Using the ecosys mathematical model to simulate temporal variability of nitrous oxide emissions from a fertilized agricultural soil

Large temporal variability of N 2O emissions complicates calculation of emission factors (EFs) needed for N 2O inventories. To contribute towards improving these inventories, a process-based, 3-dimensional mathematical model, ecosys, was used to model N 2O emissions from a canola crop. The objective of this study was to test the hypothesis in ecosys that large temporal variability of N 2O is due to transition among alternative reduction reactions in nitrification/denitrification caused by small changes in soil water-filled pore space (WFPS) following a threshold response, which controls diffusivity ( D g ) and solubility of O 2. We simulated emissions at field scale, using a 20 × 20 matrix of 36 m × 36 m grid cells rendered in ArcGIS from a digital elevation model of the fertilized agricultural field. Modelled results were compared to measured N 2O fluxes using the flux-gradient technique from a micrometeorological tower equipped with a tunable diode laser, to assess temporal N 2O variability. Grid cell simulations were performed using original, earlier and later planting and fertilizer dates, to show the influence of changing precipitation and temperature on EFs. Fertilizer application (112 kg N ha −1), precipitation and temperature were the main factors responsible for N 2O emissions. Ecosys represented the temporal variation of N 2O emissions measured at the tower by modelling significant emissions at WFPS > 60% which reduced the oxygen diffusivity, causing a rising need for alternative electron acceptors, thus greater N 2O production via nitrification/denitrification. Small changes in WFPS above a threshold value caused comparatively large changes in N 2O flux not directly predictable from soil temperature and WFPS. In ecosys, little N 2O production occurred at WFPS