Simulation of Water Movement in Layered Water‐Repellent Soils using HYDRUS‐1D

Core Ideas HYDRUS‐1D performed well for the water movement in layered water repellent soils. Two scenarios of silt loam/sand and sand/silt loam with water repellent soils, were applied. HYDRUS‐1D simulated infiltration parameters by differing two layered water repellent scenarios. Water repellency has many negative influences on soil water movement. However, simulations of water movement in layered water repellent (WR) soils are limited. Our objectives are to calibrate and validate the infiltration parameters and simulate water movement in layered WR soils based on ponded infiltration experiments conducted in wettable, slightly WR, strongly WR, and severely WR soils. Our experiments were conducted in 50‐cm long soil columns with two layer scenarios: Silt loam overlying (/) sand and sand/silt loam. For WR treatments, the surface soil was all 5 cm. For the wettable treatments, surface soils with thicknesses of 10‐ and 20‐cm layer sequences were added. Calibrations were conducted based on cumulative infiltration (CI), distance of the wetting front ( Z f ), and volumetric soil water content (θ v ) in the wettable and WR silt loam/sand treatments. Validations were conducted via eight additional treatments. The 12 WR layered soil treatments were selected for simulation. Three statistical parameters including the relative root mean square error (RRMSE), were used to assess the HYDRUS‐1D performance. The RRMSE for calibration and validation, ranged from 3.2 to 10% and 2.5 to 13.6%, respectively, confirming that HYDRUS‐1D was able to accurately describe water movement in layered WR soils. For the severely WR treatments, infiltration time reached 2800 h in silt loam/sand scenario and 1000 h in sand/silt loam scenario when water infiltrated to a depth of 35 cm. Overall, soil water repellency was more important than the interlayer position in regard to affecting water movement in layered soils, especially in the sand/silt loam scenario.