Investigating uptake of N₂O in agricultural soils using a high-precision dynamic chamber method

Uptake (or negative flux) of nitrous oxide (N₂O) in agricultural soilsis a controversial issue which has proved difficult to investigate in thepast due to constraints such as instrumental precision and methodological uncertainties. Using a recently developed high-precisionquantum cascade laser gas analyser combined with a closed dynamicchamber, a well-defined detection limit of 4 μg N₂O-N m⁻² h⁻¹ could be achieved for individual soil flux measurements. 1220 measurements of N₂O flux were made from a variety of UK soils usingthis method, of which 115 indicated uptake by the soil (i.e. a negative fluxin the micrometeorological sign convention). Only four of these apparentlynegative fluxes were greater than the detection limit of the method, whichsuggests that the vast majority of reported negative fluxes from suchmeasurements are actually due to instrument noise. As such, we suggest thatthe bulk of negative N₂O fluxes reported for agricultural fields aremost likely due to limits in detection of a particular flux measurementmethodology and not a result of microbiological activity consumingatmospheric N₂O.