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.\ud However, to date no data is available on the use of nitrification inhibitors in sub-tropical vegetable systems.\ud 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.\ud Soil N₂O fluxes were monitored continuously over 120 days with a fully automated system.\ud Measurements were taken from three subplots for each treatment within a randomized complete blocks design.\ud 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.\ud Consequently, the use of DMPP decreased seasonal N₂O emissions by more than 50%, but had no significant impact on lettuce yield.\ud 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 post-harvest, following lettuce residues being incorporated into the soil.\ud This study highlights that DMPP can substantially reduce N₂O emissions from vegetable cropping systems.\ud It also emphasizes that N input from vegetable crop residues incorporated into the soil after harvest can lead to substantially elevated N₂O emission.\ud Hence, in such systems post-harvest emissions need to be in the centre of attention for developing N₂O mitigation strategies