Simulation of N2O emissions from rain-fed wheat and the impact of climate variation in southeastern Australia

Abstract

The Water and Nitrogen Management model (WNMM) was applied to simulate N2O emissions from a rain-fed wheat cropping system on a loam-textured soil for two treatments, conventional cultivation with residue burn (CC + BURN + N) and direct drill with residue retention (DD + RET + N), at Rutherglen in southeastern Australia from January 2004 to March 2005. Both treatments received the same amount of nitrogen (N) fertiliser. The WNMM satisfactorily simulated the soil water content, mineral N contents and N2O emissions from the soil, as compared with the field observations for both treatments. The simulated nitrification-induced N2O emissions accounted for 45% and 34% of total N2O emissions for the treatments CC + BURN + N and DD + RET + N, respectively. The calibrated WNMM was used to simulate N2O emissions from this soil using historic daily weather data from 1968 to 2004 and applying seven scenarios of fertiliser N application. Correlation analysis found that the annual N2O emissions for this rain-fed wheat cropping system were significantly correlated to the annual average of daily maximum air temperature (r = 0.51 for CC + BURN + N and 0.56 for DD + RET + N), annual rainfall (r = −0.56 for CC + BURN + N and −0.59 for DD + RET + N) and fertiliser N application rate (r = 0.43 for CC + BURN + N and 0.31 for DD + RET + N). Based on the 37-year historic simulations, multivariate regression models for estimating annual N2O emissions were developed to account for climatic variation, and explained about 50% of variations of annual N2O emissions estimated by WNMM.