A model and its implications for denitrification in soil environment

We analyzed the mechanisms of a soil nitrogen (N) sub-model, which is a subroutine of the Crop-Environment Resources Synthesis (CERES)-maize; a model which was originally designed to simulate crop yield and has been calibrated and validated in Taiwan. Some experiments designed specifically for testing the N sub-model proved the capability of the model in reflecting field observations. With the mechanisms, we could write computer programs for calculating the relative sensitivities of major parameters in the model, and for simulating different treatments of organic matter. The purposes were to find how they affected N transformations, especially the processes of denitrification, which are considered to be responsible for N losses in upland soils and are an important environmental issue related to human disturbance of the N cycle. The results implied that soil water content and temperature were, respectively, the first and second dominant factors. They were much more sensitive than any other parameters, such as the decomposition rate coefficients, soil pH and bulk density. Decomposition of organic matter could slow down if organic matter with different carbon/nitrogen (C/N) ratios were treated in fractions. This treatment could also decrease the process of denitrification unless the organic matter was extremely large in quantity and has a high C/N ratio.