Nitrogen dynamics in the soil under the condition of environmentally friendly fertilization practices (EFFPs) is described by a comprehensive N-dynamics model. The model (first paper of this series, Transport in Porous Media 31(3) (1998), 249-274) is different from other models in its capability of simulating the special phenomena related to the application of EFFPs. In this paper, a finite difference method is used to solve the mathematical model. The numerical model is verified by simulating several water flow and conservative solute transport problems with existing numerical or analytic solutions. The good agreements between our simulation results and the solutions given by others show that our model is reliable in simulating flow and transport problems in the soil. Preliminary model validation is conducted by applying the model to simulate two field experiments. The acceptable agreements between our numerical simulation results and experimental data demonstrate that the model can reasonably model N-dynamics in the soil under field conditions.