Effect of residue management and nitrification inhibitor on N2O and N2 emissions from an intensive sugarcane cropping system in sub-tropical Australia

Sugarcane is typically produced under conditions that are known to stimulate soil denitrification, i.e. high fertiliser inputs in combination with high levels of crop residue (trash) retention and a warm and humid climate, and high levels of fertiliser N losses from intensive sugarcane systems have been reported. However, there is still insufficient reliable data on N₂ losses from sugarcane soils based on field measurements since it is inherently challenging to measure N₂ emissions against the high atmospheric N₂ background. This study investigated the effect of cane trash removal and the use of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N₂ and N₂O emissions on a commercial sugarcane farm in sub-tropical Australia using the ¹⁵N gas flux method. Substantial gaseous N losses were observed under current management practice where cane trash retention and N fertiliser application (145 kg N ha^-1 as urea) resulted in elevated losses of N₂O and N₂ from a subsurface N fertiliser band, with more than 50% of these gaseous N losses emitted as N₂O. Cane trash retention increased the magnitude of N₂O and N₂ emissions reflecting overlapping effects of increased soil water content and labile C supply from residues, but had no effect on the N₂O/(N₂+N₂O) ratio. The NI DMPP was extremely effective in reducing overall N₂O and N₂ losses and also promoted complete denitrification of N₂O to environmentally benign N₂, with only 4% of total N₂O and N₂ losses emitted as N₂O. This shows that DMPP might be especially effective in reducing N₂O emissions from banded fertiliser were localized zones of high NO₃^- concentration around the fertiliser band are created that are particularly vulnerable to denitrification. Consequently, the use of DMPP in sugarcane systems with banded fertiliser does not only offer environmental benefits by reducing N₂O emissions but also substantially reduces overall denitrification losses, providing an effective strategy to improve NUE and reduce N₂O emissions for the Australian sugarcane industry.