Folie 1 - Bayerische Landesanstalt für Landwirtschaft

Irrigation experiments with hop
on sandy and loamy soils in the Hallertau
Tobias Graf1,3, Michael Beck2, Johann Portner1, Michael Mauermeier1, Daniel Ismann1, Margret Maier1,
Urs Schmidhalter3
1) Bayerische Landesanstalt für Landwirtschaft, Institut für Pflanzenbau und Pflanzenzüchtung, Wolnzach/Hüll, Germany
2) Hochschule Weihenstephan-Triesdorf, Freising, Germany
3) Technische Universität München, Chair of Plant Nutrition, Freising, Germany
Results and Discussion
Introduction
Predictions of climate change and drought spells, like in summer 2003, have raised
the question whether supplementary irrigation is needed in the hop growing regions
of Germany. Whereas for other hop growing regions such as the Yakima valley in the
US and Saaz in the Czech Republic, it is well established that irrigation stabilizes and
increases yield and quality of hop, such knowledge is scant in the hop growing regions
of Germany.
A three-years-irrigation experiment with different irrigation regimes was therefore
conducted on two sites with sandy and loamy soil and started in 2012 to investigate
whether:
Soil tension measurements
SWT measurements were mostly consistent but not well suited for irrigation scheduling
due to a less reliable prediction of the water demand. Since SWT measurements reflect
only a small rooting volume they are of limited usefulness to predict the plant´s water
demand, which was further corroborated by root excavations.
1) an objective irrigation management with soil water tension (SWT) or soil water
content based measurements is feasible,
2) irrigation increases the yield and alpha-acid content of hop and
3) Drippers should be installed aboveground or subsurface?
Materials and Methods
Two field trials with six different treatments were established in early 2012 in hop
fields with the variety Herkules. The experiments differed only in soil type.
Six different water regimes were compared:
Water output
SWTs at 150 – 600 hPa thresholds resulted in too small amounts of water given to the
plants. For the intensively irrigated treatment AG150 the water supply was therefore
increased in 2014.
Irrigation [mm] in
Pressure compensated irritec ©
multibar drip lines with a
distance of 50 cm and a water
output of 1.1 l/h were used.
-
Non-irrigated Control
low SWT (<150 hPa), aboveground AG150
medium SWT (<300 hPa), aboveground AG300
increased SWT (<600 hPa), aboveground AG600
medium SWT (<300 hPa), subsurface beside the row SSR300
medium SWT (<300 hPa), subsurface in the middle of rows SSM300
with six replicates each.
2012
2013
2014
Variety
Sandy soil
Loamy soil
Sandy soil
Loamy soil
Sandy soil
Loamy soil
AG 150
42.5
34.7
53.2
66.4
143.7
138.9
AG 300
28.5
45.1
36.6
59.4
16.9
35.4
AG 600
18.0
25.2
28.9
36.1
17.6
44.0
SSR 300
29.8
36.9
36.6
62.7
16.9
35.5
SSM 300
29.1
32.7
36.6
61.2
16.9
37.7
Precipitation [mm]
(May - Sept. 15)
433.2
487.1
507.4
419.8
429.4
351.0
Yield and Quality
Yield or alpha-acid contents of the irrigated treatments did not increase throughout the
three years compared to the non-irrigated treatment. Furthermore the evaluation in
2013, being temporarily a very dry year, was compromised by hail and only to a
limited degree assessable. In general, the years 2012-2014 reflected average
conditions in terms of rainfall and other meteorological conditions.
SWT was measured with Watermark (WM) sensors within the row, between the plants
and under a dripper at 30 cm and 60 cm soil depth.
The sensors installed in 30 cm soil depth were used for the irrigation decision. The
treatments with subsurface drip lines received irrigation comparably as the medium
irrigated treatment AG300. Irrigation started at the end of June or beginning of July
after plowing the plant rows. Each measuring was thrice replicated.
Conclusion
Irrigation was not required in the investigated sites in the Hallertau. With average and
uniform rainfall occurring during the growing season, additional water does not
increase yield and the alpha acid content.
It is expected that only in very dry years or on sites where soil compaction hinders a
widespread root development, irrigation may be required for enhancing plant growth.
Neither advantages nor disadvantages of aboveground or subsurface positioning of
drip lines were evident.
Drip irrigation may not be the optimal technique to withstand drought spells in the
Hallertau since root growth may be stimulated in shallow soil zones and rain might be
used less effective. Further research is required to substantiate this.
Acknowledgement
We want to thank the hop farmers Stefan Wöhrmann and Eduard Huber, for their support and providing us with the opportunity to investigate the influence of irrigation on their sites.
We also thank Sebastian Grünberger, Felix König, Florian Huber and Monika Pichlmeyer for their help during the irrigation experiment. Moreover we want to thank the both teams of the
Hop Research Center and Plant nutrition. This study was funded by the Deutsche Bundesstiftung Umwelt (DBU) Az.: 27866 and the Hopfenverwertungsgenossenschaft e.G. (HVG)
Bavarian State Research Center for Agriculture,
Institute for Crop Science and Plant Breeding
Kellerstraße 1, 85283 Wolnzach, www.LfL.bayern.de
Corresponding author:
tobias.graf@lfl.bayern.de or tobias.graf@tum.de