Terry J Rose1, Lee J Kearney1, Stephen Kimber2, Stephen Morris2, Peter Quin1, Lukas van Zwieten1,2
1 Southern Cross University, Military Road, East Lismore, NSW, 2480, www.scu.edu.au
2 NSW Department of Primary Industries, 1243 Bruxner HWY, Wollongbar, NSW, 2480, www.dpi.nsw.gov.au
While there is a growing body of literature suggesting that the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) can reduce N2O emissions from soils in temperate environments, there is little evidence of its efficacy in subtropical and tropical environments where temperatures and rainfall intensities are typically higher. We investigated N2O emissions in aerobic rice crops in a subtropical environment in late summer/autumn in 2014 and in an adjacent field in late summer/autumn in 2015. Crops received 80 kg/ha N as either urea, DMPP-urea, or a blend of 50 % urea and 50 % urea-DMPP in 2014, and urea, urea-DMPP or polymer-coated urea (PCU) in 2015. DMPP-urea significantly (P < 0.05) lowered soil N2O emissions in the 2013-14 season during the peak flux period after N fertiliser was applied, but had no effect in the 2014-15 season. The mean cumulative N2O emissions over the entire growing period were 190 g N2O-N/ha in 2013-14 and 413 g N2O-N/ha in 2014-15, with no significant effect of DMPP or PCU. Our results demonstrate that DMPP can lower N2O emissions in subtropical, aerobic rice crops during peak flux events following N fertiliser application in some seasons, but inherent variability in soil N2O emissions limit the chances of detecting significant differences in cumulative N2O flux over longer time periods. A greater understanding of how seasonal and/or soil factors impact the efficacy of DMPP in lowering N2O emissions following N fertiliser application in the subtropics is needed to formulate appropriate guidelines for its use commercially.