3
COMPOSTING FOR INCREASING THE FERTILIZER VALUE
OF CHICKEN MANURE: EFFECTS OF FEEDSTOCK ON P
AVAILABILITY
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B. Vandecasteele1, B. Reubens1, K. Willekens1, S. De Neve2
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Environment, Burg. van Gansberghelaan 109, B-9820 Merelbeke, Belgium
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CONTACT: bart.vandecasteele@ilvo.vlaanderen.be, ILVO, Van Gansberghelaan 109, B-9820 Merelbeke
Institute for Agricultural and Fisheries Research (ILVO), Plant Sciences Unit, Crop Husbandry and
Ghent University, Dept. Soil Management, Coupure 653, B-9000 Ghent, Belgium
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ABSTRACT
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The application rate of poultry manure as organic fertilizer is restricted due to its low C/P and N/P ratio. This
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research was set up to find out optimal feedstock composition for composting chicken manure in order to
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create a soil improver with a higher value as organic fertilizer, and to assess the effects of this process on P
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availability in the end products. The research is based on two compost experiments with three treatments
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each, and the chicken manure composts were compared with the end products of green waste compost used
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as bedding material in chicken houses, centrally processed chicken manure and a stockpiled mixture of green
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waste compost and chicken manure. In the first compost trial, feedstock materials were compared for
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composting with fresh chicken manure. The chicken manure compost with 42.5 vol% bark in the feedstock
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had the highest quality as soil improver in terms of organic matter content, C/P ratio, C/N ratio and stability.
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Results of the second compost trial indicate that 10 vol% of fresh chicken manure is the upper limit in small-
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scale on-farm windrow composting above which nutrient losses become too high and the N/P ratio of the
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obtained fertilizer becomes too low. Stability of the product (expressed as oxygen uptake rate) had a major
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effect on P availability in the compost. Blending the chicken manure compost with biochar based on holm
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oak resulted in a more than proportional decrease in easily available P in the biochar-blended compost. P in
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poultry manure can be recycled through composting and be applied as an organic fertilizer with optimal
27
nutrient ratio and organic matter content when appropriate feedstock materials are selected and the amount of
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fresh manure in the feedstock mixture is restricted.
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Keywords: organic fertilizer, value-added soil improver, P recycling, wood chips, bedding material, biochar-
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blended compost, poultry litter
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1
INTRODUCTION
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For proper application as organic fertilizer it may be necessary to treat raw chicken manure: due to its
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variable composition, raw chicken manure is difficult to spread in a homogenous way. Storage over a longer
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period may be necessary as it is not always available at proper time of application in the field. Besides these
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bottlenecks the application rate of raw poultry manure as organic fertilizer is restricted due to its low C/P and
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N/P ratio and the risk of N and P losses [1]. To meet fertilization standards for reducing nutrient leaching, the
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total P and N content of poultry manure limits the application rate [1-3]. Long-term poultry litter application
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in pasture soil affected the P distribution in soil aggregate size fractions and may lead to P losses [4]. Several
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options for processing manure were tested previously, e.g. poultry litter granulation [2], composting of
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manure [1, 3,5-7] or biochar production with chicken manure as feedstock [8]. The process circumstances of
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biochar production affected the liming effect and nutrient release of different types of biochar based on
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chicken manure [8]. Application of additives is another option to change the properties of chicken manure:
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several additives can be supplied to slurries and manures to reduce P availability and leaching [9-10].
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Composting of manure [1, 3,5-7] or the solid fraction of the digestate remaining after the anaerobic digestion
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of cattle slurry constitutes a feasible treatment for reducing the volume for haulage and for the production of
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composts with an adequate degree of stability and maturity and the presence of value-added properties, such
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as suitable physical properties [11]. Composting of chicken manure mixed with other feedstock materials
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may result in a stable product rich in nutrients and organic matter, with a lower risk for P leaching [12] and
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higher C/P ratio. Compost can be stored for a longer period and is easier to apply in the field than raw
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chicken manure. Composting of poultry manure might have additional benefits, e.g. further decomposition of
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veterinary drugs, as recently the uptake of veterinary medicines by plants has been demonstrated for several
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compounds and plant species when chicken manure was used as fertilizer [13-16]. Composting of manure
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resulted in faster or stronger degradation of these compounds [17-18]. Increasing the quality and added-value
56
of compost is related to feedstock selection [19] and pre- and post-treatment of the compost, e.g. by
2
57
screening [20] or shredding [21]. Tognetti et al. [21] reported strategies to improve the OM (organic matter)
58
content of composts, but sometimes these strategies also resulted in a decrease in nutrient availability. For
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some types of manure, adding rice hulls, woody material or straw allows to process the manure into a high
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quality compost [22]. C-rich materials can be mixed at the onset of composting, or can be added already as
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bedding material in the stable. The bedding material may affect the compost quality, as shown by Larney et
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al. [5] for wood chip-bedded and straw-bedded cattle manure. Studies differ in the amount of poultry manure
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applied in the composting process, the maturity of the composts and the composting system. Higher ratio of
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poultry manure in the feedstock mixture of composting resulted in higher extractable P [3]. Compost quality
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is affected by its stability. The biodegradation potential of organic matter may be used as an indicator of
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compost stability and can be expressed by several indices based on the cell wall components lignin,
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hemicellulose and/or cellulose [23-28]. Based on the biochemical composition, Gabrielle et al. [23]
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calculated a biological stability index to predict C and N mineralisation in compost. Francou et al. [24] and
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Lashermes et al. [25] applied the lignin/holocellulose ratio as an indicator during the composting process.
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Paradelo et al. [26] reported that the fractionation of organic matter into cellulose, hemicellulose and lignin
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enabled a better monitoring of the waste decomposition. Chalhoub et al. [28] reported that the compost with
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the highest (hemicellulose + cellulose)/lignin ratio, i.e., the highest biodegradation potential also resulted in
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the highest amount of potentially mineralized C in an incubation trial, indicating it was the least mature
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compost.
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Mixing biochar in compost may affect both the compost quality and the biochar characteristics. Borchard et
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al. [29] concluded that composting increases the surface reactivity of biochars, potentially enhancing nutrient
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retention in soils. Applying 2 vol% of biochar (made from wood) in the feedstock of chicken manure
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composting resulted in a compost with better chemical and biochemical characteristics in terms of
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stabilization indices, the microbial biomass and enzymatic activities related to the C, N and P cycles [7].
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Dias et al. [6] mixed chicken manure with biochar (made from wood), coffee husk or sawdust in a 1:1 fresh
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weight ratio at the beginning of the process. The biochar proved to be a good bulking agent, resulting in
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intensive humification and reduced N losses in the mature compost.
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This research was set up to determine the effect of feedstock composition on P content and availability in
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chicken manure compost and in products from other valorisation strategies for chicken manure. Specific
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research questions are: 1) are chicken manure-based composts good soil improvers (compared to alternative
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processing), 2) what are the Cd, Zn and Mn concentrations in these products, 3) what is the amount of
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chicken manure that can be added to the compost in order to obtain quality compost in terms of product
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stability, 4) what is the effect of composting on P-availability, 5) can addition of biochar further improve
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compost quality? To assess the effect of biochar on compost properties, one of the composts based on
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chicken manure was mixed with biochar with a higher C/P ratio than the compost.
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2 METHODOLOGY
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2.1 Compost trials and other applications of chicken manure
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Composts based on chicken manure (two trials) are compared with other treatment options for chicken
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manure: mixed storage of chicken manure and green waste, manure treatment in a central processing facility,
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and application of green waste compost as bedding material in chicken houses (Table 1). All treatments have
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in common that the chicken manure was ‘mixed’ in one way or another with materials with higher C/P ratios
99
and C/N ratios. In all treatments except the use of green waste compost in chicken houses, the chicken
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manure was mixed at the onset of the experiment. By mixing the manure with more stable materials, we
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aimed at reducing N leaching losses and gaseous losses, and producing a value-added organic fertilizer, i.e.,
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a product with optimal properties for the end user.
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COMPOST TRIAL 1
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In the first compost trial (Table 2), three alternative feedstock mixtures were compared for composting with
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fresh chicken manure. The mixture of each of the three treatments consisted of chicken manure, wheat straw
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and fresh grass clippings. These feedstock materials were completed with a mixture of grass hay and green
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waste compost for compost A, tree bark for compost B and grass hay for compost C (Table 2). Feedstock
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mixtures had a C/N content of 30/1, which is generally considered an ideal starting ratio for composting. The
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mixtures were composted in open air on a site with concrete floor at the experimental farm of ILVO in
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Merelbeke, in a windrow system with a length of 20m per compost type. The individual feedstock materials
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used in the composting process (Table 3) and the feedstock mixtures were sampled at the start in four
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replicates (each based on 10 subsamples) and samples were stored in the refrigerator at 4°C. Some feedstock
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mixtures contain very dry and light materials such as straw and hay (Table 3, Table 4). This is the
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explanation for the clear differences in composition on DM% base (Table 1) or on vol% base (Table 2).
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On September 22nd 2010, the three compost piles were set up by arranging the feedstock materials in a
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windrow with the least dense material (wheat straw and grass hay) below and the most dense material
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(chicken manure) on top, so as to obtain an ideal, homogeneous mixture after turning with a Tractor-pulled
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Sandberger ST300 windrow compost turner. Temperature and CO2 levels in the composts were monitored to
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detect the need for compost turning. The composts were mechanically mixed when too high temperatures (>
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65°C) or CO2 levels (> 16 vol% CO2) were measured. When the feedstock mixture became too dry water
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was added to the compost with a drip irrigation system of the “Uniram” type, at an hourly rate of 8 litre
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water per meter windrow. The windrows were covered with semipermeable fabrics to avoid too high water
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contents. The need for turning the compost was highest shortly after starting the composting, with
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temperature peaks over 65°C (Fig. 1). Especially mixture B was highly reactive, and needed to be turned 11
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times during the trial. Mixture A and C were turned 6 and 10 times, respectively. CO 2 levels were higher for
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compost A and C than for compost B, especially during the first week (results not shown). Maximum values
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were 12 to 14% CO2. Compost B needed most additional water, which was supplied during five full days.
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Compost A and C were supplied with water during one and three days, respectively. After 10 weeks of
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composting, compost A and C were stored in two piles as the temperature was already below 30°C. These
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piles and the windrow for compost B were sampled on January 5th 2011, 15 weeks after the composting
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process started. Four samples per row or pile (each based on 10 subsamples) were taken and sieved over a 20
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mm mesh and stored in the refrigerator at 4°C. The separate feedstock materials (Table 3) and composts
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were weighed on a weigh bridge when compost piles were set up and at time of sampling.
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COMPOST TRIAL 2
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In the second trial, the effect of the amount of chicken manure in the feedstock mixture was assessed, i.e. 10,
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17 or 20 vol% (Table 2), but with the same methodology as in the first trial. The tested feedstock materials
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were wheat straw, grass clippings, poplar bark, willow wood chips, and grass hay (Table 4). The wood chips
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were harvested in a plot with Salix viminalis in the short rotation coppice plantation of ILVO. The
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composting started on February 18th 2011. Due to dry weather conditions, intensive follow-up of the process
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(e.g. regular moistening) was necessary. The second composting experiment was characterized by high
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temperatures over a long period, indicating that the applied feedstock mixture served as a long-term C source
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for the process (Fig. 2). Irrespective of the continuously high temperatures and activity, the three composts
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were weighed, sampled and stockpiled on 15th of May 2011.
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Besides the second compost trial, a 50:50 dry matter ratio mixture of green waste compost and fresh chicken
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manure was stockpiled during the same period (February 18th until May 9th) and sampled after 3 and 7
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months. Temperature increased within the stockpiled mixture of chicken manure and green waste compost,
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but never exceeded the temperatures measured in the compost windrows (Fig. 2). At time of sampling, four
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samples per windrow or pile (each based on 10 subsamples) were taken and sieved over a 20 mm mesh and
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stored in the refrigerator at 4°C.
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OTHER TREATMENTS WITH CHICKEN MANURE
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We furthermore tested the effect of two other treatments of chicken manure on the chemical properties of the
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end product. A fresh weight mixture of 73.5% chicken manure + 21% green waste compost + 5.5% horse
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manure was processed for hygienisation (10 hours >70°C) at a central manure processing facility (Compofert
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Plant Kallo (Belgium), Op de Beeck Group) with active tunnel aeration (7 days), followed by storage (closed
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system, NH3 recirculation with NH3 stripping). The processed material was sampled directly after the active
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tunnel aeration: four samples (each based on 10 subsamples) were taken from the pile and sieved over a 20
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mm mesh and stored in the refrigerator at 4°C.
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A 30 cm layer of green waste compost was used as bedding material in a chicken house with 3000 laying
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hens during 5.5 months. The compost was applied on a surface of 26 x 3.6m, this was half of the stable area.
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The compost bedding material was wetted regularly with an irrigation system, and homogenized with a
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cultivator. After four months low amounts of chipped straw were added as C source at a rate of ± 200 kg FW
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/ month. The bedding material in the chicken house was sampled after 2 and 5.5 months. At each sampling
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event, four samples were taken, each composed of 10 subsamples, sieved over a 20 mm mesh and stored in
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the refrigerator at 4°C. Analysis methods are listed in Table 5.
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2.2 Effect of mixing biochar in compost based on chicken manure
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Compost E was sampled on July 3th 2012 (after 13 months of storage). the fraction < 8mm was mixed with
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10% biochar on a fresh weight base in four replicates. The biochar (fraction < 2 mm) was provided by
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Proininso Inc. (Málaga, Spain), for which holm oak was used as feedstock for pyrolysis at 650°C. The
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mixtures were stored during five days at 20°C and then sampled for analysis. Analysis methods are listed in
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Table 5.
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2.3 Data processing and statistics
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Twelve compost products were sampled in this study: three chicken manure compost products in each of
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both compost trials, the bedding compost sampled after 2 and 5.5 months, the centrally processed chicken
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manure, the green waste compost used in the experiment with the stockpiled compost/chicken manure
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mixture, and the stockpiled green waste compost/chicken manure mixture sampled after 3 and 7 months. For
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these products, the relationship between total and NH4 acetate extractable P and other compost
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characteristics were investigated by correlation analysis of the average of the four measurements per product
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and per sampling event. Based on the fractions determined according to Van Soest et al. [30], the
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biodegradation
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%cellulose)/%lignin.
potential
was
calculated
as
the
holocellulose/lignin
ratio:
(%hemicellulose
+
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3 RESULTS & DISCUSSION
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3.1
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Products were assessed for their value as soil improver and organic fertilizer. A high organic matter content
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combined with a high C/P ratio is beneficial for the product quality. Mineral N is preferentially in nitrate
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form, as it indicates aerobic conditions in the product. Low OUR (oxygen uptake rate) values are typical for
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stable products [31]; a high stability in combination with a high portion NO3-N in the mineral N pool
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indicates that no N immobilization in the soil will occur at time of field application. High EC values indicate
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high salt contents, which may limit plant growth when compost is mixed with soil. Based on these chemical
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characteristics, the chicken manure compost with 42.5 vol% bark in the feedstock (compost B) had the
Quality as soil improver and organic fertilizer
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highest quality as soil improver, i.e. the highest OM content (on DM base), lowest EC, lowest OUR and
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highest C/N and C/P ratio (Table 6, Table 7).
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The highest stability is found for chicken manure compost E: it has the lowest OUR value and the highest
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NO3 concentration. Compost D has a higher OM content and a higher N/P and C/P ratio than compost E and
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F (Table 6). These results indicate that 10 vol% of fresh chicken manure is the upper limit in small-scale on-
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farm windrow composting above which nutrient losses become too high and the N/P ratio of the obtained
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fertilizer becomes too low (Table 6). The stockpiled mixture was characterised by high NH4-N
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concentrations and high OUR values after 3 months of storage, indicating the instable nature of the mixture
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(Table 7).
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The C/P ratio was low for the stockpiled mixture of green waste compost and chicken manure. For this
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product, a low C/P ratio and the low OM content indicate that the mixed storage of high doses of chicken
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manure with green waste compost is not a good way for processing chicken manure. It might be a better
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option to mix green waste compost and chicken manure just before application in the field, as mixed storage
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of high doses of chicken manure resulted in high mass and nutrient losses in this study.
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After 5.5 months, the bedding material was rich in mineral N, had a favorably high C/P ratio (even higher
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than for the composts based on chicken manure) but both the OUR and the NH4-N/NO3-N ratio indicate that
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the product is not fully stable yet (Table 7). As fresh chicken manure is added during the whole period to the
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bedding material, stabilization in the chicken house will be a slow process. The high C/P ratio for the
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compost-bedded chicken manure illustrates the positive effect of the applied compost. In future research it
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should be tested if this product can be further stabilized by composting after removal from the chicken
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houses, as was reported by Larney et al. [5] for beef cattle feedlot manure. Storage of the bedding material
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after removal may result in high N losses, as shown above for the storage of the green waste compost and
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chicken manure mixture.
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Chicken manure compost B, D, the processed chicken manure and the bedding material were characterized
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by higher C/P ratios and higher OM contents (Table 7), making them suitable products for application in the
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field. Due to this higher C/P ratio, these products can be applied in a higher dose than fresh chicken manure
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without exceeding the fertilization standards [1-3]. The latter two products still had high NH4-N
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concentrations, which may result in N losses during application. As the compost used as bedding material
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initially was characterized by a C/P ratio > 100, the resulting product had the highest C/P ratio of the
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products tested in this study (Table 7). Two of the 12 products were characterised by high NH4-N
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concentrations, high OUR values and high NH4-N/NO3-N ratios (Table 7), indicative for the not fully mature
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state of these products: the stockpiled mixture of poultry manure and green waste compost after 3 months
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storage, and the centrally processed manure. The stockpiled manure was still not mature after 7 months of
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storage, as illustrated by the OUR determination (Table 7). Feedstock selection is a means to create value-
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added compost, as was reported previously by Tognetti et al. [21] and Leconte et al. [22]. Based on the
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temperature progress during the processing, only the composts A to E and the centrally processed manure
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had a sufficient degree of hygienisation. The temperatures >60°C in these products may result in faster or
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stronger degradation of undesired substances such as veterinary drugs [17-18], reducing the risk of plant
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uptake in case of field application of chicken manure [13-16].
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Chicken manure is rich in K, Ca and Mg in relation to the other feedstock materials (Table 3, Table 4). Grass
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hay and grass clippings may also have high K concentrations (Table 3, Table 4). The lower the amount of
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chicken manure in the feedstock mixture and the lower the mass reduction during the compost process, the
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lower are the K, Ca and Mg concentrations in the composts. This is illustrated by the lower K, Ca and Mg
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concentrations in compost B versus compost A and C (due to lower mass reduction), and in compost D
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versus compost E and F (lower amount of chicken manure in the feedstock mixture) (Table 6).
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3.2
Cd, Zn and Mn concentrations
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High heavy metal concentrations may reduce the quality of the chicken manure-based products in terms of
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applicability as soil improver or organic fertilizer. Concentrations of Cd, Zn and Mn in the compost are
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affected both by concentrations in the feedstock mixture and by the mass reduction during composting. In the
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first compost trial, Cd concentrations were relatively high in the poplar bark (Table 3), leading to higher
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concentrations in compost B than for compost A and C. In the second compost trial, Cd concentrations were
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high in the poplar bark and the wood chips (Table 4), leading to high Cd concentrations in all composts
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(Table 6). The wood chips were harvested from a plot with Salix viminalis in the short rotation coppice
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plantation of ILVO, and higher Cd concentrations for this species were observed previously in bark and
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wood compared to other species [32]. Higher Cd concentrations in the compost due to the use of bark or
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wood chips did not result in higher risk of Cd leaching [32]. Zn and Mn concentrations were high in the
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chicken manure, especially in the second compost trial (Table 3, Table 4). The Cd concentrations in the
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composts exceed the legal criterion of 2 mg Cd/ kg DM compost in compost D, E and F, while the legal
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criterion of 400 mg Zn/ kg DM compost is exceeded for compost E and F (Table 6). Legal criteria for Mn
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concentrations in compost do not currently exist. Increasing the amount of wood chips or bark in the
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feedstock mixture allowed to increase the quality of the composts in terms of C/P ratio and OM (Table 7),
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but this also resulted in higher Cd and Zn concentrations (Table 6), thus reducing the quality in terms of
256
heavy metal concentrations.
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3.3
Mass reduction, biodegradation potential and product stability
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The feedstock mixture of compost B had a lower biodegradation potential, which is reflected in a lower mass
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reduction than for the other two composts (Table 8). After composting, a lower biodegradation potential was
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measured for compost B than for compost A and C (Table 8).
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The mass reduction for the three composts of trial 2 was clearly higher than for those of trial 1, while a low
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mass reduction was observed for the stockpiled manure (Table 8). The second composting experiment was
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characterized by high temperatures over a long period (Fig. 2), indicating that the applied feedstock mixture
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served as a long-term C source for the process.
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The feedstock mixtures of the three windrows in the second composting experiment and the feedstock
267
mixture for the stockpile experiment had a comparable biodegradation potential (Table 8). The
268
biodegradation potential for the feedstock mixtures in the second composting experiment were clearly lower
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than for feedstock mixture of compost A and C. This indicates that the biodegradability of chicken manure
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and grass clippings were similar. After three months of storage, the stockpiled mixture of green waste
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compost and chicken manure had a higher biodegradation potential than the composts based on chicken
272
manure (Table 8), and after 7 months the biodegradation potential was still higher than for chicken manure
273
compost B, D, E and F (Table 8).
274
The biodegradation potential was found to be a useful indicator for comparing feedstock mixtures and end
275
products. Within compost trial 1, mass reduction during composting was related to biodegradation potential
276
of the feedstock mixture (Table 8). Blanco & Almendros [27] reported a clear decrease in holocellulose
10
277
content and an increase in the lignin content during composting of urea-amended wheat straw with 5% dry
278
weight horse manure. During this process, the holocellulose/lignin ratio decreased from 5.0 to 1.6 [27]. We
279
found a similar decrease in our compost trials (Table 8). A good positive correlation was found between
280
OUR (Table 7) and the biodegradation potential (Table 8) for the samples of the two compost trials and the
281
green waste compost and the end product of the storage trial (R2 = 0.76, n = 8, p < 0.01). Our results confirm
282
that the biodegradation potential is a useful indicator in monitoring decomposition processes during
283
composting and storage as reported previously [23-28].
284
285
3.4
Total and available P
286
Chicken manure was the main source of P in compost trial 1 and 2. For compost trial 1, chicken manure
287
accounted for 72, 79 and 75% of the P in the feedstock mixture for compost A, B en C, respectively. In
288
compost trial 2, 83, 90 and 92% of the P originated from the manure for compost D, E and F, respectively.
289
The amount of P supplied by chicken manure in the stockpiled mixture of chicken manure and green waste
290
compost was 86% of the total amount of P. Total P concentrations were higher in the chicken manure
291
composts than in the initial feedstock mixtures (Fig. 3) due to the mass reduction during composting [12].
292
0.25M NaOH-extractable P concentrations were higher in the chicken manure composts than in the initial
293
feedstock mixtures (Fig. 3), but the 0.25M NaOH-extractable P concentrations were relatively lower for the
294
chicken manure composts than for the feedstock mixtures (Fig. 3), pointing at P stabilisation during
295
composting, as was observed previously by Felton et al. [12] based on a decrease in water-soluble P during
296
the process.
297
NH4-acetate, CaCl2/DTPA and 0.25M NaOH-extractable P concentrations were lower for compost B than for
298
the other two chicken manure composts (Fig. 3). The lower P availability is related to the lower P content
299
due to the lower mass reduction for compost B, as illustrated by the lower biodegradation potential for
300
compost B than for compost A and C (Table 8).
301
NH4-acetate and CaCl2/DTPA -extractable P concentrations were lower in the composts D, E and F than in
302
the stockpiled mixture of chicken manure and green waste compost (Fig. 3), pointing at a stabilisation of P in
303
the composting process. With exception of the samples of the stockpiled mixture with poultry manure, a
304
positive relationship between total and NH4-Acetate extractable P was observed (Fig. 4). For the stockpiled
11
305
chicken manure after three months of storage and the centrally processed manure, both the high OUR and the
306
high NH4-N/NO3-N ratio point at an incomplete composting and partly anaerobic circumstances (Table 5). In
307
partly anaerobic conditions NO3-N can be transformed to NH4-N due to redox reactions. After 7 months of
308
storage, the OUR value was lower, indicating a higher stability of the mixture, but NO3-N concentrations
309
were still small, especially in comparison with the high NH4-N concentrations in the mixtures (Table 7).
310
311
Inorganic P was found to be the most important form of P in a range of composts and other biosolids [33-34].
312
Inorganic P can be both apatite inorganic P (form associated with Ca) and non-apatite inorganic P (forms
313
associated with oxides and hydroxides of Al, Fe and Mn). For the feedstock materials used to produce the 12
314
compost products, no clear relationship between total Ca and P concentration was observed. Regarding the
315
Ca/P ratio in the feedstock materials, three groups could be distinguished: tree bark with an average Ca/P
316
ratio of 25.6 and an average content of 26.0 g Ca/kg DM, poultry manure with an average Ca/P ratio of 4.2
317
and an average content of 82.0g Ca/kg DM, and the other feedstock materials with an average Ca/P ratio of
318
2.8 and average content of 4.9g Ca/kg DM. In contrast to the feedstock materials, a clear positive
319
relationship between total Ca and P was detected in the compost products, with exception of the centrally
320
processed manure. For the other 11 products, a positive correlation (R2 = 0.92, p < 0.001) between both
321
parameters was found. The pHH2O of the 12 products ranged between 7.68 (green waste compost used in the
322
storage trial) and 8.75. We also observed a strong positive correlation (R2 = 0.81 (p < 0.001, n=12) and 0.96
323
(p < 0.001, n=11) with and without the centrally processed manure, respectively) between NH4-Acetate
324
extractable P and the NH4-Acetate extractable Ca (Fig. 4). These results indicate that P binding and
325
availability in the products after processing is related to Ca, and that apatite P is the dominant P form in the
326
studied products.
327
Although Ca concentrations in the NH4-Acetate extract were 100x higher than Fe and Mn concentrations
328
(Fig. 4), Mn and Fe can give an indication on the effect of anaerobic conditions on P availability. In general,
329
we found a clear positive relationship between NH4-Acetate extractable P and the NH4-Acetate extractable
330
Fe or Mn (Fig. 4), but the unstable products (centrally processed manure and stockpiled manure/compost
331
mixture) deviated from this linear relationship. The availability of Mn and Fe is known to increase in
332
anaerobic conditions [35], and these products also had higher OUR and a higher NH4-N/NO3-N ratio, as
12
333
discussed above. Availability of Mn and Fe increases when oxygen levels decrease due to decomposition
334
activity, and these changes affect the P availability in the products.
335
P availability in the compost will change when compost is applied to the soil. Gagnon et al. [33] reported that
336
compost application resulted in lower labile P but comparable total inorganic P than when pure KH2PO4 was
337
added to the soil. Composting of poultry litter mixed with hardwood chips or pine sawdust did not change P
338
availability in soil in comparison with fresh poultry litter [1].
339
3.5
340
As the applied biochar had a higher C/P ratio than the chicken manure compost (Table 9), blending the
341
compost with biochar resulted in a product with a higher C/P ratio, a higher OM content and a lower P
342
content (Table 7). The main effect was a more than proportional decrease in easily available P in the biochar-
343
blended compost, both as water extractable and CaCl2/DTPA extractable P (Table 9).
344
P in the biochar-blended compost can be bound by Ca, or by Fe, Al and Mn. Total Ca content in the biochar
345
(65g/kg DM) is clearly higher than the total Al (<0.1g/kg DM), Fe (0.3g/kg DM) and Mn (0.4g/kg DM)
346
content. As pHH20 and NH4-acetate extractable Ca are increasing by biochar amendment while NH4-acetate
347
extractable Fe and Mn are decreasing (Table 9), this indicates that the easily available P in the chicken
348
manure compost is bound by Ca when blending the compost with biochar.
349
Addition of biochar is an option to increase C/P ratio and OM content while reducing the leaching risk of P
350
from compost: amending biochar resulted in lower easily available P concentrations, thus reducing the water-
351
extractable P prone to leaching [11]. As biochar is mainly organic matter, blending compost with biochar
352
may not result in long-term fixation of P in the compost-amended soil. Application of other immobilizing
353
agents (e.g. gypsum [9], Al- and Fe-rich materials [10]) may lead to irreversible or long-term P
354
immobilization. More research on effects of biochar type and/or dose is necessary to further elucidate this
355
potential application. The effect of biochar on P availability in compost might also be affected by the
356
moment of biochar application, i.e. at the start of the composting process [6, 7] or in the mature compost.
Effect of mixing biochar in compost based on chicken manure
357
13
358
4
CONCLUSIONS
359
Several valorisation strategies for chicken manure were tested on their value as soil improver. Total P
360
concentration in the chicken manure compost was found to be the result of P in the feedstock mixture and
361
mass reduction during composting, which is driven by the biodegradation potential of the feedstock. The
362
latter is found to be a useful method for screening the value of feedstock mixtures for composting. Results
363
point at a stabilisation of P during the composting process. In order to reduce nutrient losses and achieve a
364
fertilizer with a sufficiently high C/P ratio, we conclude that for small-scale on-farm windrow composting of
365
chicken manure a sufficient amount of wood chips or bark should be combined with a maximum of 10 vol%
366
of fresh chicken manure. Changing the feedstock composition in the composting process allowed to increase
367
the value of chicken manure as soil improver.
368
The results indicate that apatite P is the dominant P form in the studied products and that P binding and
369
availability after processing is related to Ca. P availability was affected by stability and redox circumstances
370
in the chicken manure products. P availability increased in case of anoxic conditions in the product. The
371
mixed storage of high doses of chicken manure and green waste compost seemed not to be efficient. The end
372
products of applying green waste compost as bedding material and of the central processed manure had a
373
high C/P ratio and a high OM content, making them suitable as soil improver and organic fertilizer. The
374
results indicate a high potential for using green waste compost as bedding material in chicken houses. Wood-
375
based biochar was found to be a potential solution to increase the C/P ratio and reduce the amount of easily
376
available P in chicken manure compost. This should be further tested.
377
378
5
ACKNOWLEDGEMENTS
379
We wish to thank the lab and field technicians of ILVO for their help during the composting trials, and for
380
executing the chemical analyses. This research was partly financially supported by the Flemish Government
381
- Sustainable Agricultural Development Division (ADLO), and partly executed within the FERTIPLUS
382
project. The project FERTIPLUS (Grant Agreement N° 289853) is co-funded by the European Commission,
383
Directorate General for Research & Innovation, within the 7th Framework Programme of RTD, Theme 2 –
384
Biotechnologies, Agriculture & Food. The views and opinions expressed in this paper are purely those of the
14
385
writers and may not in any circumstances be regarded as stating an official position of the European
386
Commission. We are grateful to Jos Arits and the Op de Beeck group for their logistic support, and to
387
Antonio Quero Alba from PROININSO S.A. for providing the biochar based on holm oak.
388
15
389
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390
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of lignocellulosic winery wastes. J. Environ. Manage. 116, 18-26 (2013).
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progressive composting stages of wheat straw. Plant Soil 196, 15-25 (1997)
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[29] Borchard, N., Prost, K., Kautz, T., Moeller, A., Siemens, J.: Sorption of copper (II) and sulphate to
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different biochars before and after composting with farmyard manure. Eur. J. Soil Sci. 63, 399- 409 (2012)
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Nonstarch Polysaccharides in Relation to Animal Nutrition. J. Dairy Sci. 74, 3583-3597 (1991)
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determination of the intrinsic carbon and nitrogen mineralization capacity of natural organic matter
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sources. Soil Biol. Biochem., 39, 1493-1503 (2007)
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[32] Vandecasteele, B., Willekens, K., Zwertvaegher, A., Degrande, L., Tack, F.M.G., Du Laing, G.: Effect
465
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466
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[33] Gagnon, B., Demers, I., Ziadi, N., Chantigny, M. H., Parent, L.-E., Forge, T. A., Larney, F. J., Buckley,
468
K. E.: Forms of phosphorus in composts and in compost-amended soils following incubation. Can. J. Soil
469
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470
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471
Characterisation and environmental risk. Waste Manage. 32, 1061-1068 (2012)
18
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[35] Du Laing, G., Bontinck, A., Samson, R., Vandecasteele, B., Vanthuyne, D.R.J., Meers, E., Lesage, E.,
473
Tack, F.M.G., Verloo, M.G.: Effect of decomposing litter on the mobility and availability of metals in the
474
soil of a recently created floodplain. Geoderma 147, 34-46 (2008)
475
19
476
477
478
479
FIGURE 1
Temperature evolution during composting for the three composts (A: circles, B: squares, C: triangles) in
compost trial 1.
480
20
481
482
483
484
FIGURE 2
Temperature evolution during composting for the three composts (D: circles, E: squares, F: triangles) in
compost trial 2, and the stockpiled mixture of compost and chicken manure (S: crosses).
485
21
486
487
FIGURE 3
P concentrations in 4 extracts for feedstock mixtures (FM) and composts of the three composts (A-B-C) in
488
compost trial 1, the three composts (D-E-F) in trial 2, and the stockpiled mixture of compost and chicken
489
manure after 3 months of storage (S). Data are average values of 4 separately analysed samples.
490
22
491
492
493
FIGURE 4
Relationship between NH4-Acetate extractable P concentrations in 12 products based on chicken manure,
494
and total P concentrations or NH4-Acetate extractable Fe and Mn concentrations. S3 and S7: stockpiled
495
mixture of compost and chicken manure sampled after 3 and 7 months, respectively, CP: centrally
496
processed chicken manure, AC: acetate. Each point is the average of 4 analysed samples per product.
497
23
498
499
TABLE 1
Details on the experimental set-up of trials on chicken manure processing: feedstock materials, samplings,
502
Treatment
Initial material
Mass reduction and degree of biodegradation
compost).
% Chicken manure in initial mixture (DM base)
501
End product sampled after # days
amount of chicken manure in the initial mixture and analyses (DM: dry matter, GW compost: green waste
Intermediate sampling after # days
500
chicken manure compost A
Chicken manure, wheat straw, grass clippings, grass hay, GW compost
no
97
19
x
chicken manure compost B
Chicken manure, wheat straw, grass clippings, poplar bark
no
97
22
x
chicken manure compost C
Chicken manure, wheat straw, grass clippings, grass hay
no
97
28
x
chicken manure compost D
Chicken manure, wheat straw, grass clippings, grass hay, poplar bark, wood chips
no
81
30
x
chicken manure compost E
Chicken manure, wheat straw, grass clippings, grass hay, poplar bark, wood chips
no
81
42
x
chicken manure compost F
Chicken manure, wheat straw, grass clippings, grass hay, poplar bark, wood chips
no
81
47
x
x
Storage
Chicken manure, GW compost
80
222
47
Central processing
green waste compost, horse manure, chicken manure
no
7
79
Bedding material
green waste compost
72
174
0
503
504
24
505
506
507
TABLE 2
Feedstock composition (vol%) of the three composts (A-B-C) in trial 1 and the three composts (D-E-F) in
trial 2
Compost
trial
Compost
1
A
B
C
2
D
E
F
Chicken
manure
10%
7.5%
7.5%
10%
17%
20%
wheat
straw
30%
30%
30%
15%
12%
13%
grass
clippings
15%
20%
20%
21%
17%
13%
poplar
bark
42.5%
27%
27%
27%
wood
chips
18%
18%
18%
grass hay
compost
25%
42.5%
9%
9%
9%
20%
-
508
509
25
510
511
TABLE 3
Chemical properties of the feedstock materials used in compost trial 1 (OM: organic matter, DM: dry
matter, Ntot: total nitrogen). Values are averages ± standard deviation of 4 samples per feedstock
512
Variable
grass hay C
grass hay A
Chicken
grass
manure
clippings
poplar bark
OM (%/DM)
95.1 ± 0.3
92.4 ± 0.5
91.2 ± 2.7
90.3 ± 0.5
42.8 ± 1.9
88.2 ± 0.6
DM (%)
36.8 ± 3.4
63.5 ± 5.8
16.8 ± 3.3
46.5 ± 1.9
62.7 ± 0.6
8.9 ± 0.7
73 ± 0
27 ± 0
55 ± 0
205 ± 2
533 ± 20
80 ± 0
Cd (mg/kg DM)
0.15 ± 0.02
0.11 ± 0.02
0.17 ± 0.05
1.72 ± 0.18
0.31 ± 0.01
0.12 ± 0.01
Zn (mg/kg DM)
26 ± 9
40 ± 2
64 ± 10
222 ± 8
244 ± 209
70 ± 29
Mn (mg/kg DM)
15 ± 1
117 ± 12
125 ± 54
62 ± 9
225 ± 135
77 ± 2
C/N (-)
117 ± 7
51 ± 3
34 ± 11
58 ± 8
8.25 ± 0.75
24 ± 1
N/P (-)
7.61 ± 0.7
5.13 ± 0.84
5.93 ± 0.4
7.07 ± 0.65
1.94 ± 0.56
4.94 ± 0.08
C/P (-)
901 ± 128
264 ± 31
203 ± 67
410 ± 59
15.87 ± 3.28
120 ± 4
Ntot (g/kg DM)
4.52 ± 0.26
10.00 ± 0.60
16.02 ± 4.90
8.80 ± 1.07
29.03 ± 3.52
20.28 ± 0.53
P (g/kg DM)
0.60 ± 0.09
1.98 ± 0.22
2.70 ± 0.74
1.25 ± 0.17
15.51 ± 2.59
4.10 ± 0.12
K (g/kg DM)
2.6 ± 0.1
17.6 ± 1.7
11.9 ± 3.5
6.6 ± 0.3
21.7 ± 0.4
35.4 ± 0.8
Ca (g/kg DM)
2.9 ± 0.3
4 ± 0.3
6.5 ± 1.2
26.6 ± 1.4
73.9 ± 3.4
4.8 ± 0.3
Mg (g/kg DM)
0.70 ± 0.01
1.17 ± 0.11
1.50 ± 0.28
1.74 ± 0.23
4.86 ± 0.03
1.71 ± 0.05
bulk density (g/l)
513
wheat straw
514
515
26
516
517
TABLE 4
Chemical properties of the feedstock materials used in compost trial 2 and the stockpiled mixture of
518
chicken manure and green waste compost (OM: organic matter, DM: dry matter, Ntot: total nitrogen, GW:
519
green waste). Values are averages ± standard deviation of 4 samples per feedstock
Variable
wheat straw
grass hay
poplar bark
wood chips
OM (%/DM)
93.9 ± 0.7
85.9 ± 3.3
87.5 ± 0.7
96.7 ± 1.8
59.1 ± 0.6
84.8 ± 3.4
22.83 ± 4.32
DM (%)
15.7 ± 1.5
25.4 ± 4.0
32.3 ± 1.5
46.9 ± 5.1
49.9 ± 1.2
15.2 ± 2.3
56.0 ± 1.6
99 ± 2
147 ± 14
335 ± 18
291 ± 12
551 ± 6
133 ± 11
624 ± 11
Cd (mg/kg DM)
0.13 ± 0.01
0.18 ± 0.04
3.91 ± 0.56
3.01 ± 0.27
0.30 ± 0.01
0.27 ± 0.04
0.58 ± 0.05
Zn (mg/kg DM)
27 ± 6
116 ± 36
190 ± 8
150 ± 10
589 ± 21
73 ± 15
146 ± 13
Mn (mg/kg DM)
24 ± 3
174 ± 18
75 ± 32
59 ± 6
469 ± 9
162 ± 56
261 ± 68
C/N (-)
82 ± 5
24 ± 4
64 ± 4
85 ± 7
9.4 ± 0.2
17 ± 1
12.88 ± 2.01
N/P (-)
9.86 ± 1.00
5.49 ± 0.46
8.94 ± 1.09
6.75 ± 0.70
2.48 ± 0.02
7.64 ± 0.43
4.76 ± 0.57
C/P (-)
818 ± 120
136 ± 28
575 ± 60
575 ± 19
23.5 ± 0.8
132 ± 4
60.88 ± 4.87
Ntot (g/kg DM)
6.38 ± 0.33
19.80 ± 2.22
7.63 ± 0.53
6.35 ± 0.61
34.88 ± 0.75
25.03 ± 3.42
9.88 ± 0.95
P (g/kg DM)
0.65 ± 0.08
3.64 ± 0.66
0.86 ± 0.08
0.94 ± 0.02
14.07 ± 0.42
3.3 ± 0.57
2.09 ± 0.22
K (g/kg DM)
2.8 ± 0.6
26.8 ± 7.5
7.0 ± 0.8
2.8 ± 0.1
24.6 ± 0.9
18.6 ± 7.5
4.0 ± 1.0
Ca (g/kg DM)
3.1 ± 0.1
10.2 ± 2.2
25.4 ± 1.8
7.5 ± 0.2
86.6 ± 4.8
4.6 ± 0.6
17.1 ± 1.5
Mg (g/kg DM)
0.87 ± 0.08
2.36 ± 0.53
1.46 ± 0.08
0.58 ± 0.01
7.31 ± 0.43
1.85 ± 0.33
3.1 ± 0.46
bulk density (g/l)
520
Chicken manure grass clippings
GW compost
27
521
522
TABLE 5
Analysed parameters, methods and references.
Parameter
Method and reference
Sample preparation
EN 13040
Dry matter (DM) content
EN 13040
Laboratory compacted bulk density
EN 13040
pH-H2O
1:5 (v/v) soil to water suspension, EN 13037
Electrical conductivity (EC)
1:5 (v/v) soil to water suspension, EN 13038
Organic matter (OM) content
EN 13039
Water extractable NO3-N
1:5 v/v extraction in water (EN 13652), Dionex DX-600 IC ion chromatograph
Water extractable NH4-N
1:5 v/v extraction in water (EN 13652), Foss Fiastar 5000 continuous flow analyser
NH4 Acetate extractable Ca, K, Mg, P, Mn, Fe
1:5 v/v extraction in NH4 acetate buffered at pH 4.65, measured by Varian VISTA-PRO ICP-OES
CaCl 2/DTPA-extractable P
1:5 (v/v) 0.01M CaCl2 + 0.002M DTPA extract (EN 13651), measured by Varian VISTA-PRO ICP-OES
Total N
Dumas Method (EN 13654-2), Thermo Flash 4000
shaking 20g fresh compost (<1cm) in 200ml buffered nutrient solution during 5 days in a closed Oxitop
Oxygen uptake rate (OUR)
respirometer (Grigatti et al. [31])
523
Total concentrations for Cd, Zn, Mn, K, Mg, Ca and P
ashing, digestion with HNO3 (p.a. 65%), measured by Varian VISTA-PRO ICP-OES
0.25 M NaOH and 0.05 M Na2-EDTA extractable P
1:20 (w:v) in 0.25 M NaOH/0.05 M Na2-EDTA, 16h shaking at 22°C, measured by Varian VISTA-PRO ICP-OES
Neutral detergent fibre (NDF) content
Ankom220 Fiber Analyzer extraction unit, Van Soest et al. [30]
Acid detergent fibre (ADF) content
Ankom220 Fiber Analyzer extraction unit, Van Soest et al. [30]
Acid detergent lignin (ADL) content
Ankom220 Fiber Analyzer extraction unit, Van Soest et al. [30]
28
524
525
TABLE 6
Chemical properties of the produced composts and the stockpiled mixture. Values are averages ±
526
standard deviation of 4 samples per product. Compost trial 1: compost A, B and C; compost trial 2:
527
compost D, E and F, S: stockpiled mixture of chicken manure and green waste compost after 3 (‘3m’) and
528
7 (‘7m’) months
Variable
A
B
C
D
E
F
S (3m)
S (7m)
pH-H2 O (-)
8.56 ± 0.14
8.59 ± 0.06
8.31 ± 0.05
8.7 ± 0.1
8.7 ± 0.1
8.6 ± 0.1
8.7 ± 0.1
8.3 ± 0.3
EC (μS/cm)
3385 ± 323
945 ± 109
2453 ± 217
801 ± 163
1404 ± 73
804 ± 151
5450 ± 227
1654 ± 605
DM (%)
37.5 ± 1.5
34.5 ± 0.6
36.0 ± 1.9
37.0 ± 0.3
42.1 ± 1.1
34.3 ± 0.5
52.5 ± 0.4
50.6 ± 0.6
bulk density (g/l)
544 ± 15
568 ± 4
553 ± 11
502 ± 5
487 ± 7
642 ± 9
528 ± 4
734 ± 32
0.72 ± 0.06
1.14 ± 0.07
0.35 ± 0.08
2.92 ± 0.17
2.44 ± 0.06
2.42 ± 0.15
0.42 ± 0.03
0.42 ± 0.02
Zn (mg/kg DM)
341 ± 7
280 ± 30
303 ± 54
372 ± 16
513 ± 31
456 ± 23
367 ± 49
393 ± 31
Mn (mg/kg DM)
489 ± 47
231 ± 10
339 ± 77
340 ± 53
426 ± 32
512 ± 89
369 ± 32
426 ± 31
19.65 ± 1.23
16.38 ± 2.75
15.90 ± 1.92
19.58 ± 0.34
22.23 ± 0.70
19.53 ± 1.17
15.48 ± 1.96
15.03 ± 0.95
11.25 ± 0.8
9.61 ± 0.55
13.46 ± 1.78
12.03 ± 0.81
10.6 ± 0.71
11.72 ± 0.91
Cd (mg/kg DM)
N (g/kg DM)
529
P (g/kg DM)
12.09 ± 1.26
7.55 ± 1.08
K (g/kg DM)
28.5 ± 2.3
11.8 ± 0.4
26 ± 6.2
16.7 ± 0.5
20.4 ± 0.7
14.2 ± 0.8
16.5 ± 1.5
11.7 ± 2.0
Ca (g/kg DM)
68.7 ± 1.1
51 ± 1.4
60.6 ± 9.5
52.9 ± 2.2
73.9 ± 5.0
73.7 ± 1.9
53.1 ± 5.9
52.7 ± 6.8
Mg (g/kg DM)
7.31 ± 0.29
4.8 ± 0.14
6.05 ± 0.23
4.94 ± 0.16
6.28 ± 0.36
5.83 ± 0.27
4.99 ± 0.29
5.22 ± 1.44
530
531
29
532
533
TABLE 7
Chemical properties of the products based on chicken manure at different stages during processing (S:
534
start, I: intermediate, E: end). Values are averages of 4 samples per compost (OM: organic matter, OUR:
535
oxygen uptake rate, “-“: not assessed).
536
Trial
Treatment
Step NO3-N
NH4-N
(mg/l compost)
Compost trial 1
Compost trial 2
storage trial
Central processing
Bedding material
537
OM
OUR
(%/DM) (mmol/kg OM/h)
C/N
N/P
C/P
(-)
(-)
(-)
Chicken manure
S
-
-
59
-
9.4
2.5
23.5
A
E
114
46
37
7
10.4
1.6
17.2
B
E
41
<5
51
4
17.7
2.2
38.4
C
E
57
15
31
11
10.9
1.4
15.4
D
E
18
<5
65
7
18.5
2.0
38.0
E
E
134
<5
59
5
14.8
1.7
24.9
F
E
43
<5
56
6
16.0
1.6
26.1
Green waste compost
S
113
<5
23
3
12.9
4.8
60.9
3 months storage
I
17
1092
28
54
10.2
1.5
14.9
7 months storage
E
<5
210
23
14
8.6
1.3
11.0
Compost
S
<5
<5
55
-
20.0
6.6
131.0
Chicken manure
S
-
-
41
-
8.6
2.0
17.6
processed manure
E
<5
1160
59
60
9.3
2.9
27.1
Compost start
S
<5
<5
-
55
20.0
6.6
131.0
grid manure
S
-
-
58
-
9.7
2.0
19.5
After 2 months
I
34
312
53
7
14.0
4.0
57.0
After 5.5 months
E
546
301
62
12
14.0
4.0
55.0
538
539
30
540
TABLE 8
Biodegradation potential (Values are averages ± standard deviation of 4 samples) and dry matter (DM)
541
mass reduction for feedstock mixtures and composts of the three composts (A-B-C) in trial 1, the three
542
composts (D-E-F) in trial 2 and the stockpiled mixture of compost and chicken manure (S). The green
543
waste compost used in the stockpiled mixture was analysed as well (GW compost: green waste compost,
544
NA: not assessed)
545
Compost trial
1
2
546
Treatment
Biodegradation potential
% DM Mass reduction
Start
End
A
5.7 ± 0.2
1.5 ± 0.1
24%
B
2.8 ± 0.4
1.2 ± 0.1
9%
C
7.3 ± 0.3
1.8 ± 0.2
21%
D
3.1 ± 0.1
1.3 ± 0.1
40%
E
3.1 ± 0.1
1.3 ± 0.1
36%
F
3.2 ± 0.1
1.3 ± 0.1
47%
GW compost (S)
1.0 ± 0.1
S (3 months)
3.3 ± 0.6
2.4 ± 0.2
10%
S (7 months)
2.4 ± 0.2
1.6 ± 0.2
NA
547
31
548
549
TABLE 9
Effect on compost characteristics of mixing biochar at a 10% fresh weight ratio in the 0-8 mm fraction of
550
mature compost based on chicken manure (Values are averages ± standard deviation of 4 samples) and
551
properties of the applied biochar. Extractant is indicated in brackets. Values in bold are significantly
552
different (p<0.01) according to the two-sided t-test.
553
554
Variable
Unit
Biochar
Compost
Biochar-blended compost
% change
Dry Matter
%/fresh
69.4
39.4 (0.3)
42.7 (0.5)
+8
Org. Matter
%/DM
76.7
47.0 (0.5)
50.2 (1.1)
+7
total N
%/DM
2.4 (0.1)
2.1 (0.1)
-12
total P
g/kg DM
16.1 (0.3)
15.0 (0.1)
-7
pH-H20
-
8.0 (0.1)
8.4 (0.1)
+6
P (CaCl 2/DTPA)
mg/l fresh compost
329 (21)
225 (11)
-32
P (H2O)
mg/l fresh compost
37.1 (1.7)
26.3 (2.4)
-29
P (NH4 Acetate)
mg/l fresh compost
1736 (173)
1592 (95)
-8
Ca (NH4 Acetate)
mg/l fresh compost
6521 (658)
7386 (433)
+13
Fe (NH4 Acetate)
mg/l fresh compost
10.3 (0.3)
7.9 (0.6)
-23
Mn (NH4 Acetate)
mg/l fresh compost
41.4 (3.9)
41.0 (2.5)
-1
NH4-N (H2O)
mg/l fresh compost
<5
<5
-
NO3-N (H2O)
mg/l fresh compost
330 (25)
296 (39)
-10
2.8
32