The nitrification inhibitor DMPP applied to subtropical rice has an inconsistent effect on nitrous oxide emissions

Abstract

Although there is growing evidence that the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) can lower soil nitrous oxide (N2O) emissions in temperate environments, there is little evidence of its efficacy in subtropical or tropical environments where temperatures and rainfall intensities are typically higher. We investigated N2O emissions in field-grown aerobic rice in adjacent fields in the 2013-14 and 2014-15 seasons in a subtropical environment. Crops were topdressed with 80kg nitrogen (N) ha-1 before rainfall, as either urea, urea+DMPP (at 1.6kg DMPP t-1 urea: 'urea-DMPP') or a blend of 50% urea and 50% urea-DMPP in the 2013-14 season, and urea, urea-DMPP or polymer (3 month)-coated urea (PCU) in the 2014-15 season. DMPP-urea significantly (P<0.05) lowered soil N2O emissions in the 2013-14 season during the peak flux period after N fertiliser application, but had no effect in 2014-15. The mean cumulative N2O emissions over the entire growing period were 190g N2O-N ha-1 in 2013-14 and 413g N2O-N ha-1 in 2014-15, with no significant effect of DMPP or PCU. Our results demonstrate that DMPP can lower N2O emissions in subtropical, aerobic rice during peak flux events following N fertiliser application in some seasons, but inherent variability in climate and soil N2O emissions limited the ability to detect significant differences in cumulative N2O flux over the seasonal assessment. A greater understanding of how environmental and soil factors impact the efficacy of DMPP in the subtropics is needed to formulate appropriate guidelines for its use commercially.