No abstract

HYDRUS‐1D has been extensively applied to the simulation of wettable soil infiltration, but very few studies have explored its applicability to the infiltration of water‐repellent soil (WRS) at different depths. To this end, HYDRUS‐1D was used to simulate water movement of layered soil with a surface repellent thickness of 10 cm. The parameters of the van Genuchten model were calibrated and validated using cumulative infiltration (CI), distance of the wetting front (Zf) and volumetric water content (θv) through five respective treatments. Another 10 tilled scenarios were selected to simulate water movement of tilled WRS. RRMSE (relative root mean square error) and CRM (coefficient of residual mass) were adopted to evaluate simulation accuracy. For the calibration and validation, the RRMSE values ranged from 0.04 to 0.251 and 0.042 to 0.101, respectively, indicating that HYDRUS‐1D could effectively simulate water movement of WRS. Furthermore, for layered treatments, the simulation accuracy of θv, CI and Zf decreased with the increase of the degree of repellency and thickness. The treatments with the repellent thickness of 10 cm had higher simulation accuracy than that with repellent thickness of 5 cm when the top layer had the same WRS. The results revealed HYDRUS‐1D was effective in the simulation of water movement in repellent clay loam with different degrees of repellency and depths. Highlights The applicability of HYDRUS‐1D to the infiltration of water‐repellent soil (WRS) at different depths was explored. The simulation of different degrees of repellency and depths was first conducted. Simulation accuracy decreased with the increase of degree of repellency and thickness. HYDRUS‐1D was effective in simulating water movement of repellent soil.

Water repellency has a great influence on water infiltration into soil. Currently, there is no modified correlation model that is applicable to the water infiltration of water-repellent soils (WRS). In order to better construct a model suitable for water infiltration in water-repellent soil, our objectives are to validate the effect of a modified Green-Ampt model. We modified the model by assuming that the saturated and unsaturated zones had the same thickness and by combining three formulas of the suction head (Sf VG, Sf BC, Sf GP) and the average saturated hydraulic conductivity. Therefore, we obtained three modified models: the Green-Ampt-VG, Green-Ampt-BC, and Green-Ampt-GP models. Indoor one-dimensional water infiltration experiments were conducted to simulate the cumulative infiltration (CI), the distance of the wetting front (Zf), and the infiltration rate of a hydrophilic treatment and repellent treatments. The results showed that as the degree of repellency increased, the soil suction head decreased, and the relationship between the value of the soil suction head and the degree of WRS was exponential. In addition, the simulated values of the modified CI formula highly fit the measured values of all treatments in the three models (RMSE: 1.696, 1.812, and 0.694). The modified Green-Ampt-VG model had the best simulation effect on the infiltration rate (RMSE: 0.036) and Zf (RMSE: 3.976). The results indicated that the suction head values obtained from the parameters of the VG model were closest to the actual values compared the other models. These results can provide a reference for the solution of problems involving the suction head and water infiltration into WRS in the future.