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This study determined the nitrous oxide emission factors (EF1, the percentage of N2O emitted as a proportion of fertiliser N applied) for fertilisers ammonium sulphate (AS), diammonium phosphate (DAP), and urea under the same field conditions. Trials were conducted on pasture soils across four sites (Waikato, Manawatu, Canterbury and Otago) in New Zealand during late autumn and spring of 2022. The average EF1 values for urea across all four sites were 0.128% (95% C.I., 0.023% and 0.249%) in late autumn and 0.136% (95% C.I., 0.031% and 0.259%) in spring. The corresponding EF1 values for AS were 0.125% (95% C.I., – 0.021% and 0.246%) in late autumn and 0.083% (95% C.I., 0.015% and 0.197%) in spring, while for DAP, they were 0.049% (95% C.I., – 0.044% and 0.157%) in late autumn and 0.090% (95% C.I., -0.009% and 0.205%) in spring. The mean EF1 values across all four sites and two seasons were calculated as 0.132% (95% C.I., 0.016% and 0.269%) for urea, 0.104% (95% C.I., – 0.008% and 0.235%) for AS, and 0.069% (95% C.I., – 0.036 and 0.194) for DAP. No significant differences in EF1 were observed between the three fertilisers (P > 0.05) at individual sites or when considering all four sites collectively. [ABSTRACT FROM AUTHOR]

A field experiment was conducted in a subtropical tea (Camellia sinensis (L.) O. Kuntze) plantation in Jiangsu Province, China, including the following treatments: no nitrogen (N) fertilizer (control), conventional mineral N fertilizer (urea) (CN), soybean cake fertilizer (SF), pig manure (PM), cattle manure (CaM), chicken manure (CM), and CM + biochar (CMB). Cumulative nitrous oxide (N2O) and nitric oxide (NO) emissions were 4.8 ± 0.1 and 3.7 ± 0.3 kg N ha−1 year−1 under CN, respectively, and increased to 5.4 ± 0.2 and 4.6 ± 0.3 kg N ha−1 year−1 under SF (P < 0.05), respectively. Treatments with livestock manures (PM, CaM, and CM) reduced N2O (41.4–49.6%) and NO (46.5–59.8%) emission in comparison to CN. Combined amendment of CM and biochar more effectively reduced N2O emissions than CM treatment alone. Based on a meta-analysis of 26 global paired measurements in acid soils, the threshold of C/N ratios of organic fertilizers between the positive and negative responses of N2O emissions to organic fertilizers was 8.6 with a range of 4.5–22.3 (95% confidence interval), indicating that reduced N2O emission under PM, CaM and CM was potentially due to their C/N ratios compared to the threshold. Organic fertilizer application did not influence tea yield, while combined application of CM and biochar increased tea yield and resulted in the least yield-scaled N2O emission. N2O and NO emission factors for N fertilizers applied under CN were 1.9 ± 0.1% and 1.5 ± 0.2%, respectively, and reduced to 0.08 ± 0.04% and 0.12 ± 0.04% under CMB, respectively. The results suggest that tea plantations in the subtropical region are hotspots for N2O and NO emissions. Combined application of chicken manure and biochar could mitigate N gas emissions and increase yield in the tea plantation systems. [ABSTRACT FROM AUTHOR]

Abstract Calculated N 2 O emission factors (EFs) of applied nitrogen (N) fertilizer are currently based upon a single, universal value advocated by the IPCC (Inter-governmental Panel on Climate Change) even though EFs are thought to vary with climate and soil types. Here, we compiled and analyzed 151 N 2 O EF values from agricultural fields across China. The EF of synthetic N applied to these croplands was 0.60%, on average, but differed significantly among six climatic zones across the country, with the highest EF found in the north subtropical zone for upland fields (0.93%) and the lowest in the middle subtropical zone for paddy fields (0.20%). Precipitation and soil pH, which showed non-linear relationships with EF, are among the factors governing it, explaining 7.0% and 8.0% of the regional variation in EFs, respectively. Annual precipitation was the key factor regulating N 2 O emissions from synthetic N fertilizers. Among crop types, legume crops had the highest EFs, which were significantly (P < 0.05) higher than those of cereals. Total soil N 2 O emissions from fertilized croplands with maize, rice, wheat, and vegetables in China, calculated using the climatic zone (regional) EFs, were estimated to be 239 Gg N yr−1 with an uncertainty of 21%. Importantly, this value was substantially (33%) lower than that (357 Gg N yr−1) derived from the IPCC default EF but close to the 253 Gg N yr−1 estimated using crop-specific EFs. N 2 O emissions from applied synthetic N fertilizer accounted for 66.5% of the total annual N 2 O emissions from China's maize, rice, wheat and vegetable fields. Taken together, our study's results strongly suggest that regional EFs should be included for accurate N 2 O inventories from croplands across China. Graphical abstract Unlabelled Image Highlights • Croplands in China had a mean soil nitrous oxide emission factor of 0.60%. • This emission factor (EF) from China's croplands varied among climatic zones. • Precipitation and soil pH contributed significantly for regional EFs variation. • IPCC's default EF would overestimates N 2 O emissions from China's croplands. • The relationship of EF to soil and climatic variables was non-linear (quadratic). [ABSTRACT FROM AUTHOR]

Highlights: [•] We determined N2O emission factors (EF3) for animal excreta in grazed hill land. [•] There were large variations in EF3 between years and between four regions. [•] Sheep urine EF3 in low slopes (0–12°) was greater than in medium slopes (12–25°). [•] EF3 values for sheep dung and beef cattle dung were not significantly different. [•] The IPCC methodology is likely to overestimate N2O emissions from grazed hill land. [ABSTRACT FROM AUTHOR]

Abstract: The largest source of nitrous oxide (N2O) in New Zealand is excreta deposited by farmed, grazing ruminants. A country-specific excreta N2O emission factor (EF3PRP) of 1% is used to estimate these emissions. The aim of this study was to assess if disaggregation of EF3PRP by excreta type (urine vs. dung) is warranted. Cattle urine and dung was applied separately onto small plots of six different pastoral soils (well- and poorly-drained) across three climatic regions in New Zealand during two seasons (autumn and spring). Sheep dung was applied to other plots as a contrasting excreta type. N2O emissions were measured using static chambers. The average EF3PRP for cattle urine was 0.29% of the N applied, which was significantly greater than for cattle dung (0.04%) and sheep dung (0.01%). Drainage class did not always relate to soil water content and associated N2O emissions in the top soil, suggesting care is required when calculating national inventories based on soil drainage classes and their associated EF3PRP values. These results support the disaggregation of New Zealand''s EF3PRP into urine and dung emission factors. However, further disaggregation of dung EF3PRP by animal type (cattle vs. sheep) is not justified, but further research is warranted. [Copyright &y& Elsevier]

A field experiment was conducted to evaluate the influence of the continuous application of organic and mineral N fertilizer on N2O and NO emissions under maize and wheat rotation on the North China Plain. This study included eight treatments: no fertilizer (control); mineral N fertilizer (Nmin) at a rate of 200 kg N ha−1 per season; 50% mineral fertilizer N plus 50% cattle manure N (50% CM), 50% chicken manure N (50% FC) or 50% pig manure N (50% FP); 75% mineral fertilizer N plus 25% cattle manure N (25% CM), 25% chicken manure N (25% FC) or 25% pig manure N (25% FP). The annual N2O and NO emissions were 2.71 and 0.39 kg N ha−1, respectively, under the Nmin treatment, with an emission factor of 0.50% for N2O and 0.07% for NO. Compared with the Nmin treatment, N2O emissions did not differ when 50% of the mineral N was replaced with manure N (50% CM, 50% FC and 50% FP), while annual NO emissions were significantly reduced by 49.0% and 27.8% under 50% FC and 50% FP, respectively. In contrast, annual N2O emissions decreased by 21–38% compared to the Nmin treatment when 25% of the mineral N was replaced with manure N (25% CM, 25% FC and 25% FP). Most of the reduction occurred during the maize season. The 25% CM, 25% FC and 25% FP treatments had no effect on NO emissions compared to the Nmin treatment. There was no obvious difference in annual N2O and NO emissions among the organic manures at the same application rate, probably due to their similar C/N ratio. Replacing a portion of the mineral fertilizer N with organic fertilizer N did not significantly affect crop grain yield, except for the 50% FC treatment in the wheat season. Overall, the results suggest that the combined application of 25% organic manure N plus 75% mineral fertilizer N had the most potential to mitigate N2O emissions while not affecting crop yield in the maize and wheat rotation system in this area of China. [ABSTRACT FROM AUTHOR]

Abstract: Nitrous oxide (N2O) fluxes were measured over a 3-year period (2004–2007) in a long-term experimental field. The objectives of the study were to evaluate the interannual variation of N2O emissions from a maize–wheat rotation, under different fertilizer regimes and to determine the key controlling factors. The study involved four treatments: compost (OM), half compost N plus half inorganic fertilizer-N (HOM), inorganic fertilizer-N (NPK), and control (CK) where no N application. The mean annual N2O emission over a 3-year period was 0.30 ± 0.11 kg N2O–N ha−1 in the CK treatment, but increased to 1.61 ± 0.10 kg N2O–N ha−1 in the HOM treatment, 2.13 ± 0.15 kg N2O–N ha−1 in the OM treatment, and 2.76 ± 0.19 kg N2O–N ha−1 in the NPK treatment. Differences were significant among treatments. The N2O emission factors of the applied OM, NPK and HOM were 0.61 ± 0.02, 0.82 ± 0.10 and 0.44 ± 0.04%, respectively, at a rate of 300 kg N ha−1 year−1, indicating that the combined application of compost with inorganic fertilizer significantly reduced N2O emission. Over a maize–wheat rotation year, more than 65% of the annual N2O emission occurred during the maize growing season. There was a large interannual variation in N2O emission in all treatments, albeit not significant either during the maize growing season or at an inter-year scale. This interannual variation was mainly attributable to differences in soil moisture after basal fertilizer application, and irrigation and/or heavy rainfall events immediately following basal fertilization could induce more N2O production than pre-irrigation before plowing. The HOM treatment had higher N fertilizer use efficiency and lowest yield-scaled N2O emissions compared with the OM and NPK treatments. We therefore argue that the combined application of half compost N plus half fertilizer-N will mitigate N2O emissions from soils in the North China plain. [Copyright &y& Elsevier]