Phosphorus availability and soil microbial activity in a 3 year field experiment amended with digested dairy slurry
Introduction
The residues from biogas production are increasingly being used as fertilizers in crop production. It is estimated that approximately 65 hm3 biogas residues (digestate) are produced annually in Germany [1]. Most on-farm biogas installations use animal slurries with crop and fodder residues or dedicated energy crops as input substrates [2]. The anaerobic digestion process alters the composition of the input substrate, potentially affecting plant nutrition and soil properties when the digestate is applied to the field. The total nutrient contents generally remain constant during anaerobic digestion, but the organic matter contents and the C/N ratio decrease, and the mineral N (NH4–N) contents and substrate pH increase [1], [3]. In contrast, the P solubility might decrease after anaerobic digestion due to the formation of struvite (MgNH4PO4 * 6H2O) and poorly soluble hydroxylapatite compounds (Ca5(PO4)3OH) [4], [5], [6].
Many studies have investigated the N fertilizer value of the digestate. In various incubation and pot experiments the digested slurry increased the plant-available N contents in the soil, the crop N uptake and the crop yields compared with the undigested slurry [7], [8], [9], [10]. Under field conditions, the positive effect of the digested slurry on the plant N uptake often was less pronounced or occurred only during the early growth stage [11], [12], [13], [14]. So far, less is known about the P-fertilizer effect of biogas residues. Recent studies have focused more on the effect of digestate on the soil organic matter pool and soil biology. During anaerobic digestion the easily degradable organic compounds become mineralized [15], [16], [17], and it can be expected that less but more stable organic matter is returned to field with the digestate. The mineralization of organic carbon when applied as digestate was often found to be lower than that from undigested materials [7], [16], [18]. For example, the cumulative CO2 emissions were 2.5 times lower in the soils that were amended with digested maize straw than in soils that were amended with raw maize straw over a 21 day incubation period [19]. Johansen et al. [20] found that after a 9 day incubation period, the total CO2 emissions from co-digested cattle slurry were 25% less then when raw cattle slurry was applied. So far, no differences between the undigested and (co-) digested slurry treatments have been found regarding the soil organic carbon content [9], [20], [21]. However, several laboratory and pot experiments have reported a decrease in the biomass of endogeic earthworm species, microbial biomass and dehydrogenase, β-glucosidase, cellobiohydrolase and xylanase activities in soils that were fertilized with digestate compared with soils that were fertilized with undigested slurry [9], [19], [22], indicating that the organic matter in the digestate can hardly be used as carbon and energy source by soil (micro-) organisms.
The P availability in the soil is controlled by the activity of the soil microorganisms. Digestate application may thus affect the P availability in the soil and plant P nutrition directly by adding inorganic and organic P compounds but also indirectly by affecting soil microorganisms due to the supply of nutrients organic matter. Soil microorganisms produce and excrete protons, organic anions and enzymes, thereby mobilizing P from organic and inorganic compounds and increasing the plant-available P pool in the soil [23]. In addition, the bioavailable P pool in the soil could be depleted due to the incorporation of P into the microbial biomass. Because the turnover of microbial biomass in the soil is rapid, the microbial-bound P can still be regarded as labile, readily available and is protected against fixation and leaching [23], [24].
Studying the P-fertilizer effect of biogas residues is of particular importance because natural P resources will be exhausted in the short to medium term [25], [26] and the recycling of biogas residues in agriculture is an important factor to realize nutrient cycling and to save mineral fertilizers. Therefore, this study investigated the effect of anaerobic digestion on the P fertilizer value of slurries under field conditions, taking into account the impacts on soil microbial activity. We hypothesized that changes in the composition of organic fertilizers due to the biogas process affect the P and C turnover in the soil when supplied with digestate, which, in turn, affects the plant yield and plant P nutrition.
Section snippets
Study site
An on-farm experiment was established in September 2008 in close cooperation with a local dairy farm. The experimental area is located in Mecklenburg-West Pomerania at 53°42′ northern latitude and 12°53′ western longitude. The climate of the region is characterized by an average annual precipitation of 550 mm and an average annual air temperature of 8.1 °C (German National Meteorological Service, DWD [27]). The experimental area has not received any organic fertilizer since 1995. The soil type
Effect of inputS and digestS on maize growth and nutrient uptake
In the 3 year field experiment, we analyzed the effect of anaerobic digestion on the fertilizer value of slurries, focusing on the element P. The results indicate a clear effect of the fertilizer type and the experimental year on the maize yields and P and N uptake. In general, these values were higher in the inputS and digestS treatments than in the control treatments. However, significant results were only obtained in 2011, after 3 years of continuous substrate application. Here, the P and N
Plant nutrient uptake and P solubility in the soil
The maize P and N uptake was higher under the inputS and digestS treatments than under the control treatments. However, significant differences between the fertilizer treatments were found only in the third experimental year. Commonly, under practical conditions, it takes several years for new management practices to affect the yield parameters [33]. P release from the soil into the soil solution most likely contributed to the crop P nutrition, resulting in relatively high yields in the control
Conclusion
Due to anaerobic digestion, the composition and nutrient availability of the digestate changed compared to that of the input substrate. In our 3 year field trial, this change did neither affect the N and P uptake of maize nor the P availability in the soil. Therefore, residues from the anaerobic digestion of slurries represent a valuable and readily available P source for crops. However, the lower activities of soil microorganisms and P cycle-related enzymes indicated a lower C and P turnover
Acknowledgments
We thank the Landesgraduiertenförderung Mecklenburg Western-Pommerania for providing the grant and supporting this research.
References (65)
- et al.
C and N turnover of fermented residues from biogas plants in soil in the presence of three different earthworm species (Lumbricus terrestris, Aporrectodea longa, Aporrectodea caliginosa)
Soil Biol Biochem
(2008) - et al.
Impact of anaerobic digestion on organic matter quality in pig slurry
Inter Biodeter Biodegr
(2009) - et al.
Carbon dynamics and retention in soil after anaerobic digestion of dairy cattle feed and faeces
Soil Biol Biochem
(2013) - et al.
Decomposition of biogas residues in soil and their effects on microbial growth kinetics and enzyme activities
Biomass Bioenerg
(2012) - et al.
Effects of digestate from anaerobically digested cattle slurry and plant materials on soil microbial community and emission of CO2 and N2O
Appl Soil Ecol
(2013) - et al.
Seasonal changes in soil phosphorus and associated microbial properties under adjacent grassland and forest in New Zealand
For Ecol Manag
(2003) - et al.
Soil organic matter and biological properties after 26 years of maize-wheat-cowpea cropping as affected by manure and fertilization in a Cambisol in a semiarid region of India
Agric Ecosyst Environ
(2001) - et al.
Microbial activity in a sandy arable soil is governed by the fertilization regime
Eur J Soil Biol
(2004) - et al.
Influence of various forms of green manure amendment on soil microbial community composition, enzyme activity and nutrient levels in leek
Appl Soil Ecol
(2007) - et al.
Organic amendments with reduced chemical fertilizer promote soil microbial development and nutrient availability in a subtropical paddy field: the influence of quantity, type and application time of organic amendments
Appl Soil Ecol
(2009)
Phosphorus availability to maize as influenced by organic manures and fertilizer P associated phosphatase activity in soils
Bioresour Technol
Microbial biomass content and enzymatic activities after the application of organic amendments to a horticultural soil
Bioresour Technol
CO2 emission in an intensively cultivated loam as affected by long-term application of organic manure and nitrogen fertilizer
Soil Biol Biochem
Soil respiration and human effects on global grasslands
Glob Planet Change
Sources of CO2 efflux from soil and review of partitioning methods
Soil Biol Biochem
The influence of precipitation pulses on soil respiration – assessing the “Birch effect” by stable carbon isotopes
Soil Biol Biochem
Effects of anaerobic digestion on digestate nutrient availability and crop growth: a review
Eng Life Sci
Biogasmessprogramm II
Closing the global energy and nutrient cycles through application of biogas residues to agricultural land
Energies
Fertilizer recovery from anaerobic digesters
Trans ASAE
Fertilizer value of anaerobically co-digested dairy manure and food processing wastes
Determination of phosphorus speciation in dairy manure using XRD and XANES spectroscopy
J Environ Qual
Eigenschaften und düngerwirkung von ausgefaulter gülle aus der biogasgewinnung
Arch Acker- Pflanzenbau Bodenkd
Co-digestion of animal slurry can increase short-term nitrogen recovery by crops
J Environ Qual
Anaerobically digested dairy manure as fertilizer for Maize in acid and alkaline soils
Comm Soil Sci Plant Anal
Use of anaerobically digested swine manure as a nitrogen source in corn production
Agron J
Yield and nutrient export of grain corn fertilized with raw and treated liquid swine manure
Agron J
Effects of different manuring systems with and without biogas digestion on nitrogen cycle and crop yield in mixed organic dairy farming systems
Nutri Cycl Agroecosyst
Effects of application technique and anaerobic digestion on gaseous nitrogen loss from animal slurry applied to ryegrass (Lolium perenne)
J Agric Sci
Fractionation of organic substances during anaerobic digestion of farm wastes for biogas generation
World J Microbiol Biotechnol
What is the digestate?
Wirkung von biogasrückständen auf ausgewählte bodenparameter am standort pfahlheim
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