An inventory of N2O emissions from agriculture in China using precipitation-rectified emission factor and background emission

Fertilized agricultural soils are a major anthropogenic source of atmospheric N2O. A credible national inventory of agricultural N2O emission would benefit its global strength estimate. We compiled a worldwide database of N2O emissions from fertilized fields that were consecutively measured for more than or close to one year. Both nitrogen input (N) and precipitation (P) were found to be largely responsible for temporal and spatial variabilities in annual N2O fluxes (N2O–N). Thus, we established an empirical model (N2O–N = 1.49 P + 0.0186 P · N), in which both emission factor and background emission for N2O were rectified by precipitation. In this model, annual N2O emission consists of a background emission of 1.49 P and a fertilizer-induced emission of 0.0186 P · N. We used this model to develop a spatial inventory at the 10 × 10 km scale of direct N2O emissions from agriculture in China. N2O emissions from rice paddies were separately quantified using a cropping-specific emission factor. Annual fertilizer-induced N2O emissions amounted to 198.89 Gg N2O–N in 1997, consisting of 18.50 Gg N2O–N from rice paddies and 180.39 Gg N2O–N from fertilized uplands. Annual background emissions and total emissions of N2O from agriculture were estimated to be 92.78 Gg N2O–N and 291.67 Gg N2O–N, respectively. The annual direct N2O emission accounted for 0.92% of the applied N with an uncertainty of 29%. The highest N2O fluxes occurred in East China as compared with the least fluxes in West China.