Emissions of nitrous oxide (N2O) from agricultural soils can be substantial during the non-growing season (NGS; defined in Canada as November 1 to April 30) but this conclusion is supported by only limited observations. Year-round studies utilizing multi-year observations are needed to confirm NGS emission trends and link these emissions to drivers, thus enabling recommendations for improved management practices. This study addresses these needs by providing twenty years of quasi-continuous, micrometeorological observations of N2O from an agricultural field near Ottawa, Ontario, marginally gap-filled using the DeNitrification and DeComposition model (DNDCv.CAN). With these observations, we confirm two distinct N2O emission periods frequently observed at the site, each with its own environmental driver. The first occurs immediately following snowmelt (DOY 68 to 114), while the second follows N-fertilizer application (DOY 131 to 172). Nitrogen fertilization rate was the main driver of the second sustained emission event. The main driver of the spring thaw emissions was confirmed to be the number of soil cumulative freezing degree days (CFD), consistent with a previous study from other Canadian experimental sites. Although our data supported the previously published non-linear relationship of increasing NGS N2O emissions with CFD, we found that higher N2O emissions occurred under fewer CFD than previously reported. Our results show that nitrogen fertilizer application results in large, routine N2O fluxes post-application, while NGS emissions, particularly at spring snowmelt, are strongly related to CFD.

Tillage-induced soil inversion and buried residues are often overlooked in agroecosystem models, particularly when combined with manure applications. This may lead models to overestimate soil organic carbon (SOC) losses from moldboard plowing, biasing carbon accounting relative to other tillage practices. This study improved the DeNitrification DeComposition (DNDC) model to better represent moldboard and chisel plowing, with and without, manure on SOC dynamics at depth. DNDC was enhanced by incorporating soil inversion under moldboard plowing and allocating residues to deeper layers where decomposition slows. Field studies included a barley monoculture and barley-perennial forage rotation on silty clay soil at Normandin, Quebec, and a cornsoybean-wheat rotation on a sandy loam soil at Universite Laval, Quebec. At Normandin DNDC reasonably simulated barley grain and residue yields (NRMSE 18.4-47.4%) but had difficulties with interannual forage variability, likely due to winter-kill. Simulated SOC aligned with observations across fertilizer and tillage treatments (NRMSE 2.8-14.8%). DNDC captured observed trends, with manure plus barley-forage increasing SOC at deeper depths under moldboard plowing, while chisel plowing retained more SOC near the surface. At Universite Laval, DNDC effectively simulated yields (NRMSE 8.3-27.1%) and crop residues (NRMSE 8.8-29.6%), and captured surface SOC differences among treatments, with minimum tillage increasing surface SOC and moldboard plowing increasing total SOC through residue burial. DNDC showed limited sensitivity to management in deeper layers, reflecting limitations in simulating dissolved organic carbon transport. Overall, findings emphasized the importance of explicitly modelling residue burial and soil inversion as models increasingly support regional assessments and carbon credit programs.

Nitrogen (N) fertilizer supports global food production, but its use and overuse drive emissions of nitrous oxide (N _2 O), a potent and long-lived greenhouse gas. Understanding the drivers of N _2 O fluxes remains elusive, making it difficult to predict emissions in time and space and to develop and evaluate ways to lower emissions through management. Major scientific uncertainties underlying the understanding of the drivers of N _2 O fluxes identified in a workshop of N _2 O emissions experts include poor process-based understanding of controls on soil N _2 O emissions in the field; insufficient data to reduce uncertainty in N _2 O budgets from the field to regional scales, including N _2 O emission measurements and importantly, field-scale N balances; and high uncertainty in model predictions of soil N _2 O emissions across environmental and management conditions. To reduce these uncertainties, we present the concept of N _2 Onet, a global collaborative initiative to accelerate advances in N _2 O measurement, analyses, and mitigation. N _2 Onet will serve as an observational network of supersites with multi-scale measurements; a database hub for N _2 O flux and ancillary data; and a catalyst for community building, information sharing, and training. By coalescing and coordinating the global community of researchers, N _2 Onet will provide a roadmap for reducing N _2 O emissions from agriculture worldwide.

There are many fertilizer additives and alternatives that aim to increase plant nutrient use efficiency and reduce nutrient losses to the environment, here referred to collectively as enhanced efficiency fertilizers (EEFs). However, there is often insufficient published scientific field trial results across a variety of locations, climates, soils, cropping systems, and management scenarios to prove their efficacy and conditions for use. Guidelines for common minimum datasets and data stewardship in evaluating the agronomic performance and environmental impact of EEFs are needed for researchers to follow. Such guidelines will improve hypothesis testing centered on product efficacy and provide producers with guidance on how these technologies function and perform when integrated with other management practices within the 4R Nutrient Stewardship Framework. A scientific committee was formed to develop a set of protocol guidelines for evaluating EEFs in replicated, plot-based field trials on an international scale. The guidelines are composed of experimental design and core metadata, crop and soil analyses, environmental loss measurements, and data stewardship, and include both recommended and required components to allow for flexibility and adaptability depending on the trial location, objectives, infrastructure capacity, product type, and depth of understanding of the potential EEF efficacy. This approach will ensure consistency and compatibility in experimental design and data collection to support data integration, analysis, and reuse leading to large-scale impact and end-user confidence.

In the past decades, dairy farms in eastern Canada have dedicated more land to annual crops and less to perennial forages. Concurrently, there has been a shift in cattle manure management from solid to liquid forms. Our objective was to determine the early response of soil health indicators (soil aggregate stability to water, carbon [C] and nitrogen [N] in microbial biomass, particulate organic matter, and nonfractionated soil) to two crop types (annual crops vs. perennial forages) and N sources (mineral fertilizer, dairy cattle slurry, and biological N fixation) in the 0-10 cm surface soil at three locations (Ontario, Quebec, and Nova Scotia). Despite some variability in their response, most of the indicators pointed to an improvement in soil health within three years of implementation of perennial forages and/or dairy cattle slurry applications. Particulate organic matter and microbial biomass were generally more responsive to the experimental treatments than soil organic matter. Changes in soil C and N were found at the three locations within the first three years of the experiment. For instance, C concentrations were 7%-31% higher under perennial forages and/or dairy cattle slurry in comparison to annual cropping and/or mineral fertilization. Improvement in soil health was generally greater under perennial forages fertilized with dairy cattle slurry, than under annual crops receiving mineral fertilizer. The response of soil C concentration tended to be more pronounced at sites with lower initial soil C concentrations, and faster in the soil with the highest clay content.

Greenhouse gas (GHG) emissions from wild lowbush blueberry (WLB) production after fertilization with conventional mineral (MIN) and organic (ORG) or industrial pulp and paper mill sludge (PPMS) and synthetic anhydrite (SA; calcic amendment; CaSO4) remain unknown. We assessed nitrous oxide (N2O) and methane (CH4) emissions following application of combined PPMS and SA under WLB production compared to MIN and ORG fertilizers during a two-year cropping cycle. A 50 kg nitrogen (N) ha-1 recommended input was broadcasted before stem emergence during the pruning phase with MIN, ORG, and PPMS treatments alongside an unfertilized control (0 N; CTL). The PPMS treatment was also combined with SA as 6 Mg ha-1 (1SA) and 12 Mg ha-1 (2SA) inputs, which were also applied alone for a total of eight treatments. The GHG emissions were monitored using non-flow-through, non-steady-state chambers during two growing seasons. The N2O and CH4 emissions were unaffected by fertilizer applications. The N2O emissions were significantly higher during the pruning phase (0.06 f 0.009 kg N2O-N ha-1 yr-1) than during the harvesting phase (0.03 f 0.005 kg N2O-N ha-1 yr-1). The fertilizer-induced emission factor (FIEF) values (-0.01 f 0.02 %) were much lower than the default 1 % used for GHG inventories. A CH4 uptake was observed during both growing seasons, with higher uptake during the pruning phase (-2.1 f 0.1 kg CH4-C ha-1 yr-1) than in the harvesting phase (-1.6 f 0.1 kg CH4-C ha-1 yr-1). High aeration of sandy soils combined with low soil NO3 contents (0.9 mu g NO3-N cm-2 yr-1 during the pruning phase) might constrain N2O emissions. Proposed WLB-specific FIEF should be used in future GHG inventories to prevent emission overestimates. Further research is needed on the agronomic benefits and yield effects of combining PPMS and SA for WLB productivity.

Urease and nitrification inhibitors can reduce ammonia and greenhouse gas emissions from fertilizers and manure but their effectiveness depends on the conditions under which they are used. Consequently, it is essential for the credibility of emission reductions reported in regulatory emission inventories that their effectiveness is assessed under real-world conditions and not just in the laboratory. Here, we specify the criteria we consider necessary before the effects of inhibitors are included in regulatory emission inventories.

Minimizing tillage has been promoted as an agricultural practice that may mitigate greenhouse gas emissions through carbon sequestration. However, there is some ambiguity regarding the effect of minimum tillage (MT) on emissions of other greenhouse gases, in particular soil nitrous oxide (N2O) emissions. To determine how effective MT could be in helping Canada mitigate greenhouse gas emissions, we used a meta-analysis to compare growing season N2O emissions from MT versus conventional tillage (CT). Overall, MT had 12% lower N2O emissions compared to CT ( P = 0.03). However, there was high variability due to soil texture and growing season precipitation (GSP), with MT tending to emit more N2O than CT in climates where GSP exceeded 600 mm, particularly for soils with sand content less than 60%. Therefore, unless long-term tillage trials, which are urgently needed in eastern Canada, show a reduction in N2O emissions over time, MT should be used as a greenhouse gas mitigation measure only in dry climates or on sandy soils.

Perennial forages in rotation with annual crops can improve agricultural resilience by increasing soil organic carbon. However, how nitrogen (N) sources interact with rotation diversity to influence soil nitrous oxide (N2O) emissions is not well understood. During three snow-free seasons, N2O emissions, crop yields, and ancillary variables were measured at three experimental sites with contrasting soil textures (silty clay and sandy loam) in eastern Canada. Using a split-plot design, we compared a corn (Zea mays L.)-soybean (Glycine max [L.] Merr.)-corn rotation and a mixed perennial grass sward receiving N via: i) mineral fertilizer (MIN), ii) liquid dairy manure (LDM), and iii) inclusion of alfalfa (Medicago sativa L.) to the perennial forages with no additional N (LEG). When summed across sites over all three years, cumulative N2O emissions were greater for LDM than MIN in annual crops (8.75 ± 1.63 and 5.15 ± 0.96 kg N2O-N ha–1, respectively), but not in perennial grasses (2.95 ± 0.55 and 3.76 ± 0.70 kg N2O-N ha–1, respectively). When comparing N sources within each crop type over the three years, MIN generated greater yields than LDM in annual and perennial crops, but lower yield-scaled N2O emissions than LDM in annual crops only. During forages post-seeding years, area- and yield-scaled N2O emissions induced by LDM and LEG were lower than MIN. Our results suggest that for a cool humid climate using LDM or LEG in perennial forages and MIN on annual crops can reduce overall N2O emissions, while generating similar or lower yield-scaled emissions.

Developing and implementing improved management practices are necessary to enhance the sustainability of organic cropping systems. This study examined the effects of various organic cropping systems on soil green-house gas (GHG) emissions and crop yields in Que ' bec, Canada. Organic cropping systems combining different: (i) crop sequences (barley [Hordeum vulgare L.]-grain corn [Zea mays L.], soybean [Glycine max (L.) Merr.]-spring wheat [Triticum aestivum L.], and grain corn-soybean), (ii) nitrogen (N) sources (poultry manure [PM] and/or a fall-seeded green manure [GM] or no applied N), and (iii) primary tillage intensities (moldboard plough [MP] or chisel plough [CP]) were compared to a perennial forage (PF) and a bare fallow (BF) control. During the 2019 and 2020 snow-free seasons, nitrous oxide (N2O) and methane (CH4) emissions, soil water content, soil tem-perature, and mineral N concentrations were monitored periodically on a sandy loam soil. The lowest cumulative N2O emissions were found in CP-GM (0.52 +/- 0.11 kg N ha-1 in 2019 and 0.47 +/- 0.06 kg N ha-1 in 2020), whereas the highest N2O emissions were found in MP-PM in 2019 (3.55 +/- 0.72 kg N ha-1) and BF in 2020 (1.44 +/- 0.20 kg N ha-1). For the barley-grain corn sequence, the CP-GM treatment generated N2O emissions that were 40-70 % lower and yields that were 33-51 % lower than the MP-PMGM and CP-PMGM systems, which showed equivalent N2O emissions and yields. Yield-scaled N2O emissions were equivalent for all cropping systems. Peak N2O daily fluxes in the PF occurred shortly after cutting in 2020. During both years, CH4 emissions varied from -0.65 to + 0.18 kg C ha-1 with no detectable differences among cropping systems. The CP-GM cropping system minimized area-scaled N2O emissions without increasing yield-scaled emissions. However, this was a two-year study on a site that was recently converted from conventional agriculture, so a long-term assessment is still necessary to determine whether the benefits associated with these cropping systems change over time.

National inventory reporting of agricultural nitrous oxide (N 2 O) emissions in Canada is based primarily on measurements obtained using static chambers. In regions with cold winters and an accumulated snowpack (including Canada), these measurements tend to focus on the growing season (typically May–October). However, research has shown that emissions continue throughout the non-growing season (NGS) and that these account for a significant proportion of annual emissions. In the Canadian National Inventory NGS emissions currently are assumed to be adequately captured in western Canada, while they are accounted for in eastern Canada by multiplying the growing season emissions by a correction factor of 1.4, a value that was derived based on a limited number of measurements. Here we use recent Canadian studies to validate this correction factor. We collected data from available Canadian studies that measured soil N 2 O emissions from agricultural systems for the entire year and determined the proportion of these emissions that occurred during the NGS. The proportion of annual N 2 O emissions that occurred during the NGS varied widely, ranging from −4% to 119% with a mean of 35.5%, compared to the previous estimate of 30%. Due to high variability, few differences were observed between means associated with climatic, soil, and management variables. To correct for NGS N 2 O emissions from Canadian agricultural soils, we suggest that the current correction factor for converting growing season to total annual emissions be changed from 1.4 to 1.55 and that this be used for all agricultural soils in Canada rather than just eastern Canada.

In sub-Saharan Africa, agriculture can account for up to 66% of anthropogenic greenhouse gas (GHG) emissions. Unfortunately, due to the low number of studies in the region there is still much uncertainty on how management activities can affect these emissions. To help reduce this uncertainty, we measured GHG emissions from three maize (Zea mays) growing seasons in central Kenya. Treatments included: (1) a no N application control (C); (2) split (30% at planting and 70% 1 month after planting) mineral nitrogen (N) applications (Min—100 kg N ha−1); (3) split mineral N + irrigation (equivalent to 10 mm precipitation every three days—MI); (4) split mineral N + 40 kg N ha−1 added as manure (MM—total N = 140 kg ha−1); and (5) split mineral + intercropping with faba beans (Phaseolus vulgaris—MB). Soil CO2 fluxes were lower in season 1 compared to seasons 2 and 3 with fluxes highest in Min (p = 0.02) in season 2 and lowest in C (p = 0.02) in season 3. There was uptake of CH4 in these soils that decreased from season 1 to 3 as the mean soil moisture content increased. Cumulative N2O fluxes ranged from 0.25 to 2.45 kg N2O-N ha−1, with the highest fluxes from MI during season 3 (p = 0.01) and the lowest from C during season 1 (p = 0.03). The average fertilizer induced emission factor (0.36 ± 0.03%) was roughly one-third the default value of 1%. Soil moisture was a critical factor controlling GHG emissions in these central Kenya highlands. Under low soil moisture, the soils were CH4 sinks and minimal N2O sources.

Livestock are an important source of livelihoods in agricultural systems in sub-Saharan Africa (SSA), while also being the largest source of national greenhouse gas (GHG) emissions in most African countries. As a consequence, there is a critical need for data on livestock GHG sources and sinks to develop national inventories, as well as conduct baseline measurements and intervention testing to mitigate GHG emissions and meet ambitious national climate goals. Our objective was to review studies on GHG emissions from livestock systems in SSA, as well as soil carbon storage in livestock-dominated systems (i.e., grasslands and rangelands), to evaluate best current data and suggest future research priorities. To this end, we compiled studies from SSA that determined emission factors (EFs) for enteric methane and manure emissions, along with studies on soil organic carbon (SOC) stocks in SSA. We found that there has been limited research on livestock GHG emissions and SOC relative to national ambitions for climate change mitigation in SSA. Enteric methane emission factors (EFs) in low productivity cattle systems may be lower than IPCC Tier 1 default EFs, whereas small ruminants (i.e. sheep and goats) had higher EFs compared to IPCC Tier 1 EFs. Manure EFs were equal to or lower than IPCC Tier 1 EFs for deposited manure (while grazing), manure applied as fertilizer, and manure management. SOC stocks for grasslands and rangelands in SSA show broad agreement with IPCC estimates, but there was a strong geographic bias and many studies did not report soil type, bulk density, or SOC stocks at >30 cm depth. In general, the largest data gaps included information for manure (quantity, quality, management), small ruminants, agropastoral/pastoralist systems, and in general from West Africa. Future research should focus on filling major data gaps on locally appropriate mitigation interventions and improving livestock activity data for developing Tier 2 GHG inventories in SSA. At the science-policy interface, all parties would benefit from enhanced coordination within the research community and between researchers and African governments to improve Tier 2 inventories and harmonize measurement for mitigation in livestock systems in SSA.

Livestock excreta on pastures is an important source of nitrous oxide (N2O) emissions, however studies measuring these emissions in tropical regions, particularly Africa, remain limited. Therefore we measured N2O emissions from different quantities of dung patches during three observation periods (dry, wet and transition from dry to wet season) and different volumes of urine patches during wet and dry seasons. Dung patches did not stimulate soil N2O emissions in any of the three observation periods, while urine application stimulated soil N2O emissions during both seasons, with higher emissions observed during the wet season. The dung EFs (0.00-0.03%) and the urine EFs (0.04-0.40%) showed no detectable effects of dung quantity or urine volume. We further synthesized observations from other studies in wet and dry tropical regions, which indicated that the excreta N2O EFs were similar to the default values provided in the IPCC 2019 refinement (0.11% vs 0.07% for dung and 0.41% vs 0.32% for urine in dry climates, and 0.13% vs 0.13% for dung and 0.65% vs 0.77% for urine in wet climates). However, sub-Saharan African (SSA) studies had consistently lower EFs, possibly due to the lower urine-N: dung-N ratio in SSA compared with the other tropical regions, suggesting that the refinement may still overestimate excreta emissions in SSA. Moreover, considering the large variations in the summarized tropical excreta N2O EFs, from -0.01 to 1.77% for dung and 0.00 to 4.90% for urine, more studies under diverse conditions across tropical regions are recommended.

Reduced tillage is often promoted as a method to sequester carbon (C) in soils and thus mitigate climate change. However, in certain conditions reduced tillage may increase soil nitrous oxide (N2O) fluxes, which may negate any climate gains from the potential storage of C in soil. To investigate how long-term applications of different manures interact with tillage effects on N2O fluxes during the crop rotation, we established a long-term trial 2009 in eastern Canada, using two tillage (inversion tillage [IT]; and reduced tillage [RT],) and three fertilizer types (pig slurry, dairy slurry and a 0-N control) arranged in a split-plot design with 3 replications. The experiment was reproduced on two contrasting soil textures (silty clay and sandy loam) located approximately 900 m apart in a wheat-corn-soybean rotation. During 2016 (wheat), 2017 (corn), and 2018 (soybean) we estimated the N2O fluxes from each plot using manual static chambers for the growing season (April November). Mean cumulative fluxes for the growing season ranged from 0.8 kg N2O-N ha(-1) for the corn/control/ IT to 7.6 kg N2O-N ha(-1) for the wheat/dairy slurry/RT in the silty clay soils and from 0.4 kg N2O-N ha(-1) for the corn/control/IT to 3.0 kg N2O-N ha(-1) in the corn/pig slurry/RT in the sandy loam soils. The RT increased soil N2O fluxes for both slurry types and the control in the clay soil (mean flux for all fertilizer treatments over both seasons were 5.5 and 2.4 kg N2O-N ha(-1) season(-1) for the RT and IT, respectively), likely because the higher water content in the RT caused greater denitrification; while on the sandy loam the N2O flux was similar between the two tillage systems. Manure type had no measurable effect on the growing season N2O fluxes in either soil type as both provided sufficient labile N. Application of both slurries however, resulted in greater emissions than the control (P = 0.002). These findings suggest that RT on fine-textured soils in this region may not be effective strategy to reduce GHG emissions.

Crop-livestock farms across Africa are highly variable due to in agroecological and socioeconomic factors, the latter shaping the demand and supply of livestock products. Crop-livestock farms in Africa in the 21 st century are very different from most mixed farms elsewhere in the world. African crop-livestock farms are smaller in size, have fewer livestock, lower productivity and less dependency on imported feed than farms in most countries of Europe, the Americas and the intensive agricultural systems of Asia. This paper discusses the role African crop-livestock farms have in the broader socio-agricultural economy,and how these are likely to change adapting to pressures brought on by the intensification of food systems. This intensification implies increasing land productivity（more food per hectare）, often leading to more livestock heads per farm,producing fertilized feeds in croplands and importing feed supplements from the market. This discussion includes（1） the links between crop yields, soil fertility and crop-livestock integration,（2） the increasing demand for livestock products and the land resources required to meet to this demand, and（3） the opportunities to integrate broader societal goals into the development of crop-livestock farms. There is ample room for development of crop-livestock farms in Africa, and keeping integration as part of the development will help prevent many of the mistakes and environmental problems related to the intensification of livestock production observed elsewhere in the world. This development can integrate biodiversity, climate change adaptation and mitigation to the current goals of increasing productivity and food security. The inclusion of broader goals could help farmers access the level of finance required to implement changes.

Countries in sub-Saharan Africa (SSA) rely on IPCC emission factors (EF) for GHG emission reporting. However, these were derived for industrialized livestock farms and do not represent conditions of smallholder farms (small, low-producing livestock breeds, poor feed quality, feed scarcity). Here, we present the first measurements of CH4 and N2O emissions from cattle-manure heaps representing feeding practices typical for smallholder farms in the highlands of East Africa: 1) cattle fed below maintenance energy requirements to represent feed scarcity, and 2) cattle fed tropical forage grasses (Napier, Rhodes, Brachiaria). Sub-maintenance feeding reduced cumulative manure N2O emissions compared to cattle receiving sufficient feed but did not change EFN2O. Sub-maintenance feeding did not affect cumulative manure CH4 emissions or EFCH4. When cattle were fed tropical forage grasses, cumulative manure N2O emissions did not differ between diets, but manure EFN2O from Brachiaria and Rhodes diets were lower than the IPCC EFN2O for solid storage (1%, 2019 Refinement of IPCC Guidelines). Manure CH4 emissions were lower in the Rhodes grass diet than when feeding Napier or Brachiaria, and manure EFCH4 from all three grasses were lower than the IPCC default (4.4 gCH4kg-1 VS, 2019 Refinement of IPCC Guidelines). Regression analysis revealed that manure N concentration and C:N were important drivers of N2O emissions, with low N concentrations and high C:N reducing N2O emissions. Our results show that IPCC EFs overestimate excreta GHG emissions, which calls for additional measurements to develop localized EFs for smallholder livestock systems in SSA.

The effort to increase the sustainable supply of food and fibre is challenged by the potential for increased greenhouse gas (GHG) emissions from farming systems with intensified production systems. This study aimed at quantifying soil N2O emissions from smallholder organic and conventional cotton production practices in a semi-arid area, Meatu, Northern Tanzania. Field experiments were conducted to quantify N2O emissions under (i) current practices with organic (3 Mg ha−1 farmyard manure (FYM)) and conventional (30 kg mineral N ha−1) cultivation; (ii) a high input practice with organic (5 Mg ha−1 FYM) and conventional (60 kg mineral N ha−1) cultivation; and (iii) an integrated practice with organic (3 Mg FYM + legume intercropping) and conventional (30 kg N + 3 Mg ha−1 FYM) cultivation. In both organic and conventional farming, control treatments with no fertilizer application were included. The study was performed over two growing seasons, where season 1 was rather wet and season 2 was rather dry. Static chambers were used for in-situ measurement of N2O emission from soil. The current organic and conventional cotton farming practices did not differ (P > 0.05) in cumulative area-scaled and yield-scaled N2O emissions. High input conventional cotton showed higher area scaled N2O emissions than organic cotton during the wetter season, but not during the drier season. The inorganic fertilizer + FYM combination did not differ (P > 0.05) in area- and yield-scaled N2O emissions from conventional practice. Intercropping cotton and legumes did not affect (P > 0.05) N2O emission compared to 3 Mg FYM ha−1. The emission factors for both conventional and organic systems were generally above 1% in the dry season 2, but below 1% in the wetter season 1. The use of organic and inorganic fertilizers at rates up to 60 kg N ha−1, FYM-inorganic fertilizer combination, and cotton-legume intercropping increased yields, while N2O emissions stayed low, in particular with use of mineral fertilizers.

Urine and dung patches deposited by grazing cattle on grassland are an important source of nitrous oxide (N2O). While a number of studies have investigated the effects of excreta on soil N2O fluxes in developed economies and in China, observations in sub-Saharan Africa (SSA) are scarce. Moreover, the effects of soil properties (e.g. pH or texture) on N2O emissions from excreta patches have hardly been studied. In this study we investigated the importance of soil properties on N2O and carbon dioxide (CO2) emissions from cattle excreta (dung, urine, and manure [dung + urine]) for five typical tropical soils in Kenya. For this, intact soil cores were translocated from Western Kenya (Nandi county) to Nairobi, where N2O and CO2 fluxes were measured over four individual periods (two during dry seasons and two during wet seasons). Fluxes were measured for between 25 and 73 days following surface application of excreta, depending on how quickly emissions returned to baseline. Both dung and manure applications led to increased CO2 and N2O fluxes during both dry and wet seasons. On average, the N2O emission factor (EF) for manure was higher than for dung. The EFs during the wet season were higher for both the dung (0.12%) and urine (0.50%) compared to the dry season EFs (0.01% and 0.07% for dung and urine respectively). Soil type had no measurable effect on N2O and CO2 emissions for either dung or manure application. In contrast, soil clay content was negatively (P < 0.05) and pH positively (P < 0.05) correlated with N2O emissions after urine application. Assuming an excreta-N ratio of dung to urine of 66:34, as evidenced in earlier studies for SSA, and averaging across all treatments and soils, we calculated a cattle excreta N2O EF of 0.14%, which is one magnitude lower than the IPCC default N2O EF of 2%. Our results call for a revision of the IPCC guidelines for calculating N2O emissions from excreta deposition on tropical rangelands.

Reducing nitrous oxide (N2O) emissions from agriculture is critical to limiting future global warming. In response, a growing number of food retailers and manufacturers have committed to reducing N2O emissions from their vast networks of farmer suppliers by providing technical assistance and financial incentives. A key challenge for such companies is demonstrating that their efforts are leading to meaningful progress toward their climate mitigation commitments. We show that a simplified version of soil surface nitrogen (N) balance-or partial N balance-the difference between N inputs to and outputs from a farm field (fertilizer N minus crop N), is a robust indicator of direct N2O emissions from fields with maize and other major rainfed temperate-region crops. Furthermore, we present a generalized environmental model that will allow food-supply-chain companies to translate aggregated and anonymized changes in average N balance across their supplying farms into aggregated changes in N2O emissions. This research is an important first step, based on currently available science, in helping companies demonstrate the impact of their sustainability efforts.