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Agricultural soils receiving synthetic fertilizers and organic amendments containing nitrogen contribute a large part to anthropogenic nitrous oxide (N 2 O) emissions. As a source of nitrate that undergoes reduction to N 2 O, organic amendments also change soil C availability and redox potential, which influences the N 2 O emission factor (EF) of organically-amended soils. The objective of this study was to conduct a meta-analysis of N 2 O EF from agricultural soils receiving organic amendments. A global survey of peer-reviewed literature resulted in the selection of 38 studies including 422 observations at 43 sites in 12 countries. The analysis yielded a global EF for all organic sources, EForg, equal to 0.57 ± 0.30%, which is lower than the IPCC default EF of 1 for synthetic fertilizers. Three groups of organic amendments with similar EFs were identified: the high-risk group including animal slurries, waste waters and biosolids (1.21 ± 0.14%); the medium-risk group including solid manure, composts + fertilizers, and crop residues + fertilizers (0.35 ± 0.13%); and the low-risk group including composts, crop residues, paper mill sludge and pellets (0.02 ± 0.13%). The EF was higher when soils received organic amendments in combination with synthetic fertilizers, such as liquid manures + fertilizers (2.14 ± 0.53%), composts + fertilizers (0.37 ± 0.24%), and crop residues + fertilizers (0.59 ± 0.27%). The EF was modulated by amendment (C/N ratio), soil (texture, drainage, organic C and N) and climatic (precipitation) factors. For example, EFs were on average 2.8 times greater in fine-textured than coarse-textured soils. We recommend site-specific EFs that consider organic amendment chemistry, soil characteristics, climate conditions and whether the organic amendment is applied alone or in combination with synthetic fertilizers. [ABSTRACT FROM AUTHOR]

Mid-season drainage (MSD) decreases methane emission from an irrigated rice paddy. For this reason, the 2006 IPCC Guidelines and several methane estimation models consider MSD as a static input factor. However, if rainfall occurs during the MSD period, the reduction effect on methane emission may become small. In this paper, we report the methane emission from an intermittently irrigated rice paddy with MSD for three growing seasons. Methane flux was measured using eddy covariance technique with an open-path methane analyzer. Our objective is to ascertain the seasonal and interannual variations in methane emission caused by rainfalls during the MSD period. The growing season (from June to Oct.) methane emission during the three year study period ranged from 198 to 450 kg CH 4 ha −1 , showing significant interannual variability with changes in rainfall during the MSD period. In order to implement the effect of rainfall during the MSD on methane emission (not considered in the IPCC method), we developed a simple method for a scaling factor. The estimated and the observed CH 4 emissions agreed within 40%, and additional consideration of soil pH further improved the agreement within 10%. These results suggest that the rainfall effect should be considered when estimating national or global methane emission from irrigated rice paddies. [ABSTRACT FROM AUTHOR]

• Emission factor and eddy covariance derived annual N 2 O budgets were comparable. • Seasonal variabilities were not adequately expressed by emission factors. • Nitrogen excretion from supplementary feed contributed to annual N 2 O emissions. • Low magnitude fluxes made up 76% of total N 2 O measured by eddy covariance. • Eddy covariance measurements resulted in a N 2 O emission factor of 1.57%. Estimates of regional and national nitrous oxide (N 2 O) emissions rely on emission factors (EFs) commonly derived from measurements using static chambers. These measurements can include high uncertainties and might obscure the quantification of N 2 O fluxes. Advances in micrometeorological eddy covariance technique (EC) now allow direct measurements of N 2 O fluxes at the field scale. Here, we compared N 2 O emissions calculated from site-specific EFs with N 2 O flux data derived from year-round EC measurements on an intensively grazed dairy pasture in the Waikato region, NZ. Annual N 2 O emissions of 7.30 kg N 2 O-N ha−1 yr−1 determined using gap-filled EC flux data were greater than N 2 O estimates of 3.82 kg N 2 O-N ha−1 yr−1 based on site-specific EFs for cattle urine (1.53%), cattle dung (0.24%) and urea fertiliser (0.16%). Likely reasons for this difference were that the EF approach did not take into account the seasonal variability of EFs, the effect of supplementary feed on cattle nitrogen (N) excretion and background N 2 O emissions (BNE). Including calculated emissions from supplementary feed N (0.92 kg N 2 O-N ha−1 yr−1) and BNE (1.09 kg N 2 O-N ha−1 yr−1) increased annual EF-based emissions to 5.83 kg N 2 O-N ha−1 yr−1. The site-specific EFs were established in spring 2017 and may not have adequately represented summer, winter and particularly autumn N 2 O emissions. The EF approach, therefore, did not fully account for the seasonal variability of N 2 O fluxes as measured by EC but, if quantified, could have led to further agreement between measurements. Using EC measurements to complement static chambers and EF approaches altered annual N 2 O emissions estimates from intensively grazed pastoral land. Hence, we conclude that N 2 O budgets derived from EFs need to better capture the effect of seasonal variability, supplementary feed and BNE. [ABSTRACT FROM AUTHOR]