Development of N2o Empirical Model Linking Decomposed CO2 and N Inputs for Estimating Annual N2o Emission from Agricultural Soils in Japan.

Mitigation of greenhouse gas (GHG) emissions in agricultural sector could be achieved through improved management practices. Uncertainty about the complex biological and ecological processes involved in GHG emissions and carbon storage in agricultural soils, currently limits our ability to evaluate the persistence of mitigation practices. Particularly, N₂O emission from soils is of small magnitude and highly variable in space and time, and is thus very difficult to estimate. In the meanwhile, due to the limitation of activity data (e.g. types and amounts of chemical fertilizer, composts and manures), to estimate N₂O emission at a country scale warrant the development of N₂O model for easy estimating annual N₂O emission under variable managements with satisfied accuracy. In contrast to N₂O emission, CO₂ from the decomposition of soil organic matter is controlled primarily by soil temperature and moisture. An empirical model using soil C/N ratio and decomposed CO₂ to estimate annual or seasonal N₂O emission from upland crop fields has been developed (Mu et al., 2009). In this study, to verify this model we further collected peer-reviewed published datasets of N₂O and CO₂ emission from different N application rates with different soil types and land use categories in Japan and outside Japan. Especial emphasis was given on the performance of model predicting N₂O emission from Andisols versus non-Andisols. Furthermore, we combine the Roth-C model to this N₂O empirical model to predict annual N₂O emission and validate the results using field data from 10 sites (Andisols and non-Andisols) which only measured N₂O emission, and found that this approach is available for estimating annual N₂O emissions. Using this approach we estimated annual direct N₂O emission from agricultural soils in a region area from 1970 to 2020 and compared with IPCC Tier2 method. Our results showed that this approach can be used for the inventories of N₂O emission from agricultural soils in Japan.