Nitrous oxide emissions from animal urine as affected by season and a nitrification inhibitor dicyandiamide

Abstract

Nitrous oxide emissions from pasture soils account for one third of total agricultural greenhouse gas emissions in New Zealand. The aim of this study was to determine nitrous oxide (N2O) emissions from animal urine patches under summer (with irrigation) and winter conditions as affected by dicyandiamide (DCD) in grazed grassland in New Zealand. Sixteen monolith lysimeters were collected from an established perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) pasture on a Templeton fine sandy loam (Udic Ustochrept) located near Lincoln University on the Canterbury plains of New Zealand to study the N2O emissions from animal urine as affected by season and a nitrification inhibitor dicyandiamide. The experiment was conducted in the summer of 2008–2009 and the winter of 2009 with four treatments (control, control + DCD (10 kg ha−1), urine (1,000 kg N ha−1), urine + DCD) for both seasons. N2O fluxes from the pasture were measured in summer and winter. Results showed that the application of urine significantly increased N2O emissions and the application of nitrification inhibitor, DCD, to pasture soil was very effective in reducing N2O emissions both in summer and winter. Total N emissions from urine-N applied at 1,000 kg N ha−1 were 7.8 kg N2O–N ha−1 in the summer season and this was much lower than the 12.7 kg N2O–N ha−1 emitted during the winter season. The application of DCD reduced summer N2O–N emissions to 4.8 kg N2O–N ha−1 and winter N2O–N emissions to 3.9 kg N2O–N ha−1, representing 40% and 69% reductions in the summer and winter seasons, respectively. The results demonstrate that N2O emissions from animal urine-N in grazed pastures were much higher in the winter season than in the summer season with irrigation and that DCD was more effective in reducing N2O emissions in the high-emitting winter season.