Influence of Different Nitrogen Rates and DMPP Nitrification Inhibitor On Annual Nitrous Oxide Emissions From a Subtropical Wheat-Maize Cropping System.

Global cereal production will need to increase by 50 to 70 % to feed a world population of about 9 billion by 2050. This intensification is forecast to occur mostly in subtropical regions, where warm and humid conditions promote high N₂O losses from cropped soils. To secure high crop production without exacerbating N₂O emissions, new N fertilizer management strategies are needed. In our study we evaluated the efficacy of a nitrification inhibitor (3,4-dimethylpyrazole phosphate - DMPP) and different fertilizer N rates to reduce N₂O emissions in a wheat-maize rotation in subtropical Australia. Using a fully automated greenhouse gas measuring system, we monitored N₂O emissions from treatments fertilized with different rates of urea, including a control (40 kg-N ha^-1 annum^-1), a reduced N fertilizer rate (120 N), a conventional N fertilizer rate (240 N) and the conventional rate (240 N) with nitrification inhibitor (DMPP). Due to the high soil temperature and elevated N rates applied, the maize season was by far the main contributor to annual N₂O emissions. Annual N₂O emissions in the four treatments amounted to 0.49, 0.84, 2.02 and 0.74 kg N₂O-N ha^-1 year^-1 respectively, and corresponded to emission factors of 0.34, 0.40, 0.69 and 0.16% of total N applied. The application of DMPP produced a significant reduction in N₂O emissions only in the maize season. The use of DMPP with urea at the conventional N rate reduced annual N₂O emissions by more than 60% but did not affect crop yields. For both crops, the reduced N fertilizer rate led to N₂O emissions comparable to the DMPP treatment but severely penalized crop yields and soil fertility. Our study suggests that the application of DMPP is a feasible strategy to reduce annual N₂O emissions from sub-tropical wheat-maize rotations, in particular in the summer maize crop, where elevated N₂O fluxes can be expected.