Water Extractable Trace Elements in Poultry Litters and

©2007 Poultry Science Association, Inc.
Water Extractable Trace Elements in Poultry
Litters and Granulated Products
G. S. Toor,*1 B. E. Haggard,† and A. M. Donoghue‡
*Soil and Water Science Department, Gulf Coast Research and Education Center,
Wimauma, FL 33598; †Biological and Agricultural Engineering,
University of Arkansas, Fayetteville 72701; and ‡USDA-ARS Poultry
Production and Product Safety Research Unit, Fayetteville, AR 72701
SUMMARY
Poultry litter contains many trace elements such as As, Cu, and Zn, and its land application
may lead to the accumulation of these elements in soils, especially near the soil surface. The
objectives of this study were to determine the total amount of trace elements and evaluate the
effect of litter granulation and various litter to water extraction ratios on water extractable trace
elements in 8 raw and granulated litter products. Granulated litters that contained urea,
dicyandiamide, or hydrolyzed feathermeal had significantly lower contents of total As, B, Cu, Mn,
and Zn than untreated litters because of the dilution of litters with additives. Trace element
concentrations (mg/L) in the water extracts of the various poultry litters generally decreased when
extraction ratios (litter to water) shifted from 1:10 to 1:250, or as the amount of poultry litter
decreased with a constant water volume (200 mL). But, the water extractable content of trace
metals (mg/kg) generally increased from an extraction ratio of 1:10 to 1:200, with values similar
at 1:200 and 1:250 extraction ratios. Based on our results, we suggest using a 1:200 extraction
ratio when evaluating water extractable As, Cu, and Zn in poultry litters. The estimated land
application rates of trace metals, when poultry litter is applied on the basis of total P content,
were considerably lower than the trace metal loadings allowable under the current environmental
regulations governing biosolids and other materials with measurable amounts of trace metals.
The laboratory water extractions of poultry litters and granulated products have increased our
understanding of the potential risks to water quality posed by the land application of poultry litter
and will contribute to the development of base knowledge needed to define land application practices
that are protective of soil and water quality.
Key words: poultry litter, granulation, water extractable trace element, litter water extraction,
arsenic, copper, zinc
2007 J. Appl. Poult. Res. 16:351–360
DESCRIPTION OF PROBLEM
United States Environmental Protection
Agency Part 503 rule [1] regulates the application
of biosolids based on the total contents of As,
Cd, Cu, Hg, Mo, Ni, Pb, Se, and Zn. For instance,
1
Corresponding author: gstoor@ufl.edu
the application of biosolids to soil should not add
greater than 2, 75, and 140 kg/ha per yr of As,
Cu, and Zn, respectively. Recently, litigation in
Arkansas and Oklahoma has targeted the land
application of poultry litters and specifically identified several trace elements in poultry litter, (i.e.,
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Primary Audience: Environmental Managers, Nutritionists, Poultry Producers, Researchers
352
might be used. Therefore, our objectives in this
study were (i) to determine the total amount of
trace elements in raw/ground poultry litters and
granulated poultry litter products, (ii) to evaluate
the influence of poultry litter to water extraction
ratios on the measure of soluble trace elements
in the poultry litters and granulated products, and
(iii) to estimate the loading rate of trace elements
to soil when these litters and granulated products
are land applied on the basis of their total P
contents.
MATERIALS AND METHODS
Poultry Litter Collection
Poultry litters (mixture of feces and bedding
material) were collected from 2 poultry farms in
Northwest Arkansas and granulated at facilities
located in Pennsylvania and Arkansas. Poultry
litter from 1 farm near Decatur, AR, was ground
to pass through a 5.8-mm mesh screen and thoroughly mixed using a New Holland 352 feed mill
mixer [14]. The ground and mixed poultry litter
was delivered to Mars Mineral Inc. (Mars, PA)
and was placed in a holding bin. Feed grade urea
[15] and dicyandiamide (DCD) [16] were placed
in an adjacent bin and used during the process
to produce some of the granulated products. The
poultry litter (and additives) were fed into a bench
scale granulator [17] with vibrating screw feeders
[18]; water was used as the binding agent in the
granulation process. After granulation, granulates
were moved to a vibrating fluid bed dryer at
232°C and dried to 121°C. Dried granulates were
screened to pass through a 4.75-mm mesh screen,
but not a 0.85-mm mesh screen.
Five treatments resulted from this litter
source: 1) raw poultry litter (raw litter no. 1);
2) ground poultry litter (ground litter no. 1); 3)
granulated poultry litter (granulated litter no. 1);
4) granulated mixture of poultry litter plus urea
(granulated litter no. 1 with urea); and 5) granulated mixture of poultry litter plus urea and DCD
(granulated litter no. 1 with urea and DCD). For
100 kg of granulated product, the amount of urea
added was 25 kg (25%) for the granulated litter
no. 1 with urea, whereas the granulated litter no.
1 with urea and DCD contained 22 kg of urea
(22%) and 2.3 kg of DCD (2.3%). Dicyandiamide
is a nitrification inhibitor, often used in agricultural practices to reduce nitrate losses [19]. The
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As, Cu, and Zn) where there are no current regulations on the maximum amount that can be applied
to soil. In the United States, animal manures are
typically land applied based on P management
practices, resulting in the application of measurable amounts of trace elements to soils. For example, Nicholson et al. [2] estimated that animal
manure contributes 25 to 40% of the total annual
Cu and Zn inputs to soils in the England and
Wales. The excessive land application of poultry
litter can result in build up of trace elements near
the soil surface [3, 4, 5] and can lead to the loss
of trace elements to waters through leaching [6,
7] and surface runoff [8]. Van der Watt et al. [9]
reported build-up of phytotoxic levels of Cu, Mn,
and Zn in soil that received 6 mg/ha per yr of
poultry litter for 16 yr.
Elevated levels of trace elements are excreted
in the manures as the animal diets usually contain
trace elements greater than the animal requirements due to the safety margins. The recommended amounts of Cu and Zn in poultry diets
are 4 and 50 mg/kg, respectively, whereas Cu
and Zn content in poultry diets have been reported
to exceed 30 and 100 to 150 mg/kg, respectively
[2, 10]. Trace elements are needed to carry out
important enzymatic and nonenzymatic functions
in the poultry [11, 12]. For example, As has been
used in the poultry diets as 3-nitro-4-hydroxyphenylarsonic acid (Roxarsane) or 4-aminophenylarsonic acid (p-ASA) to prevent coccidiosis, increase weight gain, and improve feed efficiency
[13]. Similarly, Cu and Zn have been used as
growth promoters or biocides in the poultry feed
[12, 13].
To manage potential long-term impacts of
trace elements in soils, it is important to first
quantify total and soluble trace elements in animal manures and then identify soils that are most
vulnerable to trace elements loss via surface runoff and leaching. Little information is available
on the trace element inputs to soils from today’s
animal manures, whose chemical composition
may be different from the past manures because
animal diets are often changing, driven by animal
genetics and variable costs of diet ingredients. At
the same time, efforts are underway to balance
nutrient (particularly P) inputs and outputs in intensive animal production regions by developing
off-farm uses of manures such as in turf, lawn,
and gardens where granulated poultry litters
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18.3 ± 0.4a
15.5 ± 0.5b
44.9b
60.6a
1
1 with urea
1 with urea and DCD
2 with feathermeal
0.9ab
1.2a
0.9ab
0.4b
1.0c
0.4c
22.7
23.6
22.7
21.9
17.7
16.8
±
±
±
±
±
±
g/kg of DM
P
30.6c
31.1c
30.6c
41.5b
141.3a
142.9a
N
±
±
±
±
±
±
2a
1a
2a
1a
2b
2b
24 ± 1a
20 ± 1b
43
44
43
41
33
32
As
±
±
±
±
±
±
2a
2a
2a
2a
3b
1b
122 ± 4a
101 ± 2b
69
68
69
66
55
54
B
±
±
±
±
±
±
25b
24a
25b
16b
21c
20c
339 ± 10a
292 ± 6b
599
647
599
591
460
453
Cu
±
±
±
±
±
±
131ab
69ab
131ab
119a
54ab
10b
544 ± 22b
697 ± 23a
561
561
561
636
475
419
mg/kg of DM
Fe
±
±
±
±
±
±
3a
20a
3a
7b
19c
22d
453 ± 10a
381 ± 10b
678
688
678
651
575
537
Mn
±
±
±
±
±
±
4b
9a
4b
1b
17c
20.5d
417 ± 14a
364 ± 6b
615
642
615
620
517
490
Zn
Source no. 1
Raw litter no. 1
Ground litter no. 1
Heated litter no. 1
Granulated litter no.
Granulated litter no.
Granulated litter no.
LSD (0.05)
Source no. 2
Ground litter no. 2
Granulated litter no.
LSD (0.05)
2 with feathermeal
1
1 with urea
1 with urea and DCD
870
163
169
106
46
90
5,291 ± 85
4,542 ± 111
224
6,429 ±
7,043 ±
8,029 ±
7,432 ±
4,934 ±
4,839 ±
663
P
±
±
±
±
±
±
6
4.5
2.8
5.0
1.5
3.3
1.6
13 ± 5.8
10 ± 5.6
12
30
28
24
25
20
20
As
±
±
±
±
±
±
9
4.7
4.7
6.6
7.0
3.2
4.1
100 ± 1.9
90 ± 2.8
6
50
53
58
52
45
44
B
± 14.6
± 1.4
± 7.5
± 8.2
± 3.4
± 2.7
14
127 ± 1.5
95 ± 1.9
4
244
263
87
243
135
149
mg/kg of DM
Cu
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Poultry litter treatment
4.5
2.3
1.0
3.5
0.3
0.6
13.0 ± 0.3
13.1 ± 0.1
0.1
35
43
54
60
20
18
±
±
±
±
±
±
5
14
3.7
3.5
3.9
0.8
1.2
±
±
±
±
±
±
11
54 ± 0.9
42 ± 1.0
2
104
123
52
117
65
68
Mn
Fe
± 10.3
± 3.8
± 5.1
± 1.6
± 1.0
± 1.5
9
23 ± 1.5
17 ± 0.6
3
54
65
30
76
23
23
Zn
Table 2. Contents of water extractable elements at 1:200 litter to water extraction ratio in raw, ground, and granulated poultry litters where several granulated poultry litters
had urea, urea and dicyandiamide (DCD), or hydrolyzed feathermeal added as an additional N source
1
a–d
Values followed by different letters in the same column are significantly different at P < 0.05.
Total N and P data from Toor et al. [24].
2
Note: Raw litter no. 1 was heated to produce heated litter no. 1.
Source no. 1
Raw litter no. 1
Ground litter no. 1
Heated litter no. 12
Granulated litter no.
Granulated litter no.
Granulated litter no.
Source no. 2
Ground litter no. 2
Granulated litter no.
Poultry litter treatment
Table 1. Total contents of N, P, and trace elements in raw, ground, and granulated poultry litters where several granulated poultry litters had urea, urea and dicyandiamide
(DCD), or hydrolyzed feathermeal added as an additional N source1
TOOR ET AL.: WATER EXTRACTABLE TRACE ELEMENTS
353
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5.5 ± 0.3
4.6 ± 0.2
0.6
2.9 ± 0.1
3.4 ± 0.1
0.3
10.0 ± 0.2
6.4 ± 1.7
2.8
37.6 ± 0.9
32.6 ± 1.3
2.5
5.2
6.3
7.9
9.2
3.4
3.4
4.4
3.5
1.7
2.6
1.4
0.2
19.0 ±
22.2 ±
9.6 ±
18.8 ±
13.7 ±
16.1 ±
4.8
3.1
1.3
1.1
0.5
0.7
2.1
54.8 ± 24.8
51.1 ± 25.7
7.3
29.0 ± 0.9
29.3 ± 0.9
2.1
2 with feathermeal
1
1 with urea
1 with urea and DCD
Source no. 1
Raw litter no. 1
Ground litter no. 1
Heated litter no. 1
Granulated litter no.
Granulated litter no.
Granulated litter no.
LSD (0.05)
Source no. 2
Ground litter no. 2
Granulated litter no.
LSD (0.05)
% of total
40.8 ±
40.7 ±
14.5 ±
41.1 ±
29.4 ±
32.9 ±
3.0
72.1 ± 9.0
77.3 ± 5.7
83.7 ± 6.6
78.3 ± 10.7
82.1 ± 6.0
82.0 ± 5.8
13.5
69.9 ± 13.5
63.5 ± 5.8
54.9 ± 10.8
60.3 ± 3.1
61.2 ± 15.0
62.7 ± 1.6
17.3
28.5 ±
29.9 ±
35.5 ±
33.9 ±
27.9 ±
28.7 ±
4.3
4.8
2.0
2.1
0.7
1.4
1.0
82.0 ± 1.2
89.1 ± 2.2
4.0
1.7
0.7
0.9
0.3
0.1
0.5
8.8 ±
10.2 ±
4.9 ±
12.2 ±
4.4 ±
4.7 ±
1.5
± 0.7
± 0.5
± 0.1
± 0.4
± 0.1
± 0.1
0.7
Zn
Mn
Fe
Cu
B
As
P
Poultry litter treatment
raw poultry litter was heated at 180°C for 2 h
(heated litter no. 1) at our laboratory.
A second poultry litter source was obtained
from Organic-Gro Inc. [20]. At this facility,
ground poultry litter was passed through a 2.5mm vibrating screen and then mixed with hydrolyzed feathermeal before granulation. Two
treatments resulted from this litter source: 1)
ground poultry litter (ground litter no. 2); and 2)
granulated mixture of poultry litter and hydrolyzed feathermeal (granulated litter no. 2 with
feathermeal). This facility dried granulates to less
than 8% moisture to avoid composting during
storage and produces a commercially available
product (see http://www.organic-gro.com/40824.shtml).
Poultry Litter Extraction and Analyses
Total As, B, Cu, Fe, Mn, P, and Zn in the raw
and granulated poultry litters were determined, in
triplicate, using concentrated HNO3 and H2O2
digestion followed by inductively coupled
plasma-optical emission spectroscopy (ICPOES) analysis [21]. Water extractable (WE) As,
B, Cu, Fe, Mn, P, and Zn were measured by
extracting poultry litters, in triplicate, at poultry
litter (dry weight equivalent) to deionized water
ratios of 1:10, 1:50, 1:100, 1:200, and 1:250. For
example, the 1:10 ratio had 20 g of dry weight
equivalent of poultry litter mixed with 200 mL of
water (including ambient moisture in the poultry
litter), and this volume of water (200 mL) was
used in all extracts. The mixture was shaken for
2 h in a reciprocating shaker followed by centrifugation at 2,900 rpm for 20 min before filtration
through a 0.45-␮m nylon membrane. The filtered
aliquot from the various ratios was analyzed for
WE As, B, Cu, Fe, Mn, P, and Zn by ICP-OES.
Statistical Analyses
Descriptive statistics and 1-way ANOVA
with means separation using the LSD were performed by Genstat 4.2, 5th edition [22] to calculate means, SD, and to test for significant effects
of litter sources and extraction ratios on the trace
elements. Statistical comparisons were determined at P < 0.05.
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Table 3. Percentage of water extractable elements at 1:200 litter to water extraction ratio in raw, ground, and granulated poultry litters where several granulated poultry
litters had urea, urea and dicyandiamide (DCD), or hydrolyzed feathermeal added as an additional N source
354
TOOR ET AL.: WATER EXTRACTABLE TRACE ELEMENTS
355
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Figure 1. Concentrations of trace elements in aliquots from the water extractions at the various poultry litter to
water extraction ratios. The regression line represents the overall trend for all litters. DCD = dicyandiamide.
RESULTS AND DISCUSSION
Total Trace Element Contents
in Poultry Litters
Total contents of all trace elements were generally lower in the granulated products than
ground litter (Table 1), where granulation of poultry litter and addition of additives (i.e., urea, DCD
or hydrolyzed feathermeal) significantly reduced
contents of As, B, Cu, Mn, and Zn compared
with raw or ground litter with in each poultry
litter source (i.e., litter no. 1 or 2). This decrease
in trace elements content is attributed to the dilution of litter with additives in the granulated products, not because of the granulation process. As
a comparison, total P contents were also significantly lower in the granulated products, whereas
total N was significantly increased in the granulated products compared with ground litter because of the presence of N in the urea and hydrolyzed feathermeal. Trace element contents differed in poultry litters obtained from 2 sources,
likely from differences in poultry diets. For example, poultry litter no. 1 had greater contents of
356
Effect of Extraction Ratios
on Water Extractable Trace Element
Concentrations and Contents
in Poultry Litters
Concentrations of soluble As, B, Cu, Fe, Mn,
and Zn in the water extracts decreased with an
increase in extraction ratio from 1:10 to 1:250
(Figure 1). The concentration of As in the water
extracts from the various poultry litters was 1.05
to 2.35 mg/L at 1:10, which decreased to 0.05 to
0.12 mg/L at 1:250 extraction ratio. Moore et al.
[8] reported initial soluble As concentrations of
>0.2 mg/L in runoff from a soil amended with
poultry litter at 9 mg/ha, and it appears that concentrations of As in runoff waters from Moore
et al. [8] were in the range we observed at the
1:100 extraction ratio (0.13 to 0.29 mg/L). Moore
et al. [8] also reported soluble Cu levels in runoff
waters up to 1 mg/L, which is approaching the
US EPA drinking water maximum contaminant
level of 1.3 mg/L. In our litters, we observed
concentrations of Cu from 0.92 to 2.35 mg/L in
the water extract at the 1:100 extraction ratio
(Figure 1). The similarity of these soluble As and
Cu concentrations in our water extracts to runoff
concentrations of Moore et al. [8] indicates that
a quick water extraction of poultry litter in the
laboratory may help to assess the solubility and
runoff potential of trace elements from land applied poultry litter. This also supports our previous observation [24] that litter to water extraction
ratio from 1:100 to 1:200 may be the best indicator to assess the potential release of P and could
also be used for risk assessment of trace element
loss to water.
Although trace element concentrations (mg/
L) in the water extracts decreased with an increase
in extraction ratios from 1:10 to 1:250, the contents (mg/kg) of WE As, B, Cu, Fe, Mn, and Zn
increased with an increase in extraction ratio from
1:10 to 1:200 (Figure 2). Contents of WE As and
Cu were not significantly different between 1:100
and 1:200 extraction ratios, whereas WE B, Fe,
Mn, and Zn were significantly higher at 1:200 (5
to 13%) than 1:100 extraction ratio. Based on
these limited observations, we suggest using
1:200 extraction ratio to extract most of the WE
trace elements in poultry litters. It is important
to note, however, that concentrations of all trace
elements were lower at the 1:200 extraction ratio
than 1:100, and the concentrations of several trace
elements (e.g., Cd, Cr, and Mo) were below the
detection limits of ICP-OES beyond the 1:10 extraction ratio (data not shown). For example, at
the 1:10 extraction ratio, the concentrations of
Cd, Cr, and Mo were <0.10, <0.19, and <0.15
mg/L, respectively, for all litters. Therefore, if
the objective of the study is to determine the
concentrations of Cd, Cr, and Mo in litters, researchers should use lower extraction ratio (preferable 1:10) to obtain measurable amounts. The
following section focuses on the contents of WE
As, B, Cu, Fe, Mn, and Zn at the 1:200 extraction
ratio because this extraction ratio extracted most
of the soluble forms of these trace elements.
Water Extractable Trace Elements Contents
in Poultry Litters at 1:200 Extraction Ratio
Contents of WE As in litters and granulated
products ranged from 10 to 30 mg/kg (Table 2).
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As, Cu, Mn, and Zn than poultry litter no. 2 (Table
1). Among these 6 trace elements discussed, As
contents were least (20 to 44 mg/kg) followed
by B (54 to 122 mg/kg) then Cu, Fe, Mn, and
Zn, which were generally similar in magnitude.
However, the contents of Co (<0.6 mg/kg), Cr
(0.5 to 2.2 mg/kg), and Mo (0.7 to 1.5 mg/kg)
were least among all trace elements determined
via ICP-OES (data not reported).
The maximum allowed limits of As for land
application in biosolids is 41 mg/kg [1]; therefore,
raw or ground poultry litter no. 1 had As contents
(41 to 44 mg/kg) at or slightly more than the
biosolids limits. However, the granulated products from poultry litter no. 1 that included additives (i.e., urea and urea plus DCD) had As contents that were less (32 to 33 mg/kg) than the
biosolids limits for As content (Table 1). Similarly, the poultry litters from the other source (no.
2) had As contents approximately half of the
biosolids limits. The contents of Cu and Zn in
litters and granulated products (<647 mg/kg)
were well below the threshold limits for land
application of biosolids (1,500 and 2,800 mg/kg,
respectively) [1]; therefore in the short-term, litter
application may not affect the soil trace element
contents to a great extent. However, several previous studies have shown that long-term application
of poultry litters to soil can elevate trace element
contents above soils that do not receive manure
applications [5, 23].
JAPR: Research Report
TOOR ET AL.: WATER EXTRACTABLE TRACE ELEMENTS
Contents of WE B, Fe, Mn, and Zn were less
than 123 mg/kg for all poultry litters, whereas
WE Cu ranged from 263 mg/kg in the ground
litter no. 1 to 135 to 243 mg/kg in the granulated
litters (no. 1). In contrast, the contents of water
extractable P were significantly greater in the
heated litter (8,029 mg/kg) than other litters
whether granulated or not and significantly lower
in the granulated products that contained urea,
urea plus DCD, or hydrolyzed feathermeal (4,542
to 4,934 mg/kg) than raw and ground litters
(5,291 to 7,043 mg/kg).
Among trace elements, As, B, and Cu exhibited greater water solubility (15 to 89%), whereas
Mn and Zn were less water soluble (3 to 12%)
in litters (Table 3). In comparison, water extractability of P ranged from 28 to 36% at 1:200 for
all litters, with nonsignificant differences between
granulated litters that had urea, urea plus DCD,
or hydrolyzed feathermeal and ground litters with
in each litter source (no. 1 or 2). Likewise, the
percentages of WE As were not significantly different for the ground and granulated litters from
both sources, whereas WE Cu and Zn were significantly lower in the granulated products with
urea, urea plus DCD, or hydrolyzed feathermeal
compared with ground litter in each source. At
the 1:200 extraction ratio, 51 to 70% of As was
WE, which indicates that this element will be
readily soluble when poultry litter is land applied.
Organo-arsenic compounds such as roxarsane or
p-arsanilic acid, when added to feed, are apparently excreted by birds in relatively unchanged
chemical forms. Jackson et al. [10] fractionated
WE As in poultry litters and observed roxarsane
and p-arsanilic acid as major As contributors,
along with their metabolites (arsenite, arsenate,
mono- and di-methyl arsinate, and unknowns).
However, once organo–arsenic compounds present in poultry litter are applied to soil, the organic
forms break down into metabolites that vary in
mobility and toxicity [25, 26]. For example, the
soluble inorganic arsenicals are known to be more
toxic than the organic forms to the animal health
and the arsenites (AsIII) are more soluble, mobile,
and toxic than arsenates (AsV), which are
strongly adsorbed by soil constituents [27].
Contents and percentages of WE Cu were
greater than WE Zn for all litters (Tables 2 and
3). Copper and Zn are added to animal feeds as
a sulfate salt or oxide and presumably occur in
the litter in ionic form. However, both these elements can form stable complexes with the organic
matrix of litters; as a result, their mobility can
be affected when land applied [11, 28]. The percentages of WE Cu and Zn were significantly
reduced by 1 to 6% (Zn) and 5 to 8% (Cu) in
the granulated litters that had urea, urea plus
DCD, and hydrolyzed feathermeal when compared with ground litter for each source. This
may be due to the transformation of Cu and Zn
to less soluble forms during litter granulation that
involved heating and drying at higher temperatures. The observation that the heated litter no. 1
had significantly reduced WE Cu and Zn contents
also supports the transformation from soluble to
less soluble forms during drying at higher temperatures.
Among polyvalent cations, water solubility
was relatively low for Fe (6 to 22%), Mn (3 to
9%), and Zn (4 to 12%), indicating that these
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Figure 2. Water extractable elements expressed as
percent of water extractable (WE) elements at 1:250
extraction ratio for poultry litters. Values are means for
8 poultry litters for each element at each extraction
ratio. Standard deviation is shown by vertical lines.
a–d
Letters followed by the different letters for each
element are significantly different at P < 0.05.
357
358
JAPR: Research Report
elements are present in adsorbed forms and are
not easily released by water extraction (Table 3).
Also, the lower water extractability of Fe, Mn,
and Zn compared with other elements suggest
that these may be major cations responsible for
adsorbing anions such as As and P, which are
more soluble in the water extracts.
Implications of Trace Element Loading
in Intensive Poultry Production Regions
Figure 3. Estimated total and water extractable trace
elements loading from poultry litter application at the
100 kg of total P/ha. Standard deviation is shown by
vertical lines. a–cColumns within each element having
different letters are significantly different at P < 0.05.
NS = nonsignificant within each litter source (i.e., no.
1 or 2). DCD = dicyandiamide.
1.2 and 3.1 kg/ha, respectively, which is approximately 2-fold lower for Cu and similar for Zn
than our poultry litters. Nicholson et al. [2] calculated that at an application level supplying 250
kg of N/ha, poultry manures would add 1.1 and
0.5 kg/ha of Cu and Zn, respectively. It is important to be aware that trace element additions
to soils may vary from our calculated values and
among different studies because of the variability
of these elements in poultry litters or other manure types and due to the different land application practices, such as total N or P based, used on
the farms or regions. Importantly, the commercial
nutritionists need to be educated about the risks
to soil and water quality so that they can safely
modify nutrient margins not only for environmental purposes but also for sustaining commercial
operations.
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Poultry litter is a valuable source of organic
matter, major plant nutrients, and some trace elements; however, excessive addition of these elements in poultry diets results in greater amount
in litters and raises concerns about excessive element loading to soils. For example, Nicholson et
al. [2] reported that each year animal manure
applications contribute 1,821 mg of Cu and 5,247
mg of Zn to the England and Wales soils, which
corresponds to 25 to 40% of the total annual
inputs of these elements to soils. We calculated
the typical amounts of trace elements added to
soil if raw and granulated poultry litter products
are applied at rates supplying 100 kg total P/ha
per yr (∼90 lb of P/ac), in accordance with the
maximum allowable P inputs under P-based management practices in the Eucha-Spavinaw Basin
in Northwest Arkansas [29]. Although a greater
mass of granulated products that contained urea
(5,650 kg/ha), urea plus DCD (5,952 kg/ha), or
hydrolyzed feathermeal (6,452 kg/ha) would be
land applied than ground litter no. 1 (4,237 kg/
ha) or ground litter no. 2 (5,464 kg/ha) due to
the lower total P content of granulated products,
generally the total addition of As, Cu, and Zn to
soil would be similar from ground and granulated
litters (Figure 3). For example, raw or ground
litters and granulated products would add 0.13
to 0.19 kg of total As/ha, 1.9 to 2.7 kg of total
Cu/ha, and 2.3 to 2.9 kg total Zn/ha to soil, if
litter is applied at 100 kg of total P/ha. The total
addition of As from our litters with a 1-time
application is below the US EPA annual application limit of 2 kg/ha [1]; however, the greater
solubility of As in litters (WE-As: 0.07 to 0.13
kg/ha; 51 to 70% of total) may result in greater
addition of WE As to soils, as has been also
reported by Christen [30].
McBride and Spiers [31] calculated that if
dairy manures are applied at 150 kg P/ha, the
annual loadings of Cu and Zn would be about
TOOR ET AL.: WATER EXTRACTABLE TRACE ELEMENTS
to soil, dairy manure application would add 70fold greater Zn and 2,000-fold greater Cu than
from commercial fertilizers.
Clearly, to reduce the concerns of trace elements accumulations in soils, the best management practices should aim to decrease the output
of trace elements in animal manures. This may
involve dietary modifications to match trace element contents in feeds with animal requirements.
Research is evidently needed to better understand
utilization of trace elements by animals so that
the excessive addition of trace elements in diets
could be reduced. For example, Mohanna and
Nys [32] reported that reduction in dietary Zn
contents in poultry diets from 190 to 60 mg/kg
decreased Zn excretion in poultry litters by 75%,
and this reduction did not adversely affect enzyme activity or immune response of the chicks.
The knowledge gained by the research on the
trace element utilization by animals would help
to optimally balance rations so that the amounts of
trace elements in diets does not result in excessive
levels in manures, which would reduce the future
build-up of trace elements in soils when manures
are land applied.
CONCLUSIONS AND APPLICATIONS
1. Addition of urea, urea plus DCD, and hydrolyzed feathermeal to poultry litter during litter
granulation diluted total contents of As, Cu, and Zn by 10 to 25% compared with raw and ground
litters, without affecting water extractable contents.
2. An increase in litter to water extraction ratio increased water extractable contents of all trace
elements. It appears that 1:200 extraction ratio offers the best option to extract most of the water
extractable trace elements in poultry litters. However, at the 1:200 extraction ratio, several trace
elements concentrations were below the detection limits of ICP-OES, for which a lower extraction
ratio (1:10) needs to be used.
3. Addition of As, Cu, and Zn to soils with a 1-time application of poultry litter, whether granulated
or not, would be much lower than the US EPA annual application limits of trace elements for
biosolids; however, repeated application of litter will likely result in soil loading of trace elements
above environmental thresholds.
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In areas where animal manures have been
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Acknowledgments
This project was made possible by Organic-Gro Inc. and Mars
Mineral Inc.; without the cooperation of these companies, the granulated products would not have been evaluated in this study. Funding
for this project was provided by the US Poultry and Egg Association
Research Support Program, the US Department of Agriculture – Agricultural Research Service, and the University of Arkansas—Division
of Agriculture. We would like to thank Stephanie Williamson for her
dedicated work on this project during poultry litter extractions and
laboratory analyses. This project benefited from valuable consultation
with Daniel Pote and Tommy Daniel, and this manuscript benefited
from reviews by several anonymous technical reviewers.
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