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

Abstract

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.