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Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N 2 O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N 2 O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N 2 O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N 2 O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N 2 O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N 2 O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N 2 O emissions., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Ammonia (NH 3 ) and nitrous oxide (N 2 O) emissions from livestock manure management have a significant impact on air quality and climate change. There is an increasing urgency to improve our understanding of drivers influencing these emissions. We analysed the DATAMAN ("DATAbase for MANaging greenhouse gas and ammonia emissions factors") database to identify key factors influencing (i) NH 3 emission factors (EFs) for cattle and swine manure applied to land and (ii) N 2 O EFs for cattle and swine manure applied to land, and (iii) cattle urine, dung and sheep urine deposited during grazing. Slurry dry matter (DM) content, total ammoniacal nitrogen (TAN) concentration and method of application were significant drivers of NH 3 EFs from cattle and swine slurry. Mixed effect models explained 14-59 % of the variance in NH 3 EFs. Apart from the method of application, the significant influence of manure DM, manure TAN concentration or pH on NH 3 EFs suggests mitigation strategies should focus on these. Identifying key factors influencing N 2 O EFs from manures and livestock grazing was more challenging, likely because of the complexities associated with microbial processes and soil physical properties impacting N 2 O production and emissions. Generally, significant factors were soil-related e.g. soil water content, pH, clay content, suggesting mitigations may need to consider the conditions of the receiving environment for manure spreading and grazing deposition. Total variability explained by terms in mixed effect model was on average 66 %, with the random effect 'experiment identification number' explaining, on average, 41 % of the total variability in the models. We suspect this term captured the effect of non-measured manure, soil and climate factors and any biases in application and measurement technique effects associated with individual experiments. This analysis has helped to improve our understanding of key factors of NH 3 and N 2 O EFs for inclusion within models. With more studies over time, insights into the underlying processes influencing emissions will be further improved., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

According to the available guidelines, good practices for calculating nitrous oxide (N 2 O) 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 N 2 O 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 gN 2 O-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 N 2 O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (N 2 O). Previous meta-analyses have linked various biochemical properties of crop residues to N 2 O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N 2 O emissions from specific residues. Here we combine comprehensive databases for N 2 O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N 2 O emissions. On average, crop residue incorporation increased soil N 2 O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N 2 O emissions. Crop residue effects on N 2 O emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N 2 O emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N 2 O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated N 2 O emissions, whereas mature residues with opposite characteristics had marginal effects on N 2 O. The most important crop types belonging to the immature residue group - cover crops, grasslands and vegetables - are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high N 2 O emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH 3 ) and nitrous oxide (N 2 O) emissions. Using data on NH 3 and N 2 O emissions following land-applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH 3 data represent emissions from cattle and swine manures in temperate wet climates, and the N 2 O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH 3 EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH 3 -N kg -1 total N (TN), respectively, whereas the NH 3 EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low-emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N 2 O-N kg -1 TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N 2 O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N 2 O-N kg -1 TN, respectively, which were three times greater than for dry climates. The N 2 O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45-63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed., (© 2021 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Nitrous oxide (N 2 O), ammonia (NH 3 ), and methane (CH 4 ) emissions from the manure management chain of livestock production systems are important contributors to greenhouse gases (GHGs) and NH 3 emitted by human activities. Several studies have evaluated manure-related emissions and associated key variables at regional, national, or continental scales. However, there have been few studies focusing on the drivers of these emissions using a global dataset. An international project was created (DATAMAN) to develop a global database on GHG and NH 3 emissions from the manure management chain (housing, storage, and field) to identify key variables influencing emissions and ultimately to refine emission factors (EFs) for future national GHG inventories and NH 3 emission reporting. This paper describes the "field" database that focuses on N 2 O and NH 3 EFs from land-applied manure and excreta deposited by grazing livestock. We collated relevant information (EFs, manure characteristics, soil properties, and climatic conditions) from published peer-reviewed research, conference papers, and existing databases. The database, containing 5,632 observations compiled from 184 studies, was relatively evenly split between N 2 O and NH 3 (56 and 44% of the EF values, respectively). The N 2 O data were derived from studies conducted in 21 countries on five continents, with New Zealand, the United Kingdom, Kenya, and Brazil representing 86% of the data. The NH 3 data originated from studies conducted in 17 countries on four continents, with the United Kingdom, Denmark, Canada, and The Netherlands representing 79% of the data. Wet temperate climates represented 90% of the total database. The DATAMAN field database is available at http://www.dataman.co.nz., (© 2020 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Terrestrial ecosystems, both natural ecosystems and agroecosystems, generate greenhouse gases (GHGs). The chamber method is the most common method to quantify GHG fluxes from soil-plant systems and to better understand factors affecting their generation and mitigation. The objective of this study was to review and synthesize literature on chamber designs (non-flow-through, non-steady-state chamber) and associated factors that affect GHG nitrous oxide (N 2 O) flux measurement when using chamber methods. Chamber design requires consideration of many facets that include materials, insulation, sealing, venting, depth of placement, and the need to maintain plant growth and activity. Final designs should be tailored, and bench tested, in order to meet the nuances of the experimental objectives and the ecosystem under study while reducing potential artifacts. Good insulation, to prevent temperature fluctuations and pressure changes, and a high-quality seal between base and chamber are essential. Elimination of pressure differentials between headspace and atmosphere through venting should be performed, and designs now exist to eliminate Venturi effects of earlier tube-type vent designs. The use of fans within the chamber headspace increases measurement precision but may alter the flux. To establish best practice recommendations when using fans, further data are required, particularly in systems containing tall plants, to systematically evaluate the effects that fan speed, position, and mixing rate have on soil gas flux., (© 2020 The Authors. Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Adequately estimating soil nitrous oxide (N 2 O) emissions using static chambers is challenging due to the high spatial variability and episodic nature of these fluxes. We discuss how to design experiments using static chambers to better account for this variability and reduce the uncertainty of N 2 O emission estimates. This paper is part of a series, each discussing different facets of N 2 O chamber methodology. Aspects of experimental design and sampling affected by spatial variability include site selection and chamber layout, size, and areal coverage. Where used, treatment application adds a further level of spatial variability. Time of day, frequency, and duration of sampling (both individual chamber closure and overall experiment duration) affect the temporal variability captured. We also present best practice recommendations for chamber installation and sampling protocols to reduce further uncertainty. To obtain the best N 2 O emission estimates, resources should be allocated to minimize the overall uncertainty in line with experiment objectives. Sometimes this will mean prioritizing individual flux measurements and increasing their accuracy and precision by, for example, collecting four or more headspace samples during each chamber closure. However, where N 2 O fluxes are exceptionally spatially variable (e.g., in heterogeneous agricultural landscapes, such as uneven and woody grazed pastures), using available resources to deploy more chambers with fewer headspace samples per chamber may be beneficial. Similarly, for particularly episodic N 2 O fluxes, generated for example by irrigation or freeze-thaw cycles, increasing chamber sampling frequency will improve the accuracy and reduce the uncertainty of temporally interpolated N 2 O fluxes., (© 2020 The Authors. Journal of Environmental Quality © 2020 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

Nitrous oxide (N 2 O) emission from agricultural soils represents a significant source of greenhouse gas to the atmosphere. We evaluated the suitability of a modified Soil and Water Assessment Tool (SWAT) model to estimate the N 2 O flux from the application of solid manure at two grassland sites (North Wyke [NW] and Pwllpeiran [PW]) in the United Kingdom. The simulated N 2 O emissions were validated against field observations measured in 2011 and 2012 for model calibration and validation, respectively. The SWAT model predicts water-filled pore space (WFPS) very well with Nash-Sutcliffe efficiency (NSE), R 2 , RMSE, and percentage bias (PBIAS) values of 0.67, .72, 0.06, and 3.64, respectively, during the calibration period for NW site, whereas it gives 0.68, .69, 0.07, and 3.04, respectively during the validation period. At PW, the model predicted the NSE, R 2 , RMSE, and PBIAS of 0.55, .69, 0.04, and -4.5, respectively, during calibration and 0.63, .71, 0.05, and -2.6, respectively, during the validation period. Compared with WFPS, the model resulted in a slightly lower fit for N 2 O emissions for NW (NSE = 0.47, R 2  = .63 during calibration, and NSE = 0.55, R 2  = .58 during validation) and for PW (NSE = 0.54, R 2  = .71 for calibration, and NSE = 0.47, R 2  = .69 for validation). Results revealed that the SWAT model performed reasonably well in representing the dynamics of N 2 O emissions after solid manure application to grassland., (© 2020 The Authors. Journal of Environmental Quality © 2020 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.)

The properties of agricultural soils in various regions of the world are variable and can have a significant but poorly understood impact on soil nitrogen (N) transformations and nitrous oxide (N 2 O) emissions. For this reason, we undertook a study of gross N transformations and related N 2 O emissions in contrasting agricultural soils from China and the UK. Seven Chinese and three UK agricultural soils were collected for study using a 15 N tracing approach. The soil pH ranged from 5.4 to 8.7, with three acidic soils collected from Jinjing, Lishu and Boghall; one neutral soil collected from Changshu, and the other six alkaline soils collected from Quzhou, Zhangye, Changwu, Jinzhong, Boxworth and Stetchworth. Our results showed that the main N transformation processes were oxidation of ammonium (NH 4 + ) to nitrate (NO 3 - ) (O NH4 ), and mineralization of organic N to NH 4 + . The gross autotrophic nitrification rates calculated in the three acidic soils were between 0.25 and 4.15 mg N kg -1  d -1 , which were significantly lower (p < 0.05) than those in the remaining neutral and alkaline soils ranging from 6.94 to 14.43 mg N kg -1  d -1 . Generally, soil pH was positively correlated (p < 0.001) with gross autotrophic nitrification rate and cumulative N 2 O emissions, indicating that soil pH was an important factor regulating autotrophic nitrification and N 2 O emissions. There was also a significant positive correlation between the gross autotrophic nitrification rate and cumulative N 2 O emissions, highlighting the importance of this process for producing N 2 O emissions in these agricultural soils under aerobic conditions. Gross NH 4 + immobilization rates were very low in most soils except for the Jinjing soil with the lowest pH. In conclusion, the gross autotrophic nitrification rates and related N 2 O emissions were controlled by soil pH irrespectively of the soil's origin in these agricultural soils., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Intensification of grasslands is necessary to meet the increasing demand of livestock products. The application of nitrogen (N) on grasslands affects the N balance therefore the nitrogen use efficiency (NUE). Emissions of nitrous oxide (N 2 O) are produced due to N fertilisation and low NUE. These emissions depend on the type and rates of N applied. In this study we have compiled data from 5 UK N fertilised grassland sites (Crichton, Drayton, North Wyke, Hillsborough and Pwllpeiran) covering a range of soil types and climates. The experiments evaluated the effect of increasing rates of inorganic N fertiliser provided as ammonium nitrate (AN) or calcium ammonium nitrate (CAN). The following fertiliser strategies were also explored for a rate of 320 kg N ha -1 : using the nitrification inhibitor dicyandiamide (DCD), changing to urea as an N source and splitting fertiliser applications. We measured N 2 O emissions for a full year in each experiment, as well as soil mineral N, climate data, pasture yield and N offtake. N 2 O emissions were greater at Crichton and North Wyke whereas Drayton, Hillsborough and Pwllpeiran had the smallest emissions. The resulting average emission factor (EF) of 1.12% total N applied showed a range of values for all the sites between 0.6 and 2.08%. NUE depended on the site and for an application rate of 320 kg N ha -1 , N surplus was on average higher than 80 kg N ha -1 , which is proposed as a maximum by the EU Nitrogen Expert Panel. N 2 O emissions tended to be lower when urea was applied instead of AN or CAN, and were particularly reduced when using urea with DCD. Finally, correlations between the factors studied showed that total N input was related to Nofftake and Nexcess; while cumulative emissions and EF were related to yield scaled emissions., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

Urine patches and dung pats from grazing livestock create hotspots for production and emission of the greenhouse gas, nitrous oxide (N 2 O), and represent a large proportion of total N 2 O emissions in many national agricultural greenhouse gas inventories. As such, there is much interest in developing country specific N 2 O emission factors (EFs) for excretal nitrogen (EF 3, pasture, range and paddock) deposited during gazing. The aims of this study were to generate separate N 2 O emissions data for cattle derived urine and dung, to provide an evidence base for the generation of a country specific EF for the UK from this nitrogen source. The experiments were also designed to determine the effects of site and timing of application on emissions, and the efficacy of the nitrification inhibitor, dicyandiamide (DCD) on N 2 O losses. This co-ordinated set of 15 plot-scale, year-long field experiments using static chambers was conducted at five grassland sites, typical of the soil and climatic zones of grazed grassland in the UK. We show that the average urine and dung N 2 O EFs were 0.69% and 0.19%, respectively, resulting in a combined excretal N 2 O EF (EF 3 ), of 0.49%, which is <25% of the IPCC default EF 3 for excretal returns from grazing cattle. Regression analysis suggests that urine N 2 O EFs were controlled more by composition than was the case for dung, whilst dung N 2 O EFs were more related to soil and environmental factors. The urine N 2 O EF was significantly greater from the site in SW England, and significantly greater from the early grazing season urine application than later applications. Dycandiamide reduced the N 2 O EF from urine patches by an average of 46%. The significantly lower excretal EF 3 than the IPCC default has implications for the UK's national inventory and for subsequent carbon footprinting of UK ruminant livestock products., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Grazed grassland systems are an important component of the global carbon cycle and also influence global climate change through their emissions of nitrous oxide and methane. However, there are huge uncertainties and challenges in the development and parameterisation of process-based models for grazed grassland systems because of the wide diversity of vegetation and impacts of grazing animals. A process-based biogeochemistry model, DeNitrification-DeComposition (DNDC), has been modified to describe N(2)O emissions for the UK from regional conditions. This paper reports a new development of UK-DNDC in which the animal grazing practices were modified to track their contributions to the soil nitrogen (N) biogeochemistry. The new version of UK-DNDC was tested against datasets of N(2)O fluxes measured at three contrasting field sites. The results showed that the responses of the model to changes in grazing parameters were generally in agreement with observations, showing that N(2)O emissions increased as the grazing intensity increased., (Copyright © 2011 Elsevier Ltd. All rights reserved.)