Field Scale N2O Flux Measurements from Grassland Using Eddy Covariance

In order to assess nitrous oxide (N2O) emissions from typical intensively managed grassland in northern Britain fluxes were measured by eddy covariance using tuneable diode laser absorption spectroscopy from June 2002 to June 2003 for a total period of 4000 h. With micrometeorological techniques it is possible to obtain a very detailed picture of the fluxes of N2O at field scale (103–104 m2), which are valuable for extrapolation to regional scales. In this paper three of the four fertilizer applications were investigated in detail. N2O emissions did not always show a clear response. Hourly fluxes were very large immediately after the June 2002 nitrogen fertilizer application, peaking at 2.5 mg N2O–N m-2 s-1. Daily fluxes were averaging about 300 ng N2O m-2 s-1 over the 4 days following fertilizer application. The response of N2O emissions was less evident after the August fertilization, although 2 days after fertilizer application an hourly maximum flux of 554 ng N2O–N m-2 s-1 was registered. For the rest of August the flux was undetectable. The differences between fertilization events can be explained by different environmental conditions, such as soil temperature and rainfall. A fertiliser-induced N2O emission was not observed after fertilizer application in March 2003, due to lack of rainfall. The total N2O flux from June 2002 to June 2003 was 5.5 kg N2O–N ha-1y-1, which is 2.8% of the total annual N fertilizer input