Nitrous Oxide Flux from Fertilised Grassland: Strategies for Reducing Emissions

Abstract

Nitrous oxide emissions from soils, through the processes of nitrification and denitrification, are increased by N fertiliser application. The effect of choosing a form of N fertiliser appropriate to the environmental conditions, and the effect of nitrification inhibitors, on N₂O emissions, were studied on a grassland site over two growing seasons. Total emissions were greatest from urea fertiliser, with the greatest losses coming from urea applications in the warmer, drier months of June and August, suggesting that the N₂O was formed mainly via nitrification. The greatest emissions of N₂O from ammonium nitrate fertiliser occurred after applications in April in relatively wet conditions, when the emissions from urea and ammonium sulphate were low, indicating that denitrification was probably responsible. The application of the nitrification inhibitor dicyandiamide (DCD) reduced emissions from the ammonium-based fertilisers by up to 64%. A single application of nitrapyrin reduced emissions by up to 52%. When urea fertiliser was applied in the spring, followed by ammonium nitrate later in the growing season, the emissions of N₂O were lower than when only urea or only ammonium nitrate were used throughout the season; the reduction was similar to that obtained using the nitrification inhibitors.