The effect of future climate perturbations on N₂O emissions from a fertilized humid grassland

N₂O emissions from a fertilized humid grassland near Cork, Ireland were continuously measured during 2003 using an eddy covariance system. For most of the year emissions were close to zero and 60% of the emissions occurred in eight major events of 2-20 days' duration. Two hundred and seven kg ha^-1 of synthetic N and 130 kg ha^-1 organic N were applied over the year and the total measured annual N₂O emission was 11.6 kg N ha^-1. The flux data were used to test the prediction of N ₂O emissions by the DNDC (DeNitrification - DeComposition) model. The model predicted total emissions of 15.4 kg N ha^-1, 32 % more than the observed emissions. On this basis the model was further used to simulate (a) background (non-anthropogenic) N₂O emissions and (b) the effect on N₂O emissions of future climate perturbations based on the Hadley Center model output of the IS92a scenario for Ireland. DNDC predicts 1.7 kg N ha^-1 year^-1 of background N₂O emissions, accounting for 15% of the observed emissions. Climate shifts will increase total annual modeled N₂O emissions from 15.4 kg N ha^-1 to 22.4 kg N ha^-1 if current levels of N applications are maintained, or to 21.2 kg N ha^-1 if synthetic N applications are reduced to 170 kg N ha^-1 to comply with recent EU water quality legislation. Thus the projected increase in N₂O emissions due to climate change is far larger than the decrease expected from reduced fertilizer applications.