Mechanistic model for nitrous oxide emission via nitrification and denitrification

Seasonal and annual N2O fluxes from urine-affected pasture were approximated with a mechanistic model based on Michaelis-Menten kinetics. The model combined the effects of soil nitrate-N, soil ammonium-N, soil temperature and soil moisture (all from the top 5 cm) to calculate N2O emissions from nitrification (F-nit) and denitrification (F-den), with total N2O emission being the sum Of the two (F-tot=F-nit+F-den), Best results were obtained when different kinetic parameters were used for periods of constant soil moisture conditions and after heavy rainfalls when a rapid change of the soil moisture status occurred. Modelled N2O emissions over a year were within the range of uncertainties of measured N2O emissions. Results indicate that the spatial variability of N2O emissions at times when all the model inupt variables were constant may be related to microorganism growth dynamics or enzyme production rates.