Field scale N 2 O flux measurements from grassland using eddy covariance

In order to assess nitrous oxide (N 2 O) 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 N 2 O at field scale (103–104 m 2 ), which are valuable for extrapolation to regional scales. In this paper three of the four fertilizer applications were investigated in detail. N 2 O 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 N 2 O-Nm -2 s -1 . Daily fluxes were averaging about 300 ng N 2 Om -2 s -1 over the 4 days following fertilizer application. The response of N 2 O emissions was less evident after the August fertilization, although 2 days after fertilizer application an hourly maximum flux of 554 ng N 2 O-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 N 2 O emission was not observed after fertilizer application in March 2003, due to lack of rainfall. The total N 2 O flux from June 2002 to June 2003 was 5.5 kg N 2 O-N ha -1 y -1 , which is 2.8% of the total annual N fertilizer input.