[N2O emissions from agricultural ecosystem in Sichuan-Chongqing region]

A regional nitrogen cycling model IAP-N was adopted to estimate nitrous oxide (N2O) emission from the agro-ecosystem in the Sichuan-Chongqing Region during 1990-2004. The county level agricultural activities data were used, and Sichuan-Chongqing Region was divided into four sub-areas by the geographical characteristics, environment and local climatic conditions and administrative division. The results showed that annual averaged N2O emissions (in nitrogen gauge) in 1990-1994, 1995-1999, 2000-2004, respectively, were 52.3, 58.2, 62.0 Gg/a, of which 55% came from the N2O direct emission of the fertilized croplands. They were 29.6 (7.6-63.3), 33.0 (8.4-71.8), 34.0 (8.5-75.8) Gg/a, equals to 4.73, 5.39, 6.11 kg/(hm2 x a), respectively. Upland/glebe was the primary source of the N2O direct emission. Meanwhile, paddy-upland rotation system also played an important contribution to it. The increasing rates of N2O emission from agro-ecosystem and N2O emission flux in cropland were much higher in 1995-1999 than in 1990-1994. The N2O emission flux in the cropland showed a continuous increasing trend in 2000-2004, but the increasing rates of total N2O emission from agro-ecosystem were stagnant due to the decrease of arable land area. The N2O emission of agro-ecosystem mainly came from Chengdu Plain and Chongqing. The contributions of different sources to the total N2O emission of agro-ecosystem were variable in the region. For instance, the primary source of N2O emission was the direct emission from croplands in Chengdu Plain and Chongqing, whereas, in northwest region of Sichuan province was the N2O emission induced by grazing. The results will provide a scientific basis for policy maker to make fertilizer effectively applied and mitigate GHG emission from agro-ecosystem of Sichuan-Chongqing Region.