Comparison between APSIM and NZ-DNDC models when describing N-dynamics under urine patches

Nitrous oxide (N2O) emissions from soil are the result of complex interactions between physical, chemical and biological processes. We compared two process-based models (APSIM and NZ-DNDC) with measurements of N2O emissions, soil NH4 and NO3 content (0–75 mm) and water-filled porespace from a series of field campaigns where known amounts of animal urine-N were applied to four soil types under permanent pastures, in two regions within New Zealand, at different times of the year. We also compared cumulative N2O emissions with an N2O inventory emission factor approach (EF3 method). Overall, the two process-based models performed less well than the EF3 method for simulating cumulative N2O emissions over the complete data set. However, in winter, the APSIM model correlated well with measurements (r = 0.97), while NZ-DNDC performed well on the Otago soils (r = 0.83 and 0.92 for Wingatui and Otokia, respectively). The process-based models have the potential to account for the effect of weather conditions and soil type on N2O emissions that are not accounted for by the EF3 method. However, further improvements are currently needed. The fractions of N lost to different processes within the complex soil–plant atmosphere system differed between the two models. The size of the predicted plant uptake, NO3 leaching and NH3 volatilisation fluxes are large compared with N2O emissions and could affect the simulated soil N pools and thus the predicted N2O fluxes. To simulate N2O fluxes accurately, it is therefore important to ensure these processes are well modelled and further validation studies are needed.