Measurement of nitrous oxide emission from agricultural land using micrometeorological methods

Abstract

The spatial variability of N2O emission from soil makes extrapolation to the field scale very difficult using; conventional chamber techniques ( < 1 m2). Micrometeorological techniques, which integrate N2O fluxes over areas of 0.1 to 1 km2 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 μg N m2 h−1. Flux-gradient techniques measured a mean flux of 226 μg N m−2 h−1. The mean flux measured by conditional sampling was 379 μg 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.