ANALYTICAL MODELING OF NITROGEN DYNAMICS IN SOILS AND GROUND WATER

An analytical model, known as RISK-N, is developed to simulate nitrogen cycling in soils, and nitrate transport and fate in soils and ground water. The soil is separated into upper-root, lower-root, and intermediate-vadose zones, each with uniform properties. Transport in each soil zone is modeled on the basis of complete mixing. Transport in the aquifer, however, is modeled using a two-dimensional advection-dispersion transport equation. A simulation is made with a hypothetical corn plot, using meteorological, soil, hydrologic, and hydrogeological data for the South Platte River region of northeastern Colorado. Sensitivity analyses are performed on model parameters. This study shows that the RISK-N model is capable of simulating nitrate leaching rates, as well as ground-water concentrations, that are consistent with those obtained by numerical models, while requiring fewer input variables.