Modelling nitrous oxide abatement strategies in intensive pasture systems

Nitrous oxide emissions from grazed pasture soils are both spatially and temporally highly variable, making accurate measurement of emissions difficult and expensive. Simulation modelling is powerful tool in evaluating best management practices for N management in a systems context. The objective of this study was to use a biophysical, mechanistic model (DairyMod) to evaluate the potential impact of a range of N management practices on both pasture growth and N2O loss from an intensively grazed dairy pasture. The study suggests that N2O emissions can be substantially reduced by only applying N fertiliser when plants are N-limited, and by applying N fertiliser at rates below 50 kg N/ha per application. The predicted production loss from these strategies, relative to N applied after each grazing, was only 4% or less, assuming additional forage was not required during peak growth periods. The study also suggests that N2O emissions may be lower from urea–N fertiliser, when applied to pastures during the cooler and wetter months, than from using a pure nitrate–N source. The relative differences between the management interventions evaluated provide valuable information in assessing the potential N2O abatement and production impacts of proposed best management practices.