Comparison of three modeling approaches for simulating denitrification and nitrous oxide emissions from loam-textured arable soils

[1] Soil denitrification fluxes and nitrous oxide (N2O) emissions from the soil surface simulated by a Water and Nitrogen Management Model (WNMM), with three different gas modules, are compared to measurement data sets from two irrigated wheat-maize systems at two locations in the North China Plain (NCP) ( 2 years of measurement at the Luancheng site and 1 year of measurement at the Fengqiu site). The three gas modules are the WNMM gas module, the DAYCENT gas module, and the DNDC gas module. The term gas module used in this paper refers to the model component which simulates N2O emission from the processes of soil nitrification and denitrification. Soil water, temperature, organic matter decomposition, other nitrogen (N) transformations, such as mineralization and immobilization, and crop growth are simulated by the WNMM platform. For the 2-year data set from Luancheng, the three gas modules generate similar soil mineral N dynamics in the 0 - 20 cm topsoil. The daily time step, simply structured WNMM gas module consistently performs the best among the three gas modules for predicting soil denitrification fluxes (R-2 = 0.28, n = 39, p = 0.0006) and N2O emissions (R-2 = 0.45, n = 36, p < 0.0001). Up to 73, 43, and 22% of total N2O emissions are nitrification-induced as simulated by the DNDC, DAYCENT, and WNMM gas modules respectively, in this well-drained loam soil during the 2-year simulation. When applied to the 1-year data set at the Fengqiu site, the WNMM gas module consistently performs better in estimating N2O emissions (R-2 = 0.54, n = 35, p < 0.0001) compared to the other two modules. Simulations using the DNDC and DAYCENT gas modules explain over 40% of the temporal variation of N2O emission from the soil. Further testing on different soils and different agroecosystems is needed to confirm the superior performance of the WNMM gas module observed in this simulation study.