MEASUREMENT OF NITROUS-OXIDE EMISSION FROM AGRICULTURAL LAND USING MICROMETEOROLOGICAL METHODS

The spatial variability of N2O emission from soil makes extrapolation to the field scale very difficult using conventional chamber technique s (<1 m(2)). Micrometeorological techniques, which integrate N2O fluxe s over areas of 0.1 to 1 km(2) were therefore developed and compared w ith chamber methods over arable cropland. Measurements of N2O emission from an unfertilised organic soil (reclaimed from the sea in 1879) we re made over a 10 d period at Lammefjord, Denmark. Flux-gradient and c onditional sampling techniques were applied using two tunable diode la ser spectrometers (TDLs), a Fourier transform infra-red spectrometer ( FTIR) and a gas chromatograph (GC). Eddy covariance measurements were also made by the TDLs. Over the 10 d campaign approximately 5 d of con tinuous fluxes by the different methods were obtained. Fluxes determin ed by eddy covariance were in reasonable agreement, showing a mean flu x of 269 mu g N m(2) h(-1). Flux-gradient techniques measured a mean f lux of 226 mu g N m(-2) h(-1). The mean flux measured by conditional s ampling was 379 mu g N m(-2) h(-1). The maximum annual emission of N2O from this soil system was estimated to be 23.5 kg N ha(-1).