環境汚染と気候変動

抽象的な

Nitrous Oxide Emissions from Household Vegetable Fields in the Rural Residential Areas of Hilly Subtropical Central China

Xiaoqing Fu, Yong Li, Yi Wang, Jianlin Shen, Runlin Xiao, Dan Chen and Jinshui Wu

Nitrous oxide (N₂O) emissions from a household vegetable field in a rural residential area of hilly subtropical central China were observed using a static chamber-gas chromatographic method from January 2010 to December 2011. The N₂O fluxes exhibited seasonal dynamics and the accumulated N₂O emissions during the wet seasons accounted for 83.5% of the total N₂O emissions. Soil mineral nitrogen (N) contents were found not limiting factors because of the application of large amounts of human excreta. The daily N₂O fluxes showed a significant, positive correlation with soil temperature, soil moisture and soil NO₃ --N content, and soil denitrification may be the major pathway responsible for N₂O emissions. High-frequency, intensive application of liquid excreta stimulated the N₂O emission process. The average annual N₂O emission rate was 12.1 ± 0.9 kg N ha-1 year-1 in the examined household vegetable field, and the total N₂O emissions from household vegetable fields originating from the N source of human excreta in the studied Jinjing catchment (135 km2) were estimated as 1.58 ± 0.16 ton N year-1. Such emissions can be considered as N₂O re-emissions of the N input into the ecosystem, and the emission factor of N₂O re-emissions was estimated to be 0.57%. The findings indicated that under the present management practices, household vegetable fields in the subtropics of China provide a relevant contribution to greenhouse gas emissions and a responsive mitigation scheme at a household scale is needed to reduce N₂O emissions.