Quantifying annual N2O emission fluxes from grazed grassland under a range of inorganic fertiliser nitrogen inputs

The objective of the present study was to measure emissions of N2O from fertilized grazed grassland that can be used to add valuable information to the limited existing data on N2O fluxes from grazed grassland and aid the development of new country-specific EFs for direct emissions from soils in the UK. This was done by evaluating the effect on N2O emissions of inorganic fertiliser N applied to grazed grassland soils over the range of N inputs 0–350 kg ha−1. Nitrous oxide fluxes were measured using closed static chambers at 3 sites in England and Wales over a two-year period. Cumulative fluxes were calculated and the total emission regressed against applied inorganic fertiliser N in order to estimate the emission factor for N2O emissions from soils. The data showed that, the emission factor for N2O from inorganic fertiliser applied to grazed grassland soils in the UK differs from the IPCC default value of 1.25%. A nonlinear response of N2O emissions to fertiliser N application rates was observed. Annual emissions of N2O were estimated from a modelled function fitted to the measured data and after subtraction of the background flux resulted in emissions of 0.5 and 3.9 kg N2O–N ha−1 yr−1 for an application of 100 kg N for three locations in the UK, one in the East and the other two in the West of the UK (after combining the data from two sites), respectively.