N 2O emissions from different land uses in mid-subtropical China

Abstract

Agricultural soils are primarily responsible for the global anthropogenic nitrous oxide (N 2O) emissions due to excessive use of N fertilizers. Along with fertilizer, it may also be excelled by the seasonal precipitation pattern of monsoon climate in Southern China. To estimate N 2O emissions of native and agricultural soils in subtropical ecosystem surrounding Three Gorges Dam, a 4 years campaign was started to determine the temporal N 2O fluxes from seven sites of four land use types (one vegetable field, three uplands, two orchards and one pine forest). The mean annual budget of N 2O emissions was 0.13–5.27 kg N 2O-N ha −1 year −1. Pine forest had significantly lower N 2O emissions than agriculture land uses. Tilled orchard had significantly lower N 2O emissions than non-tilled orchard. Generally, among agriculture land uses, maximum N 2O emissions were observed from vegetable field followed by orchards and uplands. Among all land uses, N 2O emissions were significantly correlated with amount of N fertilizer applied. Every year, the climate was warm and wet from April through September (the hot–humid season) and became cool and dry from October through March (the cool–dry season). N 2O fluxes and environmental variables (soil temperature, water-filled pore space (WFPS), soil NO 3 −-N and NH 4 +-N contents) had significant seasonal variabilities. Driven by seasonality of soil temperature, WFPS, soil NO 3 −-N and NH 4 +-N contents, N 2O fluxes were significantly higher in the hot–humid season than in the cool–dry season. The relationship between N 2O fluxes and all the environmental variables were presented in one linear model of variation which explained 72–97% of N 2O flux variability among different land uses. We conclude that N 2O fluxes from different land uses are strongly under control of different climatic predictors along with soil nutrient status, which interact in conjunction with each other to supply the readily available substrates for the N 2O flux from the subtropical soils.