Effect of the nitrification inhibitor (DMPP) on soil nitrous oxide emissions and yield in a lettuce crop in Queensland, Australia

The use of nitrification inhibitors, in combination with ammonium based fertilisers, has been promoted recently as an effective method to reduce nitrous oxide (N2O) emissions from fertilised agricultural fields, whilst increasing yield and nitrogen use efficiency. However, to date no data is available on the use of nitrification inhibitors in sub-tropical vegetable systems. A field experiment investigated the effect of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N2O emissions and yield from lettuce production in sub-tropical Australia. Soil N2O fluxes were monitored continuously over 120 days with a fully automated system. Measurements were taken from three subplots for each treatment within a randomized complete blocks design. Cumulative N2O emissions over the 120 day observation period amounted to 191, 93 and 46 g-N ha-1 in the conventional fertiliser (CONV), the DMPP treatment and the zero fertiliser (0N) respectively. Consequently, the use of DMPP decreased seasonal N2O emissions by more than 50%, but had no significant impact on lettuce yield. The temporal variation of N2O fluxes showed only low emissions over the lettuce cropping period in all treatments, but significantly elevated emissions were observed in the CONV fertilized and DMPP treatment postharvest, following lettuce residues being incorporated into the soil. This study highlights that DMPP can substantially reduce N2O emissions from vegetable cropping systems. It also emphasizes that N input from vegetable crop residues incorporated into the soil after harvest can lead to substantially elevated N2O emission. Hence, in such systems post-harvest emissions need to be in the centre of attention for developing N2O mitigation strategies