Simulation of N2O emissions and mitigation options for rainfed wheat cropping on a Vertosol in the subtropics

The Water and Nitrogen Management Model (WNMM) was applied to simulate nitrous oxide (N2O) emissions from a wheat-cropped Vertosol under long-term management of no-till, crop residue retention, and nitrogen (N) fertiliser application in southern Queensland, Australia, from July 2006 to June 2009. For the simulation study, eight treatments of combinations of conventional tillage (CT) or no-till (NT), stubble burning (SB) or stubble retention (SR), and N fertiliser application at nil (0N) or 90 (90N) kg N/ha. year were used.The results indicated that WNMM satisfactorily simulated the soil water content of the topsoil, mineral N content of the entire soil profile (0-1.5 m), and N2O emissions from the soil under the eight treatments, compared with the corresponding field measurements. For simulating daily N2O emissions from soil, WNMM performed best for the treatment CT-SB-90N (R-2 = 0.48, P < 0.001; RMSE = 10.2 g N/ha. day) and worst for the treatment CT-SB-0N (R-2 = 0.03, P = 0.174; RMSE = 1.2 g N/ha. day). WNMM predicted N2O emissions from the soil more accurately for the fertilised treatments (i.e. 90N nu. 0N), and for the residue retained treatments (SR nu. SB). To reduce N2O emissions from the no-till and fertilised treatments, three scenarios were examined: application of nitrification inhibitor, application of controlled-release fertiliser, and deep placement of liquid fertiliser (UAN32). Only the deep placement of UAN32 below the 35 cm depth was effective, and could reduce the N2O emissions from the soil by almost 40%