Nitrous oxide emissions from urea fertiliser and effluent with and without inhibitors applied to pasture

There is currently a limited number of New Zealand studies quantifying nitrous oxide (N2O) emission factors (EF1, N2O emissions as a percentage of N applied) for farm dairy effluent (FDE) and urea fertiliser. Therefore, two experiments were conducted in four regions of New Zealand to determine EF1 for FDE and urea fertiliser applied to pastures with contrasting soils and climatic conditions. Experiment 1 included urease and nitrification inhibitors to determine their effect on EF1. Urea treatments included (i) standard urea; (ii) urea amended with the nitrification inhibitor dicyandiamide (DCD) at 0.02 kg DCD kg−1 nitrogen (N) and (iii) urea amended with the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) at 250 mg nBTPT kg−1 urea, while FDE was applied with or without DCD, at 10 kg DCD ha−1. Experiment 2 focused solely on FDE, which was applied to pastures that had either never received FDE or had a history of repeated application of FDE over several years. Urea fertiliser produced a large variation in EF1 values, ranging from 0.03% to 1.52%. Application of FDE resulted in EF1 ranging from 0.06% to 0.94% across both experiments. The urease and nitrification inhibitors had little or no effect on reducing EF1 from urea fertiliser and FDE application. The history of repeated applications of FDE to pasture also had no effect on EF1.