*2.2. Numerical Model*

HYDRUS-1D is widely used in saturated-unsaturated zones of water, heat and solute transport to study the process of nitrogen migration and the transformation in the fluctuation zone at the groundwater level. In this paper, based on indoor physical experiments, a numerical model of nitrogen migration and change in the Vadose zone–saturated zone coupled with water transport and solute transport, was constructed using HYDRUS-1D.
