A modeling approach of the relationship between nitrous oxide fluxes from soils and the water-filled pore space

Nitrous oxide (N2O) fluxes can increase significantly following small increases in soil water-filled pore space (WFPS). Thus, it is essential to improve our knowledge of this crucial relationship to better model N2O emissions by soils. We studied how much the addition of a gas transport and a gas-liquid equilibrium module to the model of N2O emissions NOE could improve simulation results. A sensitivity analysis of the modified model (NOEGTE: gas transport and equilibrium) was first performed, and then the model was tested with published data of a wetting-drying experiment. Simulated N2O fluxes plotted against WFPS appeared to be bell-shaped during the 7 days simulated, combining the effects of the low N2O production for WFPS < 0.62, and the slow gas diffusion for WFPS > 0.95. The WFPS generating the maximum simulated N2O fluxes shifted with time, from 0.76 after 12 h, to 0.79 after 168 h, because of an increase over time of the gas concentration gradient between the soil surface and the atmosphere. NOEGTE appeared able to capture the pattern of N2O emissions monitored in the experimental data. In particular, N2O peaks during drying were well reproduced in terms of timing, but their magnitudes were often overestimated. They were attributed to the increasing gas diffusivity and N2O exchanges from the liquid phase to the gaseous phase.