SWAT-N2O coupler: An integration tool for soil N2O emission modeling

Nitrous oxide (N2O) is one of the types of diffuse gaseous nitrogen lost mainly from agricultural soil, and it is a potent greenhouse gas contributing to climate warming. Both empirically based and process-based (e.g., Soil and Water Assessment Tool, SWAT) modeling methods for simulating N2O emissions have been used, and each has its own advantages and disadvantages. We first developed an empirically based N2O emission algorithm using 4488 individual measurements. By integrating the modified hydrological model for paddy fields, empirical N2O models for non-paddy fields and paddy fields into SWAT's existing crop growth, hydrology, and nitrogen cycling algorithms, we then created new modeling tools (SWAT-N2O coupler tools) that allow users to perform simulations of soil N2O emissions for non-paddy fields and paddy fields at different temporal-spatial scales. Furthermore, our tools allow users to efficiently conduct a time-space analysis by using the spatio-temporal analysis module and the sensitivity analysis by using scenario analysis module. The developed tools were demonstrated in an agricultural watershed in northeast China. The model performance and temporal-spatial evaluation indicate that the SWAT-N2O coupler tools would be an alternative and a useful way to capture the magnitudes and seasonal pattern of N2O fluxes in non-paddy fields and paddy fields. A further sensitivity analysis indicates that N2O emissions are sensitive to precipitation and applied N rate in paddy fields, moderately sensitive to precipitation in non-paddy fields as well as to air temperature in paddy fields, and relatively insensitive to the applied N rate and air temperature in non-paddy fields. The developed coupler tools could reliably depict how these factors interact and their effect on N2O emissions or absorptions under different cropping systems.