The Maturity and CH4, N2O,NH3 Emissions from Vermicomposting with Agricultural Waste

This study investigated the maturity and gaseous emissions from vermicomposing with agricultural waste. A vermicomposting treatment (inoculated Eisenia fetida) was conducted over a 50-day period, taking tomato stems as the processing object and using cow dung as the nutrient substrate. A thermophilic composting treatment without earthworm inoculation was operated as a control treatment. During the experiment, maturity indexes such as temperature, pH, C/N ratio, and germination index (GI) were determined and continuous measurements of earthworm biomass and CH₄, N₂O, and NH₃ emissions were carried out. The results showed that the temperature during vermicomposting was suitable for earthworm survival, and the earthworm biomass increased from 10.0 to 63.1 kg m^?3. Vermicomposting took less time on average to reach the compost maturity standard (GI 80%), and reached a higher GI (132%) in the compost product compared with the thermophilic composting treatment. Moreover, the decrease of the C/N ratio in vermicompost indicated stabilization of the waste. The activities of earthworms played a positive role in reducing gaseous emissions in vermicompost, resulting in less emissions of NH₃ (12.3% NH₃-N of initial nitrogen) and total greenhouse gases (8.1 kg CO₂-eq/t DM) than those from thermophilic compost (24.9% NH₃-N of initial nitrogen, 22.8 kg CO₂-eq/t DM). Therefore, it can be concluded that vermicomposting can shorten the period required to reach compost maturity, can obtain better maturity compost, and at the same time reduce gaseous emissions. As an added advantage, the earthworms after processing could have commercial uses.     

Effects of activated charcoal and tannin added to compost and to soil on carbon dioxide,nitrous oxide and ammonia volatilization

Given high mineralization rates of soil organic matter addition of organic fertilizers such as compost and manure is a particularly important component of soil fertility management under irrigated subtropical conditions as in Oman. However, such applications are often accompanied by high leaching and volatilization losses of N. Two experiments were therefore conducted to quantify the effects of additions of activated charcoal and tannin either to compost in the field or directly to the soil. In the compost experiment, activated charcoal and tannins were added to compost made from goat manure and plant material at a rate of either 0.5 t activated charcoal ha^?1, 0.8 t tannin extract ha^?1, or 0.6 t activated charcoal and tannin ha^?1 in a mixed application. Subsequently, emissions of CO₂, N₂O, and NH₃ volatilization were determined for 69 d of composting. The results were verified in a 20‐d soil incubation experiment in which C and N emissions from a soil amended with goat manure (equivalent to 135 kg N ha^?1) and additional amendments of either 3 t activated charcoal ha^?1, or 2 t tannin extract ha^?1, or the sum of both additives were determined. While activated charcoal failed to affect the measured parameters, both experiments showed that peaks of gaseous CO₂ and N emission were reduced and/or occurred at different times when tannin was applied to compost and soil. Application of tannins to compost reduced cumulative gaseous C emissions by 40% and of N by 36% compared with the non‐amended compost. Tannins applied directly to the soil reduced emission of N₂O by 17% and volatilization of NH₃ by 51% compared to the control. However, emissions of all gases increased in compost amended with activated charcoal, and the organic C concentration of the activated charcoal amended soil increased significantly compared to the control. Based on these results, tannins appear to be a promising amendment to reduce gaseous emissions from composts, particularly under subtropical conditions.     

Effect of Adding Flue Gas Desulphurization Gypsum on the Transformation and Fate of Nitrogen during Composting

The objective of this study was to investigate the effect of adding flue gas desulphurization gypsum (FGDG) on the transformation and fate of nitrogen during co-composting of dairy manure and pressmud of a sugar refinery. The ammonia absorption of FGDG was investigated. The changes in compost temperature, pH, electrical conductivity (EC), moisture, organic matter, the C/N ratio, Kjeldahl N, NH₄⁺-N, NO₂^?-N, NO₃^?-N were assessed. The addition of FGDG did not significantly affect compost temperature, pH, EC, moisture, and organic matter degradation. However, the addition of FGDG significantly increased the NH₄⁺-N content in the compost during the thermophilic phase, and the NH₄⁺-N maximal content in the compost with FGDG (CP+G) was 59.9% more than that in the compost without FGDG (CP–G). FGDG was thought to create the formation of (NH₄)₂SO₄ and the cation exchange between NH₄⁺ and Ca²⁺. The NO₂^?-N content in the CP+G peaked on day 15, and was not observed in the CP–G. In the final compost products, the NO₃^?-N concentration in the CP–G was more than that in the CP+G, which was 1451 (CP–G) and 1109 mg·kg^?1 (CP+G) dry material. This might be due to the NO₂^? accumulation in the CP+G, which accelerated N loss in the form of N₂O. There is a strong correlation between N₂O emission and NO₂^?-N accumulation in the composting process. Compared with the original N content in the compost mixture, the N loss in CP–G and CP+G were 15.0 and 10.8%, respectively. These results revealed that NH₄⁺-N conservation effect was improved during the thermophilic phase and the total N loss was mitigated by adding FGDG into composting materials. FGDG could be utilized as a potential amendment to conserve nitrogen during composting.     

Effect of sodium chloride on denitrification in glucose amended soil treated with ammonium and nitrate nitrogen

Laboratory incubations were conducted to study the effect of sodium chloride (NaCl) on denitrification and respiratory gases (CO₂, O₂) from soil treated with ammonium or nitrate and incubated at 20 % moisture. The same samples were assayed for denitrifying enzyme activity (DEA) after incubation at 40 % moisture with glucose and NO₃^–. Under aerobic conditions (20 % water content), a flush of activity was observed at 6 hours after start of incubation and subsided to negligible levels at 12 hours. Sodium chloride significantly depressed N₂O and CO₂ emissions and O₂ consumption. Significantly more loss of N₂O occurred from NH₄⁺‐ than NO₃^–‐treated soil at all NaCl levels and was attributed to higher microbial activity. A highly significant positive correlation was obtained between N₂O emission and respiratory gases. The respiratory quotient (CO₂ evolved/O₂) was higher for NH₄⁺‐treated soil and decreased with the amount of NaCl. At 40 % moisture, N₂O emissions were higher than at 20 % and peaked at 37 hours followed by a sharp decrease. Short‐term incubations of soil with NH₄⁺ or NO₃^– did not have an effect on denitrifying enzyme activity (DEA) while NaCl had a positive effect, particularly in previously NO₃^–‐treated soil.     

Carbon dioxide and gaseous nitrogen emissions from biochar‐amended soils under wastewater irrigated urban vegetable production of Burkina Faso and Ghana

To quantify carbon (C) and nitrogen (N) losses in soils of West African urban and peri‐urban agriculture (UPA) we measured fluxes of CO₂‐C, N₂O‐N, and NH₃‐N from irrigated fields in Ouagadougou, Burkina Faso, and Tamale, Ghana, under different fertilization and (waste‐)water regimes. Compared with the unamended control, application of fertilizers increased average cumulative CO₂‐C emissions during eight cropping cycles in Ouagadougou by 103% and during seven cropping cycles in Tamale by 42%. Calculated total emissions measured across all cropping cycles reached 14 t C ha^?1 in Ouagadougou, accounting for 73% of the C applied as organic fertilizer over a period of two years at this site, and 9 t C ha^?1 in Tamale. Compared with unamended control plots, fertilizer application increased N₂O‐N emissions in Ouagadougou during different cropping cycles, ranging from 37 to 360%, while average NH₃‐N losses increased by 670%. Fertilizer application had no significant effects on N₂O‐N losses in Tamale. While wastewater irrigation did not significantly enhance CO₂‐C emissions in Ouagadougou, average CO₂‐C emissions in Tamale were 71% (1.6 t C ha^?1) higher on wastewater plots compared with those of the control (0.9 t C ha^?1). However, no significant effects of wastewater on N₂O‐N and NH₃‐N emissions were observed at either location. Although biochar did not affect N₂O‐N and NH₃‐N losses, the addition of biochar could contribute to reducing CO₂‐C emissions from urban garden soils. When related to crop production, CO₂‐C emissions were higher on control than on fertilized plots, but this was not the case for absolute CO₂‐C emissions.     

Composting and Value-Added Utilization of Manure From a Swine Finishing Facility

Swine manure and wood shavings used as a drying bed were removed from a High-Rise? hog facility following two production cycles. The manure was composted in aerated pilot-scale vessels for four weeks or a mechanically turned windrow for ten weeks. Total dry matter losses during the pilot-scale studies were 30 and 32.5 % for continuously and intermittently aerated systems, respectively. Compost from both systems was stable with emission rates of 0.07-0.11 mgCO₂ h^?1 g_vs^?1. Moisture, O₂, CO₂ and NH₃ use/losses during the process as well as chemical properties of the initial and composted manure are presented. Incorporation of the compost at a 5% amendment rate (v/v) into a standard pine bark container medium significantly (P = 0.05) increased growth of two woody plant species. Higher amendment rates were toxic to some plants due to high initial NH₄⁺ concentrations in the medium. The compost significantly (P=0.05) increased growth and suppressed Pythium root rot of poinsettia when incorporated at 10% (v/v) into a standard sphagnum peat mix. The compost can be utilized as a value-added disease-suppressive product in the ornamentals industry.     

Emissions of CO2 and N2O from a pasture soil from Madagascar—Simulating conversion to direct‐seeding mulch‐based cropping in incubations with organic and inorganic inputs

In the highlands of Madagascar, agricultural expansion gained on grasslands and cropping systems based on direct seeding with permanent vegetation cover are emerging as a means to sustain upland crop production. The objective of this study was to examine how such agricultural practices affect greenhouse‐gas emissions from a loamy Ferralsol previously used as a pasture. We conducted an experiment under controlled laboratory conditions combining cattle manure, crop residues (rice straw), and mineral fertilizers (urea plus NPK or di‐NH₄‐phosphate) to mimic on‐field inputs and examined soil CO₂ and N₂O emissions during a 28‐d incubation at low and high water‐filled pore space (40% and 90% WFPS). Emissions of N₂O from the control soil, i.e., soil receiving no input, were extremely small (< 5 ng N₂O‐N (g soil)^–1 h^–1) even under anaerobic conditions. Soil moisture did not affect the order of magnitude of CO₂ emissions while N₂O fluxes were up to 46 times larger at high soil WFPS, indicating the potential influence of denitrification under these conditions. Both CO₂ and N₂O emissions were affected by treatments, incubation time, and their interactions. Crop‐residue application resulted in larger fluxes of CO₂ but reduced N₂O emissions probably due to N immobilization. The use of di‐NH₄‐phosphate was a better option than NPK to reduce N₂O emissions without increasing CO₂ fluxes when soil received mineral fertilizers. Further studies are needed to translate the findings to field conditions and relate greenhouse‐gas budgets to crop production.     

How do greenhouse gas emissions vary with biofertilizer type and soil temperature and moisture in a tropical grassland?

Greenhouse gases are known to play an important role in global warming. In this study, we determined the effects of selected soil and climate variables on nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) emissions from a tropical grassland fertilized with chicken slurry, swine slurry, cattle slurry, and cattle compost. Cumulative N₂O emissions did not differ between treatments and varied from 29.26 to 32.85 mg N m^-2. Similarly, cumulative CH₄ emissions were not significantly different among the treatments and ranged from 6.34 to 57.73 mg CH₄ m^-2. Slurry and compost application induced CO₂ emissions that were significantly different from those in the control treatment. The CH₄ conversion factors measured were 0.21%, 1.39%, 4.39%, and 5.07% for cattle compost, chicken slurry, swine slurry, and cattle slurry, respectively, differing from the recommendations of the Intergovernmental Panel on Climate Change (IPCC). The fraction of added N emitted as N₂O was 0.39%, which was lower than the IPCC default value of 2%. Our findings suggest that N₂O emissions could be mitigated by replacing synthetic fertilizer sources with either biofertilizer or compost. Our results indicate the following:N₂O emission was mainly controlled by soil temperature, followed by soil moisture and then soil NH₄⁺ content; CH₄ fluxes were mainly controlled by soil moisture and chamber headspace temperature; and CO₂ fluxes were mainly controlled by chamber headspace temperature and soil moisture.     

Effect of Woody Peat as an Additive on Maturity and Gaseous Emissions During Pig Manure Composting

Woody peat was used as an additive to compost with pig manure in 1.2 m³ composting reactors under aerobic conditions for a 77?days period to estimate the effect on the compost maturity and gaseous emissions (NH₃, N₂O, and CH₄). Pig manure was also composted with cornstalks (the traditional method) as a control treatment. The results showed that both cornstalks and woody peat composts reached the required maturity standard. Composting with woody peat as a bulking agent was found to reduced NH₃ emissions by 36% than the cornstalks amended treatment. Although CH₄ emission increased by adding woody peat, N₂O emission was considerably reduced, resulting in a slight decrease in total greenhouse gas emissions. More importantly, woody peat could reduce the losses of total carbon and total nitrogen, improve the compost quality as fertilizer.     

堆肥反应器中硫磺对牛粪好氧堆肥的保氮效果研究

利用堆肥反应器严格控制堆肥条件,以牛粪和蘑菇渣为原料进行好氧堆肥,在堆肥过程中添加硫磺粉,研究硫磺对堆肥温度、pH、氮素转化、硫素转化和保氮效果的影响。结果表明,堆肥中添加0.5%硫磺粉（T1）对堆肥温度没有显著影响,高温期（≥50℃）维持5.5 d; 而添加1.0%硫磺粉(T2)能快速升温,但堆肥高温期维持时间4.6 d。添加不同量的硫磺粉均能显著降低堆肥pH,与CK比较差异显著。添加硫磺粉能大幅度增加铵态氮含量,至堆肥结束时,T1和T2处理铵态氮含量分别是CK处理的15倍和24倍,差异极显著; 还增加了堆肥有效硫含量,至堆肥结束T1和T2有效硫含量分别较堆肥初始增加35.7%和77.1%。整个堆肥过程总氮（TN）含量呈增加的趋势,堆肥结束时CK、T1和T2处理的TN含量分别达15.8、16.5和16.9 g/kg,T1和T2分别比CK处理增加4.4%和7.0%。说明在牛粪好氧堆肥中添加0.5%或1.0%硫磺粉,均可起到一定的保氮作用,可大幅度提高堆肥铵态氮和有效硫的含量,改善了堆肥养分品质; 而且添加1.0%硫磺粉效果好于0.5%硫磺粉。但是添加1.0%硫磺粉缩短了堆肥高温期,降低了种子发芽指数,不利于堆肥的无害化进程。     

Nitrous Oxide and Carbon Dioxide Emissions from Vietnamese Soil Amended with Different Compost Types at High Temperature

This study aims to determine the effects of compost additions and high temperature on N₂O and CO₂ emissions from a Vietnamese agricultural soil. Soil samples amended with two compost types (commercial compost, SH and chicken compost, CC) at three rates of 1%, 2% and 4% w/w were aerobically incubated at 25°C, 30°C and 35°C for 28 days in the laboratory. N₂O and CO₂ emissions were determined on days 1, 3, 5, 7, 14, 21 and 28. Our results showed that N₂O and CO₂ emissions were significantly affected by temperature, compost additions, and their interactions. Greater N₂O and CO₂ emissions were seen in CC treatments than SH treatments. Higher application rates of CC led to greater N₂O and CO₂ emissions. In SH treatments, higher temperature lowered N₂O emissions but did not affect CO₂ emissions. N₂O and CO₂ emissions were enhanced with CC addition while they showed different responses to increasing temperature.     

Effect of temperature on the mineralization of C and N of fresh and mature compost in sandy material

Information about the mineralization rate of compost at various temperatures is a precondition to optimize mineral N fertilization and to minimize N losses in compost‐amended soils. Objectives were to quantify the influence of the temperature on the mineralization rate and leaching of dissolved organic carbon (DOC) and nitrogen (DON), NO₃^—, and NH₄⁺ from a fresh (C : N = 15.4) and a mature (C : N = 9.2) organic household waste compost. Compost samples were mixed with quartz sand to ensure aerobic conditions, incubated at 5, 10, 15, 20, and 25°C and irrigated weekly for 112 days. For the fresh compost, cumulative CO₂ evolution after 112 days ranged from 36% of the initial C content at 5°C to 54% at 25°C. The CO₂ evolution was only small in the experiments with mature compost (1 to 6% of the initial C content). The data were described satisfactorily by a combined first‐order (fresh compost) or a first‐order kinetic model (mature compost). For the fresh compost, cumulative DOC production was negatively related to the temperature, probably due to leaching of some of the partly metabolized easily degradable fractions at lower temperatures. The production ratios of DOC : CO₂‐C decreased with increasing temperature from 0.094 at 5°C to 0.038 at 25°C for the fresh and from 1.55 at 5°C to 0.26 at 25°C for the mature compost. In the experiments with fresh compost, net release of NO₃^— occurred after a time lag which depended on the temperature. Cumulative net release of NO₃^— after 112 days ranged from 1.8% of the initial N content at 5°C to 14.3% at 25°C. Approximately 10% of the initial N content of the mature compost was released as NO₃^— after 14 days at all temperatures. The DOC : DON ratios in the experiments using fresh compost ranged from 11.5 to 15.7 and no temperature dependency was observed. For the mature compost, DOC : DON ratios were slightly smaller (7.4 to 8.9). The DON : (NH₄⁺ + NO₃^—) ratio decreased with increasing temperature from 0.91 at 5°C to 0.19 at 25°C for the fresh compost and from 0.21 at 5°C to 0.12 at 25°C for the mature compost. The results of the dynamics of C and N mineralization of fresh and mature compost can be used to assess the appropriate application (timing and amount) of compost to soils.     

Combined effects of nitrogen deposition and biochar application on emissions of N2O,CO2 and NH3 from agricultural and forest soils

Abstract

Both nitrogen (N) deposition and biochar can affect the emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and ammonia (NH₃) from different soils. Here, we have established a simulated wet N deposition experiment to investigate the effects of N deposition and biochar addition on N₂O and CO₂ emissions and NH₃ volatilization from agricultural and forest soils. Repacked soil columns were subjected to six N deposition events over a 1-year period. N was applied at rates of 0 (N0), 60 (N60), and 120 (N120) kg Nh a^?1 yr^?1 without or with biochar (0 and 30 t ha^?1 yr^?1). For agricultural soil, adding N increased cumulative N₂O emissions by 29.8% and 99.1% (p < 0.05) from the N60 and N120 treatments, respectively as compared to without N treatments, and N120 emitted 53.4% more (p < 0.05) N₂O than the N60 treatment; NH₃ volatilization increased by 33.6% and 91.9% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 43.6% more (p < 0.05) NH₃ than N60; cumulative CO₂ emissions were not influenced by N addition. For forest soil, adding N significantly increased cumulative N₂O emissions by 141.2% (p < 0.05) and 323.0% (p < 0.05) from N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 75.4% more (p < 0.05) N₂O than N60; NH₃ volatilization increased by 39.0% (p < 0.05) and 56.1% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and there was no obvious difference between N120 and N60 treatments; cumulative CO₂ emissions were not influenced by N addition. Biochar amendment significantly (p < 0.05) decreased cumulative N₂O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively, and increased CO₂ emissions slightly by 7.2% and NH₃ volatilization obviously by 21.0% in the agricultural soil, while significantly decreasing CO₂ emissions by 31.5% and NH₃ volatilization by 22.5% in the forest soil. These results suggest that N deposition would strengthen N₂O and NH₃ emissions and have no effect on CO₂ emissions in both soils, and treatments receiving the higher N rate at N120 emitted obviously more N₂O and NH₃ than the lower rate at N60. Under the simulated N deposition circumstances, biochar incorporation suppressed N₂O emissions in both soils, and produced contrasting effects on CO₂ and NH₃ emissions, being enhanced in the agricultural soil while suppressed in the forest soil.     

Chemical and microbiological parameters for the characterisation of the stability and maturity of pruning waste compost

Composting of pruning waste, leaves and grass clippings was monitored by different parameters. A windrow composting pile, having the dimensions 2.5 m (height) x 30 m (length) was establish. The maturation of pruning waste compost was accompanied by a decline in NH₄ ⁺-N concentration, water soluble C (WSC) and an increase in NO₃ ^–-N content. Both organic matter (OM) content and total N (TN) losses during composting followed a first-order kinetic equation. These results were in agreement with the microbiological activity measured either by the CO₂ respiration or dehydrogenase (DH-ase) activity during the process. Statistically significant correlations were found between DH-ase activity, easily biodegradable organic C forms, NH₄ ⁺-N and NO₃ ^–-N concentrations and organic matter content and N losses. For this reason, DH-ase activity and the CO₂ evolution could be used as good indicators of pruning waste compost maturity. In contrast, humification parameters data from the organic matter fractionation did not agree with the initially expected values and did not contribute to the assessment of compost maturity. Neither the cation exchange capacity nor the germination index showed a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.     

A Newly Isolated Thermophilic Bacterium,Bacillus Licheniformis HA1 to Accelerate the Organic Matter Decomposition in High Rate Composting

Efficacy of various compost starter cultures was tested in a bench-scale composting system utilizing a ceiling process temperature of 60°C. Variables tested with time were CO₂ and NH₃ evolution, conversion of carbon and the succession of microorganisms in the compost. When an initial compost pH of 7.0 was used, a laboratory produced starter culture (Culture A) was much less effective than a commercial culture (Culture B). Low activity in the experiment with Culture A was due to a low pH(<5.5) that developed within 30 h after inoculation. Inoculation of Culture A with a thermophilic strain (HA1) of Bacillus licheniformis isolated from Culture B prevented the decrease in pH and significantly increased the rate of decomposition. It also enhanced populations of other thermophilic bacterial groups during the process.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.     

Nitrous oxide, methane and ammonia emissions following slurry spreading on grassland

In Sweden, 90% of ammonia (NH₃) emissions to the atmosphere originate from agriculture, predominantly from animal manure handling. It is well known that incorporation of manure into soil can reduce NH₃ emissions after spreading. However, there is a risk of increased nitrous oxide (N₂O) and methane (CH₄) emissions caused by bacterial activity and limited oxygen availability under these conditions. A full‐scale injector was developed and evaluated in a field experiment on grassland. Cattle slurry was either injected in closed slots 5 cm below ground or band spread on the soil surface above the crop canopy at a rate of 25 t ha^?1. In a control treatment, no slurry was applied. During a 5‐day period after application, NH₃ emissions were measured using an equilibrium concentration method. Gas samples for estimating CH₄ and N₂O emissions were also collected during 7 weeks following slurry application. Injection in closed slots resulted in no detectable NH₃ emissions. After band spreading, however, NH₃ emissions corresponded to nearly 40% of the total ammoniacal nitrogen in the applied slurry. The injection of slurry gave rise to a broad peak of N₂O emissions during the first 3 weeks after application. In total, for the measuring period, N₂O emissions corresponded to 0.75 kg N ha^?1. Band spreading resulted in only a very small N₂O release of about 0.2 kg N ha^?1 during the same period. Except for the first sampling occasion, the soil was predominantly a sink for CH₄ in all the treatments. The use of the injector without slurry application reduced grass yield during unfavourable growing conditions. In conclusion, shallow injection in closed slots seems to be a promising technique to reduce negative environmental impacts from NH₃ emissions with a limited release of N₂O and CH₄.     

C and N dynamics of a range of biogas slurries as a function of application rate and soil texture: a laboratory experiment

Digestates vary in composition and studies regarding their impact on C and N dynamics in soils are scarce. The objective was to analyse the C and N dynamics of digestates originating from various substrates applied to a sandy Cambisol and a silty Anthrosol. In three laboratory experiments (4–6 weeks), the effects of digestate properties, N rate and water content were tested. Averaged over both soils, 21% of the C supplied was emitted as CO₂. Potential NH₃ emissions during the first week ranged between 6% and 12% of NH₄⁺ present in the digestates. The emission factors in the sandy Cambisol were on average 1.2 and 2 times higher for CO₂ and potential NH₃, respectively, compared to the silty Anthrosol. Similarly, net nitrogen mineralization in the sandy Cambisol was approximately twice the N mineralized in the silty Anthrosol. Net nitrification was not influenced by soil texture or different digestates, but increased with increasing application rates and had highest values at 75% of water holding capacity. Our results indicate that the type of substrate input for anaerobic digestion influences the properties of the digestate and therefore the dynamics of C and N. However, soil texture can affect these dynamics markedly.     

Effects of transient anaerobic conditions in the presence of acetylene on subsequent aerobic respiration and N2O emission by soil aggregates

Our objective was to assess the effect of anaerobic conditioning in the presence of acetylene on subsequent aerobic respiration and N₂O emission at the scale of soil aggregates. Nitrous oxide production was measured in intact soil aggregates Δ (compacted aggregates without visible porosity) and Γ (aggregates with visible porosity) incubated under oxic conditions, with or without anaerobic conditioning for 6 d. N₂O emissions were much higher in aggregates that had been submitted to anaerobic conditioning than in aggregates that did not experience this conditioning, although very little NO₃⁻ remained in soil after the anaerobic period. ¹⁵N isotope tracing technique was used to check whether N₂O came from nitrification or denitrification. The results showed that denitrification was the major process responsible for N₂O emissions. The aerobic CO₂ production rate was also measured in intact soil aggregates. It was greater in aggregates submitted to anaerobic conditioning than in those that were not, suggesting that the anaerobic conditioning lead to an accumulation of small compounds including fatty acids that are readily available for microbial decomposition in aerobic conditions. This process increases the aerobic CO₂ production and favours the N₂O emissions through denitrification.     

Short‐term N2O,CO2, NH3 fluxes,and N/C transfers in a Danish grass‐clover pasture after simulated urine deposition in autumn

Urine patches are significant hot‐spots of C and N transformations. To investigate the effects of urine composition on C and N turnover and gaseous emissions from a Danish pasture soil, a field plot study was carried out in September 2001. Cattle urine was amended with two levels of ¹³C‐ and ¹⁵N‐labeled urea, corresponding to 5.58 and 9.54 g urea‐N l^–1, to reflect two levels of protein intake. Urine was then added to a sandy‐loam pasture soil equivalent to a rate of 23.3 or 39.8 g urea‐N m^–2. Pools and isotopic labeling of nitrous oxide (N₂O) and CO₂ emissions, extractable urea, ammonium (NH₄⁺), and nitrate (NO₃^–), and plant uptake were monitored during a 14 d period, while ammonia (NH₃) losses were estimated in separate plots amended with unlabeled urine. Ammonia volatilization was estimated to account for 14% and 12% of the urea‐N applied in the low (UL) and high (UH) urea treatment, respectively. The recovery of urea‐derived N as NH₄⁺ increased during the first several days, but isotopic dilution was significant, possibly as a result of stress‐induced microbial metabolism. After a 2 d lag phase, nitrification proceeded at similar rates in UL and UH despite a significant difference in NH₄⁺ availability. Nitrous oxide fluxes were low, but generally increased during the 14 d period, as did the proportion derived from urea‐N. On day 14, the contribution from urea was 23% (UL) and 13% (UH treatment), respectively. Cumulative total losses of N₂O during the 14 d period corresponded to 0.021% (UL) and 0.015% (UH) of applied urea‐N. Nitrification was probably the source of N₂O. Emission of urea‐derived C as CO₂ was only detectable within the first 24 h. Urea‐derived C and N in above‐ground plant material was only significant at the first sampling, indicating that uptake of urine‐C and N via the leaves was small. Urine composition did not influence the potential for N₂O emissions from urine patches under the experimental conditions, but the importance of site conditions and season should be investigated further.