Comparison of Simultaneous Soil Profile N2O Concentration and Surface N2O Flux Measurements Overwinter and at Spring Thaw in an Agricultural Soil

A field experiment was carried out in Ontario, Canada to compare independently measured soil N2O profile concentration and surface N2O flux measurements overwinter and at spring thaw, to estimate the soil N2O content accumulation overwinter, and to estimate the magnitude of the contribution of the physical release of trapped N2O to surface fluxes at spring thaw. Gas samples at various depths were taken and N2O concentrations determined, soil profile gaseous N2O content was calculated by estimating the air-filled pore-space from soil condition measurements, and soil aqueous N2O content was calculated using liquid water content measurements and applying Henry’s Law. Soil N2O content was found to reach a maximum of ~25 mg N2O m-2, and by comparing changes in soil N2O content to surface fluxes measured using the micrometeorological flux-gradient technique, the physical release of previously produced N2O was estimated to contribute up to 47% of spring thaw N2O surface fluxes.