week intervals
Rake weeding treatment
Rake at 4-week intervals
7. Sweep at 4 cm depth
8. Rake at 4 cm depth
9. Sweep at 2 m s-1
10. Rake at 2 m s-1
11. Sweep touching plants
12. Rake touching plants
A
N
12
2
9
11
4
10
B
5
6
3
7
1
8
1
9
2
4
8
6
C
10
5
12
11
3
7
8
2
12
5
9
11
D
4
6
10
7
3
1
6
12
8
1
7
2
3
9
11
10
4
3
Figure 1. Layout of trial plots (numbers indicate treatments, letters indicate blocks).
Weed assessments by direct observation and video methods were performed a few days after each
set of physical weed control treatments, and final weed and crop dry matter assessments taken at
crop maturity. The comparison reported here was made three weeks after planting, and four days
after the first set of weed control treatments were applied, using data from block A.
Direct observation and counting was performed in block A, within sections of one row width
(25cm) by 1m, and other manual techniques (line, quadrat and line/quadrat) used in other blocks.
Weed numbers from this field procedure were processed (using Microsoft® Excel®) and a surface
area graph constructed.
A hand-held digital video camera (Panasonic® DS88a) was used in the vertical plane at 2m
elevation to capture a 1m swath over all blocks. Movement of the camera was controlled using
inbuilt image stabilisation , and verbal messages used to identify treatments. Images from the video
camera were first transferred to the computer using Leadtek® Capview TV® and saved in mpeg
format. This video material was then scrolled through to provide screenshots at set intervals.
Images for one run were assembled using a ruler to ensure accurate scaling. These images were
imported into Ulead® Photoimpact® where filters were applied and counts performed, so the values
could be entered into Excel® and a corresponding surface area graph prepared.
Results
The digital video provided excellent image quality. Pixel resolution was high allowing easy
identification of small weeds and differentiation between weed seedlings when they would
otherwise appear as one weed or an indistinguishable mass.
295
The capacity for post-production image manipulation was extremely valuable. Images selected
from the video could be enhanced using filters to make identification easier as illustrated in Fig. 2.
An original image (left) can be compared with the image enhanced using a pink to yellow filter,
followed by a red to purple filter to provide a contrast in background, and a gold filter to enhance
weeds (right). This process avoided the danger of overlooking -- for instance – small, red-coloured
weed seedlings (yellow arrow) and smaller weeds.
The cut and paste function in the graphics program also allowed seedling images to be transferred to
a reference card, and aid species identification.
Figure 2. Comparison between the original (left) and digitally enhanced images (right).
Discussion
Results of using the two assessment systems are compared in Fig. 3, which illustrates the outcome
of direct observation and counting (left) and video assessment (right). The data demonstrates a
slight variation in weed counts in areas of high weed density, where weeds growing close to the
crop row were obscured from the camera by overhanging leaves. The overall pattern of weed
distribution using both techniques nevertheless appears to be very similar, particularly in respect of
major features such as weed free zones.
Where accuracy of weed counts close to and within the row is important, a perspex crop shield, or
even a simple deflector would allow the camera an unobstructed view of this area, in addition to the
interrow area.
This preliminary trial demonstrated the scope for multiple assessments over a very short timeframe,
which would eliminate errors of comparison due to time-lapse between direct visual observation of
treatments. In the absence of obstructions to the camera's view, the video system was a more
accurate method of recording weed numbers, and a very convenient method of recording weed size,
composition and physical damage to the crop.
296
Figure 3 Comparison of weed counts, in-field (left) and video technique (right).
The video procedure was estimated to have reduced the overall field and laboratory time required to
assess weed management treatments from approximately 4 h per block for visual field observation
and counting to 2.25 h per block. The less precise quadrat and line methods took longer than this. In
the high-intensity sunlight conditions of subtropical Queensland, this large reduction in field work
time with the video procedure was also appreciated by the operator.
This technique could equally well be applied by conventional photography and scanning, but the
digital video process was more convenient, and less costly.
The outcome of the preliminary trial confirmed that a simple video procedure for assessing weed
management treatments was substantially faster, and provided weed count data of equal or greater
accuracy than that achieved by visual observation and counting in the field. The video system also
yielded a richer data set, which included information on cover, species and crop damage, while
making the whole process more comfortable for the operator.
297
Acknowledgments
This work was supported by the Australian Centre for International Agricultural Research, under
Project 96/143 -- Sustainable Dryland Grain Production.
References
AUERNHAMMER H (2001). Precision Farming – The Environmental Challenge. Computers and
Electronics in Agriculture 30, 31-43.
LASS LW , CARSON HW AND CALLIHAN RH (1996). Detection of Yellow Starthistle
(Centaurea solstitialis) and Common St. Johnswort (Hypericum perforatum) with Multispectral
Digital Imagery. Weed Technology 10;3, 466-474.
LAMB DW AND BROWN RB (2001). Remote-Sensing and Mapping of Weeds in Crops. Journal
of Agricultural Engineering Research 78;2, 117-125.
MEDD R, REW L AND JONES R (2001). Cost of weeds in cropping systems. In: Proceedings
2001 Technology Developments in Weed Management, Dalby Agricultural College, 6-8.

EWRS Physical and Cultural Weed Control Working Group

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