Source Apportionment of Atmospheric Ammonia at 16 Sites in China Using a Bayesian Isotope Mixing Model Based on δ15N-NHx Signatures.

Reducing atmospheric ammonia (NH3) emissions is critical to mitigating poor air quality. However, the contributions of major agricultural and non-agricultural source emissions to NH3 at receptor sites remain uncertain in many regions, hindering the assessment and implementation of effective NH3 reduction strategies. This study conducted simultaneous measurements of the monthly concentrations and stable nitrogen isotopes of NHx (gaseous NH3 plus particulate NH4+) at 16 sites across China. Ambient NHx concentrations averaged 21.7 ± 19.6 µg m-3 at rural sites, slightly higher than those at urban (19.2 ± 6.0 µg m-3) and three times of those at background (7.0 ± 6.9 µg m-3) sites. Based on revised δ15N values of the initial NH3, source apportionment results indicated that non-agricultural sources (traffic and waste) and agricultural sources (fertilizer and livestock) contributed 54 and 46% to NH3 at urban sites, 51 and 49% at rural sites, and 61 and 39% at background sites, respectively. Non-agricultural sources contributed more to NH3 at rural and background sites in cold than warm seasons, arising from traffic and waste, but were similar across seasons at urban sites. We concluded that non-agricultural sources need to be addressed when reducing ambient NH3 across China, even in rural regions.

Effects of hotter, drier conditions on gaseous losses from nitrogen fertilisers.

Global warming is expected to cause hotter, drier summers and more extreme weather events including heat waves and droughts. A little understood aspect of this is its effects on the efficacy of fertilisers and related nutrient losses into the environment. We explored the effects of high soil temperature (>25 °C) and low soil moisture (<40% water filled pore space; WFPS) on emissions of ammonia (NH3) and nitrous oxide (N2O) following application of urea to soil and the efficacy of urease inhibitors (UI) in slowing N losses. We incubated soil columns at three temperatures (15, 25, 35 °C) and three soil moisture contents (20, 40, 60% WFPS) with urea applied on the soil surface with and without UIs, and measured NH3 and N2O emissions using chambers placed over the columns. Four fertiliser treatments were applied in triplicate in a randomised complete block design: (1) urea; (2) urea with a single UI (N-(n-butyl) thiophosphoric triamide (NBPT); (3) urea with two UI (NBPT and N-(n-propyl) thiophosphoric triamide; NPPT); and (4) a zero N control. Inclusion of UI with urea, relative to urea alone, delayed and reduced peak NH3 emissions. However, the efficacy of UI was reduced with increasing temperature and decreasing soil moisture. Cumulative NH3 emission did not differ between the two UI treatments for a given set of conditions and was reduced by 22-87% compared with urea alone. Maximum cumulative NH3 emission occurred at 35 °C and 20% WFPS, accounting for 31% of the applied N for the urea treatment and 25%, on average for the UI treatments. Urease inhibitors did not influence N2O emissions; however, there were interactive impacts of temperature and moisture, with higher cumulative emissions at 40% WFPS and 15 and 25 °C accounting for 1.85-2.62% of the applied N, whereas at 35 °C there was greater N2O emission at 60% WFPS. Our results suggest that inclusion of UI with urea effectively reduces NH3 losses at temperatures reaching 35 °C, although overall effectiveness decreases with increasing temperature, particularly under low soil moisture conditions.

Revisiting sampling duration to estimate N2O emission factors for manure application and cattle excreta deposition for the UK and Ireland.

According to the available guidelines, good practices for calculating nitrous oxide (N2O) emission factors (EFs) for livestock excreta and manure application include that sampling duration should be of at least one year after the nitrogen (N) application or deposition. However, the available experimental data suggest that in many cases most emissions are concentrated in the first months following N application. Therefore resources could be better deployed by measuring more intensively during a shorter period. This study aimed to assess the contribution of the N2O flux in the period directly after N application to the annual net emission. We used a database of 100 year-long plot experiments from different excreted-N sources (dung, urine, farmyard manure and slurry) used to derive EFs for the UK and Ireland. We explored different shorter potential measurement periods that could be used as proxies for cumulative annual emissions. The analysis showed that the majority of emissions occur in the first months after application, especially in experiments that i) had urine as the N source, ii) had spring N application, iii) were conducted on fine-textured soils, or iv) showed high annual emissions magnitude. Experiments that showed a smaller percentage of emissions in the first months also had a low magnitude of annual net emissions (below 370 gN2O-N ha-1 year-1), so the impact of measuring during a shorter period would not greatly influence the calculated EF. Accurate EF estimations were obtained by measuring for at least 60 days for urine (underestimation: 7.1%), 120 days for dung and slurry (4.7 and 5.1%) and 180 days for FYM (1.4%). At least in temperate climates, these results are promising in terms of being able to estimate annual N2O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs.

Equations to predict nitrogen outputs in manure, urine and faeces from beef cattle fed diets with contrasting crude protein concentration.

Accurately predicting nitrogen (N) outputs in manure, urine and faeces from beef cattle is crucial for the realistic assessment of the environmental footprint of beef production and the development of sustainable N mitigation strategies. This study aimed to develop and validate equations for N outputs in manure, urine and faeces for animals under diets with contrasting crude protein (CP) concentrations. Measurements from individual animals (n = 570), including bodyweight, feed intake and chemical composition, and N outputs were (i) analysed as a merged database and also (ii) split into three sub-sets, according to diet CP concentration (low CP, 84-143 g/kg dry matter, n = 190; medium CP, 144-162 g/kg dry matter, n = 190; high CP, 163-217 g/kg dry matter, n = 190). Prediction equations were developed and validated using residual maximum likelihood analysis and mean prediction error (MPE), respectively. In low CP diets the lowest MPE for N outputs in manure, urine and faeces was 0.244, 0.594 and 0.263, respectively; diet CP-specific equations improved accuracy in certain occasions, by 4.9% and 18.3% for manure N output and faeces N output respectively, while a reduction by 5.7% in the prediction accuracy for urinary N output was noticed. In medium CP diets the lowest MPE for N outputs in manure, urine and faeces was 0.227, 0.391 and 0.394, respectively; diet CP-specific equations improved accuracy by 13.2%, 41.2% and 16.8% respectively. In high CP diets the lowest MPE for N outputs in manure, urine and faeces was 0.120, 0.154 and 0.144, respectively; diet CP-specific equations improved accuracy in certain occasions by 5.8%, 9.1% and 6.3% respectively. This study demonstrated that for improved prediction accuracy of N outputs in manure, urine and faeces from beef cattle, the use of dietary CP concentration is essential while dietary starch, fat, and metabolisable energy concentrations can be used to further improve accuracy. In beef cattle fed low CP concentration diets, using diet CP-specific equations improves prediction accuracy when feed intake or dietary CP concentration are not known. However, in beef cattle fed medium or high CP concentration diets, using equations that have been developed from animals fed similar CP concentration diets, substantially improves the prediction accuracy of N outputs in manure, urine and faeces in most cases.

Measured ammonia emissions from tropical and subtropical pastures: A comparison with 2006 IPCC, 2019 Refinement to the 2006 IPCC, and EMEP/EEA (European Monitoring and Evaluation Programme and European Environmental Agency) inventory estimates.

Agriculture is the largest source of ammonia (NH3) emissions. As NH3 is an indirect greenhouse gas, NH3 measurements are crucial to improving greenhouse gas emission inventory estimates. Moreover, NH3 emissions have wider implications for environmental and human health. Only a few studies have measured NH3 emissions from pastures in the tropics and subtropics and none has compared emissions to inventory estimates. The objectives of this study were to (1) measure NH3 emissions from dairy pastures in tropical and subtropical regions; (2) calculate NH3 emissions factors (EF) for each campaign; and (3) compare measured EF with those based on the 2006 Intergovernmental Panel on Climate Change (IPCC) Tier 1, 2019 Refinement to the 2006 IPCC Tier 1, and the European Monitoring and Evaluation Programme/European Environmental Agency (EMPE/EEA) Tier 2 inventory estimates. Pasture NH3 emissions were measured on 3 dairy farms in Costa Rica. On each dairy, NH3 emissions were measured twice during the wet season and once during the dry season using a micrometeorological integrated horizontal-flux mass-balance method. Emissions were measured from excreta (dung and urine) deposited by grazing cattle and the subsequent application of organic (slurry) or synthetic fertilizer (ammonium nitrate or urea). Measured EF for all campaigns [from grazing cattle excreta and any subsequent slurry or fertilizer application; 4.9 ± 0.9% of applied nitrogen (mean ± SE)] were similar to those of the EMEP/EEA Tier 2 approach (6.1 ± 0.9%; mean ± SE) and 4 times lower than 2006 IPCC and 2019 Refinement to 2006 IPCC Tier 1 default estimates (17.7 ± 1.4 and 18.2 ± 0.9%, respectively; mean ± SE). Measured EF for excreta deposited on pasture and excreta both deposited on pasture and slurry application [3.9 ± 2.1 and 4.2 ± 2.1% (mean ± 95% CI), respectively] were 5 times lower than default EF assumed by 2006 IPCC and 2019 Refinement to 2006 IPCC methodology (both 20 and 21%, respectively), whereas EMEP/EAA estimates were similar [6.0 and 4.6 ± 0.3% (mean ± 95% CI), respectively]. This suggests an overestimation of EF from excreta deposited on pasture and slurry applications in tropical and subtropical regions by IPCC methodologies. Furthermore, rainfall, which is not included as a parameter in the current EMEP/EEA Tier 2 methodology, appeared to reduce NH3 emissions, suggesting that accounting for this in the inventory methodologies could improve inventory estimates.

Fate and transfer of heavy metals following repeated biogas slurry application in a rice-wheat crop rotation.

The application of biogas slurry, from anaerobic digestion of livestock excreta, to cropland has proven to be an effective mechanism for recycling nutrients within farms. However, the potential pollution of heavy metals from repeated biogas slurry fertilization has not received much attention. Here we present the results of a field experiment under rice-wheat rotation demonstrating the accumulation, speciation distribution and plant uptake of heavy metals (Cu, Zn, Pb and Cd) in soil following biogas slurry application. The treatments were: zero biogas slurry application (BS0), and biogas slurry application for three (BS3) and five (BS5) years, at a rate of 450 m3 ha-1 y-1. Our findings show that biogas slurry fertilization resulted in accumulation of Cu and Zn in the soil. The concentrations of soil Cu and Zn under BS5 were, respectively, 38 and 29% greater in the wheat season and 35 and 35% greater in the rice season relative to BS0 (p < 0.05). The bioavailability of soil Cu and Zn increased following biogas slurry application. Plant uptake of Cu and Zn to all parts of wheat and rice plants (excluding Cu in wheat straw) increased with the years of biogas slurry application (p < 0.05), and the concentration of Cd in wheat grain was significantly greater in BS5 relative to BS0 (p < 0.05). After five years of biogas slurry fertilization, concentrations of Cu, Zn, Pb and Cd in wheat grains were 3.28, 25.19, 0.11 and 0.053 mg kg-1 and 4.24, 33.78, 0.12 and 0.035 mg kg-1 for rice grains, respectively, all within the safety limits. Our results demonstrate that repeated biogas slurry fertilization for five years has a relatively low pollution risk of heavy metals. However, long-term field monitoring and co-application with metal-immobilizing materials are required to ensure the safety of its application to cropland.

Acidification of manure reduces gaseous emissions and nutrient losses from subsequent composting process.

Manure acidification is recommended to minimize ammonia (NH3) emission at storage. However, the potential for acidification to mitigate NH3 emission from storage and the impact of manure acidification (pH range 5-8) on composting have been poorly studied. The effects of manure acidification at storage on the subsequent composting process, nutrient balance, gaseous emissions and product quality were assessed through an analysis of literature data and an experiment under controlled conditions. Results of the data mining showed that mineral acids, acidic salts and organic acids significantly reduced NH3 emission, however, a weaker effect was observed for organic acids. A subsequent composting experiment showed that using manure acidified to pH5 or pH6 as feedstock delayed organic matter degradation for 7-10 days, although pH6 had no negative effect on compost maturity. Acidification significantly decreased NH3 emission from both storage and composting, however, excessive acidification (pH5) enhanced N2O emissions (18.6%) during composting. When manure was acidified to pH6, N2O (17.6%) and CH4 (20%) emissions, and total GHG emissions expressed as global warming potential (GWP) (9.6%) were reduced during composting. Acidification of manure before composting conserved more N as NH4+ and NOx- in compost product. Compared to the control, the labile, plant-available phosphorus (P) content in the compost product, predominately as water-soluble inorganic P, increased with manure acidification to pH5 and pH6. Acidification of manure to pH6 before composting decreases nutrient losses and gaseous emissions without decreasing the quality of the compost product. The techno-economic advantages of acidification should be further ascertained.

Fate and transport of urea-N in a rain-fed ridge-furrow crop system with plastic mulch.

A better understanding of the fate and transport of fertilizer nitrogen (N) is critical to maximize crop yields and minimize negative environmental impacts. Plastic film mulching is widely used in drylands to increase soil water use efficiency and crop yields, but the effects on fertilizer N use efficiency need to be evaluated. A field experiment with 15N-urea (260 kg N ha-1) was conducted to determine the fate and transport of fertilizer N in a ridge-furrow system with plastic film mulched ridge (Plastic), compared with a flat system without mulching (Open). In the Plastic, the 15N-urea was applied to the ridge only (Plastic-Ridge), or to the furrow only (Plastic-Furrow). Maize grain yield and net economic benefit for Plastic were significantly higher (by 9.7 and 8.5%, respectively) than those for Open. Total plant 15N uptake was 72.5% greater in Plastic compared with Open, and 15N was allocated mostly to the grain. Losses of the applied urea-N were 54.5% lower in Plastic and much more residual 15N was recovered in 0-120 cm soil compared with Open (42.7 and 26.8% of applied 15N, respectively). Lateral N movements from furrow to ridge and from ridge to furrow were observed and attributed to lateral movement of soil water due to microtopography of ridges and furrows and uneven soil water and heat conditions under mulching and plant water uptake. The ridges were the main N fertilizer source for plant uptake (96.5 and 3.5% of total N uptake in Plastic from ridge and furrow, respectively) and the furrow was the main source of N losses (78.6 and 21.4% of total N losses in Plastic from furrow and ridge, respectively). Gas emissions, especially ammonia volatilization was probably the main N loss in furrow. Thus, appropriately localized N application - into the ridges, and management strategies should be designed for Plastic to maximize N use efficiency by crops, decrease N gas losses and maintain sustainable agricultural systems in drylands.

Dry matter losses and quality changes during short rotation coppice willow storage in chip or rod form.

This study compares dry matter losses and quality changes during the storage of SRC willow as chips and as rods. A wood chip stack consisting of approximately 74 tonnes of fresh biomass, or 31 tonnes dry matter (DM) was built after harvesting in the spring. Three weeks later, four smaller stacks of rods with an average weight of 0.8 tonnes, or 0.4 tonnes DM were built. During the course of the experiment temperature recorders placed in the stacks found that the wood chip pile reached 60 °C within 10 days of construction, but the piles of rods remained mostly at ambient temperatures. Dry matter losses were calculated by using pre-weighed independent samples within the stacks and by weighing the whole stack before and after storage. After 6 months the wood chip stack showed a DM loss of between 19.8 and 22.6%, and mean losses of 23.1% were measured from the 17 independent samples. In comparison, the rod stacks showed an average stack DM loss of between 0 and 9%, and between 1.4% and 10.6% loss from the independent samples. Analysis of the stored material suggests that storing willow in small piles of rods produces a higher quality fuel in terms of lower moisture and ash content; however, it has a higher fine content compared to storage in chip form. Therefore, according to the two storage methods tested here, there may be a compromise between maximising the net dry matter yield from SRC willow and the final fine content of the fuel.

Effects of the ridge mulched system on soil water and inorganic nitrogen distribution in the Loess Plateau of China.

The semi-arid region of the Loess Plateau is typical of rain-fed agricultural production in Northwestern China. In this area, the ridge mulched system (RM) is a widely-used measure to increase crop yield. The purpose of this study was to investigate the effect of RM on soil water and inorganic nitrogen (N) distribution, and grain yield of maize (Zea mays L.). The study was conducted over three consecutive years and consisted of four treatments (each replicated three times): i) RM with N application rate of 260 kg N ha-1 (RM-N260); ii) RM with 180 kg N ha-1 (RM-N180); iii) a traditional flat cultivation system without mulching (F) with 260 kg N ha-1 (F-N260); iv) F with 180 kg N ha-1 (F-N180). Mean soil water content during the maize growing season was increased by RM in 2013 only. However, RM increased the soil water storage significantly at the 3-leaf (V3) and 6-leaf stage (V6), and decreased evapotranspiration (ET) during pre-silking stage in all years. Compared to F, RM significantly improved maize grain yield by 79-123% in 2013, 23-25% in 2014, and 11-12% in 2015. Following three years of maize cultivation, soil inorganic N content increased substantially (two- to three-fold) in the RM system and 60% of the total inorganic N was accumulated in the top soil layers (0-60 cm) under the mulched ridge. Relative changes were much smaller in F, and most of inorganic N was stored in 0-20 cm and 100-160 cm soil layers. Generally, RM resulted in higher soil water storage during the pre-silking stage, which was the main reason for the improved maize grain yield. The nitrate leaching risk was reduced in RM-N180 compared with F, but nitrate leaching from the furrows between ridges was observed in RM-N260. However, the large increase in soil inorganic N content in RM-N180 after three years' cultivation indicates an oversupply of N and a potential risk of N losses to the environment over the longer term. Our study indicates, therefore, that RM is a suitable system for maize cropping in the semi-arid region of the Loess Plateau, with benefits in water and N use efficiency, but recommendations for appropriate N application rates are required to ensure long term agricultural sustainability, accounting for grain yields and environmental impacts. The mechanisms for inorganic N accumulation under the RM system are not fully understood and warrant further investigation.

Impacts of plastic film mulching on crop yields, soil water, nitrate, and organic carbon in Northwestern China: A meta-analysis.

In order to increase crop yield in semi-arid and arid areas, plastic film mulching (PFM) is widely used in Northwestern China. To date, many studies have addressed the effects of PFM on soil physical and biochemical properties in rain-fed agriculture in Northwestern China, but the findings of different studies are often contradictory. Therefore, a comprehensive review of the impacts of PFM on soil water content, soil nutrients and food production is needed. We compiled the results of 1278 observations to evaluate the overall effects of PFM on soil water content, the distribution of nitrate and soil organic carbon, and crop yield in rain-fed agriculture in Northwestern China. Our results showed that PFM increased soil moisture and nitrate concentration in topsoils (0-20 cm) by 12.9% and 28.2%, respectively, but slightly decreased (1.8%) soil organic carbon (SOC) content in the 0-10 cm soil layer. PFM significantly increased grain yields by 43.1%, with greatest effect in spring maize (79.4%). When related to cumulative precipitation during the crop growing season, yield increase from PFM was greatest (72.8%) at 200-300 mm, which was attributed to the large increase for spring maize and potato, implying that crop zoning would be beneficial for PFM in this region. When related to N application rate, crop yields benefited most from PFM (80.2%) at 200-300 kg/ha. A cost-benefit analysis indicated that PFM increased economic return by an average of 29.5%, with the best improvement for spring maize (71.1%) and no increase for spring wheat. In conclusion, PFM can significantly increase crop yield and economic return (especially for spring maize) in rain-fed agriculture areas of Northwestern China. Crop zoning is recommended for PFM to achieve the largest economic benefit. However, full account needs to be taken of the environmental impacts relating to N loss, SOC depletion and film pollution to evaluate the sustainability of PFM systems and further research is required to quantify and mitigate these impacts.

Influence of ruminal methane on digesta retention and digestive physiology in non-lactating dairy cattle.

Enteric methane (CH4) production is a side-effect of herbivore digestion, but it is unknown whether CH4 itself influences digestive physiology. We investigated the effect of adding CH4 to, or reducing it in, the reticulorumen (RR) in a 4×4 Latin square experiment with rumen-fistulated, non-lactating cows, with four treatments: (i) control, (ii) insufflation of CH4 (iCH4), (iii) N via rumen fistula, (iv) reduction of CH4 via administration of bromochloromethane (BCM). DM intake (DMI), apparent total tract digestibility, digesta mean retention times (MRT), rumen motility and chewing activity, spot breath CH4 emission (CH4exhal, litre/kg DMI) as well as CH4 dissolved in rumen fluid (CH4RRf, µg/ml) were measured. Data were analysed using mixed models, including treatment (or, alternatively, CH4exhal or CH4RRf) and DMI relative to body mass0·85 (rDMI) as covariates. rDMI was the lowest on the BCM treatment. CH4exhal was highest for iCH4 and lowest for BCM treatments, whereas only BCM affected (reduced) CH4RRf. After adjusting for rDMI, CH4RRf had a negative association with MRT in the gastrointestinal tract but not in the RR, and negative associations with fibre digestibility and measures of rumination activity. Adjusting for rDMI, CH4exhal had additionally a negative association with particle MRT in the RR and a positive association with rumen motility. Thus, higher rumen levels of CH4 (CH4exhal or CH4RRf) were associated with shorter MRT and increased motility. These findings are tentatively interpreted as a feedback mechanism in the ruminant digestive tract that aims at mitigating CH4 losses by shortening MRT at higher CH4.

Greenhouse Gas and Ammonia Emissions from Slurry Storage: Impacts of Temperature and Potential Mitigation through Covering (Pig Slurry) or Acidification (Cattle Slurry).

Storage of livestock slurries is a significant source of methane (CH) and ammonia (NH) emissions to the atmosphere, for which accurate quantification and potential mitigation methods are required. Methane and NH emissions were measured from pilot-scale cattle slurry (CS) and pig slurry (PS) stores under cool, temperate, and warm conditions (approximately 8, 11, and 17°C, respectively) and including two potential mitigation practices: (i) a clay granule floating cover (PS) and (ii) slurry acidification (CS). Cumulative emissions of both gases were influenced by mean temperature over the storage period. Methane emissions from the control treatments over the 2-mo storage periods for the cool, temperate, and warm periods were 0.3, 0.1, and 34.3 g CH kg slurry volatile solids for CS and 4.4, 20.1, and 27.7 g CH kg slurry volatile solids for PS. Respective NH emissions for each period were 4, 7, and 12% of initial slurry N content for CS and 12, 18, and 28% of initial slurry N content for PS. Covering PS with clay granules reduced NH emissions by 77% across the three storage periods but had no impact on CH emissions. Acidification of CS reduced CH and NH emissions by 61 and 75%, respectively, across the three storage periods. Nitrous oxide emissions were also monitored but were insignificant. The development of approaches that take into account the influence of storage timing (temperature) and duration on emission estimates for national emission inventory purposes is recommended.

Isotope fractionation factors controlling isotopocule signatures of soil-emitted N2O produced by denitrification processes of various rates.

RATIONALE: This study aimed (i) to determine the isotopic fractionation factors associated with N2O production and reduction during soil denitrification and (ii) to help specify the factors controlling the magnitude of the isotope effects. For the first time the isotope effects of denitrification were determined in an experiment under oxic atmosphere and using a novel approach where N2O production and reduction occurred simultaneously. METHODS: Soil incubations were performed under a He/O2 atmosphere and the denitrification product ratio [N2O/(N2 + N2O)] was determined by direct measurement of N2 and N2O fluxes. N2O isotopocules were analyzed by mass spectrometry to determine δ(18)O, δ(15)N and (15)N site preference within the linear N2O molecule (SP). An isotopic model was applied for the simultaneous determination of net isotope effects (η) of both N2O production and reduction, taking into account emissions from two distinct soil pools. RESULTS: A clear relationship was observed between (15)N and (18)O isotope effects during N2O production and denitrification rates. For N2O reduction, diverse isotope effects were observed for the two distinct soil pools characterized by different product ratios. For moderate product ratios (from 0.1 to 1.0) the range of isotope effects given by previous studies was confirmed and refined, whereas for very low product ratios (below 0.1) the net isotope effects were much smaller. CONCLUSIONS: The fractionation factors associated with denitrification, determined under oxic incubation, are similar to the factors previously determined under anoxic conditions, hence potentially applicable for field studies. However, it was shown that the η(18)O/η(15)N ratios, previously accepted as typical for N2O reduction processes (i.e., higher than 2), are not valid for all conditions.

The effect of nitrogen input on N2O emission depends on precipitation in a temperate desert steppe.

Nitrous oxide (N2O) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect N2O emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on N2O emission. The study result showed that N2O emission in this desert steppe was relatively small and did not show significant seasonal change. The annual N2O emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17th 2019) on N2O emission was greatly amplified by nearly 17-46 times by an extreme precipitation event on June 24th 2019. In contrast, this greatly promoting effect of high N input on N2O emission was not observed on September 26th 2019 by a similar extreme precipitation event. Further analysis showed that soil NH4+-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting N2O emission. Soil moisture played an important indirect role in regulating N2O emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on N2O emission was greatly increased by high N input. Furthermore, in this desert steppe, annual N2O flux is co-managed through soil nitrification substrate concentration (NH4+-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future N2O emissions from desert steppes.

Quantification of N and C cycling during aerobic composting, including automated direct measurement of N2, N2O, NO, NH3, CO2 and CH4 emissions.

Closing the carbon (C) and nitrogen (N) balance has yet to be achieved in aerobic bioprocess due to current methodological drawbacks in the frequency of sampling and detection and the challenge in direct measurement of instantaneous N2 emission. To address this issue, a novel system was developed enabling simultaneous and online determination of gaseous C and N species (N2, N2O, NO, NH3, CO2 and CH4) from aerobic composting at a high frequency of 120 times·d-1. A helium­oxygen gas mixture was used to replace the air in the system to enable direct measurement of N2 emission, and three different gas exchange methods were assessed in their ability to minimize atmospheric background N2: 1) the N2-free gas purging method; 2) one cycle of the evacuation-refilling procedure; 3) one cycle of evacuating and refilling followed by N2-free gas purging. Method 3 was demonstrated as an optimum N2-removal method, and background N2 concentrations decreased to ~66 µmol·mol-1 within 11.6 h. During the N2-free gas purging period, low temperature incubation at 15 °C reduced CO2, CH4, NO, N2O and NH3 losses by 80.5 %, 41-fold, 10-fold, 11,403-fold and 61.4 %, respectively, compared with incubation at 30 °C. Therefore, a fast and low-perturbation N2 removal method was developed, namely the evacuating/refilling-low temperature purging method. Notably, all C and N gases exhibited large within-day variations during the peak emission period, which can be addressed by high-frequency measurement. Based on the developed method, up to 97.8 % of gaseous C and 95.6 % of gaseous N losses were quantified over a 43-day compost incubation, with N2 emission accounting (on average) for 5.8 % of the initial total N. This system for high frequency measurement of multiple gases (including N2) provides a novel tool for obtaining a deeper understanding of C and N turnover and more accurate estimation of reactive N and greenhouse gas emissions during composting.

DATAMAN: A global database of methane, nitrous oxide, and ammonia emission factors for livestock housing and outdoor storage of manure.

Livestock manure management systems can be significant sources of nitrous oxide (N2 O), methane (CH4 ), and ammonia (NH3 ) emissions. Many studies have been conducted to improve our understanding of the emission processes and to identify influential variables in order to develop mitigation techniques adapted to each manure management step (animal housing, outdoor storage, and manure spreading to land). The international project DATAMAN (http://www.dataman.co.nz) aims to develop a global database on greenhouse gases (N2 O, CH4 ) and NH3 emissions from the manure management chain to refine emission factors (EFs) for national greenhouse gas and NH3 inventories. This paper describes the housing and outdoor storage components of this database. Relevant information for different animal categories, manure types, livestock buildings, outdoor storage, and climatic conditions was collated from published peer reviewed research, conference papers, and existing databases published between 1995 and 2021. In the housing database, 2024 EFs were collated (63% for NH3 , 19.5% for CH4 , and 17.5% for N2 O). The storage database contains 654 NH3 EFs from 16 countries, 243 CH4 EFs from 13 countries, and 421 N2 O EFs from 17 countries. Across all gases, dairy cattle and swine production in temperate climate zones are the most represented animal and climate categories. As for the housing database, the number of EFs for the tropical climate zone is under-represented. The DATAMAN database can be used for the refinement of national inventories and better assessment of the cost-effectiveness of a range of mitigation strategies.

The effects of electric field assisted composting on ammonia and nitrous oxide emissions varied with different electrolytes.

Enhancing electron transfer through directly elevating electric potential has been verified to reduce gaseous emissions from composting. Reducing electric resistance of composting biomass might be a choice to further strengthening electron transfer. Here, the effects of chemical electrolytes addition on gaseous Nitrogen emission in electric field assistant composting were investigated. Results suggest that adding acidic electrolyte (ferric chloride) significantly reduced ammonia (NH3) emission by 72.1% but increased nitrous oxide (N2O) emission (by 24-fold) (P < 0.05), because of a dual effect on nitrifier activity: i) an elevated abundance and proportion of ammonia oxidizing bacteria Nitrosomonadaceae, and ii) delayed growth of nitrite oxidizing bacteria. Neutral and alkaline electrolytes had no negative or positive effect on N2O or NH3 emission. Hence, there is a potential trade-off between NH3 and N2O mitigation if using ferric chloride as acidic electrolyte, and electrolyte addition should aim to enhance electron production promote N2O mitigation.