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 techniques (<1 m(2)). Micrometeorological techniques, which integrate N2O fluxes over areas of 0.1 to 1 km(2) were therefore developed and compared with chamber methods over arable cropland. Measurements of N2O emission from an unfertilised organic soil (reclaimed from the sea in 1879) were made over a 10 d period at Lammefjord, Denmark. Flux-gradient and conditional sampling techniques were applied using two tunable diode laser 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 continuous fluxes by the different methods were obtained. Fluxes determined by eddy covariance were in reasonable agreement, showing a mean flux of 269 mu g N m(2) h(-1). Flux-gradient techniques measured a mean flux of 226 mu g N m(-2) h(-1). The mean flux measured by conditional sampling 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).