Strategies for mitigating N 2 O and N 2 emissions from an intensive sugarcane cropping system

In sugarcane cropping systems, high rates of N fertiliser are typically applied as sub-surface bands creating localised zones of high mineral N concentrations. This in combination with high levels of crop residue (trash) retention and a warm and humid climate creates conditions that are known to promote soil denitrification, resulting in high emissions of the potent greenhouse gas N 2 O. These losses illustrate inefficient use of N fertilisers but total denitrification losses in the form of N 2 and N 2 O remain largely unknown. We used the 15 N gas flux method to investigate the effect of cane trash removal and the use of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N 2 and N 2 O emissions on a commercial sugarcane farm at Bundaberg, Australia. High gaseous N losses were observed under the standard grower practice where cane trash retention and N fertiliser application (145 kg N ha −1 as urea) resulted in N 2 and N 2 O emissions (36.1 kg N ha −1 ) from the subsurface N fertiliser band, with more than 50% of these losses emitted as N 2 O. Cane trash removal reduced N 2 emission by 34% and N 2 O emission by 51%, but had no effect on the N 2 O/(N 2 + N 2 O) ratio. The use of DMPP lowered N 2 and N 2 O emission by 35% and 98%, respectively, reducing the percentage of these losses (N 2 + N 2 O) emitted as N 2 O to only 4%. We conclude that the use of DMPP is an effective strategy to reduce N losses, minimise N 2 O emissions, while keeping the benefits of cane trash retention in sugarcane cropping systems.