Managed grasslands: A greenhouse gas sink or source?

We describe a unique, one year investigation of CO₂ and N ₂O fluxes over a fertilized grassland in Ireland using two eddy covariance systems. As the global warming potential (GWP) of N ₂0 is 296 (100 year time horizon), relatively small N ₂0 emissions have a potentially large impact on overall radiative forcing. Therefore nitrogen fertilizer application practices may possibly turn a site with a net CO₂ uptake into a net radiative forcing source. We observed a net annual uptake of 9.45 T CO ₂ ha^-1. N₂O emissions equivalent to 5.42 T ha^-1 CO₂ GWP counteracted 57% of the effect of the CO₂ uptake, Estimated methane emissions from ruminants (3.74 T ha^-1 CO₂ GWP) further counteract the CO₂ uptake, making the overall GWP nearly neutral. This delicate balance of the greenhouse gas fluxes underscores the significance of fertilizer application strategies in determining whether a managed grassland is a net GWP source or sink.