Nitrous oxide emissions and nitrate leaching from a rain-fed wheat-maize rotation in the Sichuan Basin, China

A 3-year field experiment (October 2004-October 2007) was conducted to quantify N2O fluxes and determine the regulating factors from rain-fed, N fertilized wheat-maize rotation in the Sichuan Basin, China. Static chamber-GC techniques were used to measure soil N2O fluxes in three treatments (three replicates per treatment): CK (no fertilizer); N150 (300 kg N fertilizer ha(-1) yr(-1) or 150 kg N ha(-1) per crop); N250 (500 kg N fertilizer ha(-1) yr(-1) kg or 250 kg N ha(-1) per crop). Nitrate (NO (3) (-) ) leaching losses were measured at nearby sites using free-drained lysimeters. The annual N2O fluxes from the N fertilized treatments were in the range of 1.9 to 6.7 kg N ha(-1) yr(-1) corresponding to an N2O emission factor ranging from 0.12 % to 1.06 % (mean value: 0.61 %). The relationship between monthly soil N2O fluxes and NO (3) (-) leaching losses can be described by a significant exponential decaying function. The N2O emission factor obtained in our study was somewhat lower than the current IPCC default emission factor (1 %). Nitrate leaching, through removal of topsoil NO (3) (-) , is an underrated regulating factor of soil N2O fluxes from cropland, especially in the regions where high NO (3) (-) leaching losses occur.