Inverse Estimation and Validation of Hydraulic Parameters of Paddy Soils under Humid Conditions Based on HYDRUS-1D Simulation

In humid regions, the infiltration-percolation characteristics and water retention capacity of paddy soils are key factors that determine the efficiency of irrigation water use and the accuracy of groundwater recharge simulation. This study selected three typical paddy soil profiles (0-60 cm) in the Songnen Plain as the research objects. The soil water retention curves and saturated hydraulic conductivity were accurately measured using the pressure plate apparatus and constant-head infiltration tests (Ks ranged from 1.9×10⁻⁵ to 5.4×10⁻⁶ m/s). The Van Genuchten model parameters were estimated using the Rosetta pedotransfer function based on artificial intelligence algorithms. A one-dimensional unsaturated flow model was established using HYDRUS-1D based on the measured parameters to simulate soil water dynamics during three irrigation events and one heavy rainfall event (42.7 mm). Model validation showed that the simulated values had good agreement with measured data, with a coefficient of determination (R²) of 0.91 and a Nash-Sutcliffe efficiency (NSE) of 0.88. This indicates that the inversely estimated parameters were applicable. The study found that clayey paddy soils exhibited a clear surface ponding effect and slow deep percolation under high water content conditions. This hydraulic heterogeneity provides important guidance for optimizing regional irrigation practices and managing groundwater resources.