Estimating N2O Emissions from Japanese Agricultural Soils at a Country Scale Using an Empirical Modeling Approach.

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 limitation of activity data (e.g. types and amounts of chemical fertilizer, composts and manures), estimation of N₂O emission in a country scale requires the development of N₂O model for easy estimating annual N₂O emission under vary 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). We combine the Roth-C model to this N₂O empirical model to predict annual N₂O emission and validate the results using field data from ten sites (Andisols and non-Andisols) which only measured N₂O emission, and found that this approach is available for estimating annual N₂O emissions. Using this apporach we estimated annual direct N₂O emission from agricultural soils in a region area from 1970 to 2050 and compared with IPCC Tier2 method, and discussing the differences among the seven blocks over Japan. Our results showed that this approcah can be used for inventories of N₂O emission from agricultural soils in Japan.