A process-based model of N2O emission from a rice-winter wheat rotation agroecosystem: structure, validation and sensitivity

In this study, in order to numerically simulate daily nitrous oxide (N2O) emission from a rice-winter wheat rotation cropping system, we developed a process-based site model (referred to as IAP-N-GAS) tracking the movement and transformation of several forms of nitrogen in the agroecosystem, which is affected by climate, soil, crop growth and management practices. The simulation of daily N2O fluxes, along with key daily environmental variables, was validated with three-year observations conducted in East China. The validation demonstrated that the model simulated daily solar radiation, soil temperature and moisture well, and it almost exactly captured the dynamics and magnitude of accumulated rice above-ground biomass and mineral nitrogen in the soil. The simulated daily N2O emissions over all three years investigated were generally in good agreement with field observations. In particular, the peak N2O emissions induced by fertilizations, rainfall events or mid-season drainages, were well simulated. The model simulation also closely represented the inter-annual variation in N2O emission. These validations imply that the model has the capability to capture the general characteristics of N2O emission from a typical rice-wheat rotation agroecosystem. Sensitivity analyses revealed that the simulated N2O emission is most sensitive to the fertilizer application rate and the soil organic matter content, but it is much less sensitive to variations in the soil pH and texture, temperature, precipitation and crop residue incorporation rate under local conditions.