An inventory of N(2)O emissions from agriculture in China using precipitation-rectified emission factor and background emission.

Fertilized agricultural soils are a major anthropogenic source of atmospheric N(2)O. A credible national inventory of agricultural N(2)O emission would benefit its global strength estimate. We compiled a worldwide database of N(2)O 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 N(2)O fluxes (N(2)O-N). Thus, we established an empirical model (N(2)O-N=1.49 P+0.0186 P.N), in which both emission factor and background emission for N(2)O were rectified by precipitation. In this model, annual N(2)O 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 10x10km scale of direct N(2)O emissions from agriculture in China. N(2)O emissions from rice paddies were separately quantified using a cropping-specific emission factor. Annual fertilizer-induced N(2)O emissions amounted to 198.89GgN(2)O-N in 1997, consisting of 18.50GgN(2)O-N from rice paddies and 180.39GgN(2)O-N from fertilized uplands. Annual background emissions and total emissions of N(2)O from agriculture were estimated to be 92.78GgN(2)O-N and 291.67GgN(2)O-N, respectively. The annual direct N(2)O emission accounted for 0.92% of the applied N with an uncertainty of 29%. The highest N(2)O fluxes occurred in East China as compared with the least fluxes in West China.