Estimation of Field Capacity and Permanent Wilting Point of Plant Using Double-Rings Data and Inverse Numerical Solution in Different Soil Textures

In this study, HYDRUS-2D/3D software was used to estimate the field capacity (FC) and permanent wilting point (PWP) using double-rings infiltration data via inverse solution. For this purpose, the double rings infiltration data obtained from 95 points of different regions in Isfahan were used as model input. The studied soils were classified into seven textural classes including Sandy Loam (SL), Clay (C), Loam (L), Silty Loam (SiL), Clay Loam (CL), Silty Clay Loam (SiCL), and Silty Clay (SiC). For most soil samples, the simulated values ​​of FC and PWP were less than the measured values. The results showed that the lowest error value in estimating FC was related to SL texture (R2 = 0.884 and RMSE = 0.021) and the highest error value for FC estimation was related to Clay texture (R2 = 0.1 and RMSE = 0.122). Furthermore, the lowest and the highest error values for PWP estimation were observed in Loam (R2 = 0.858 and RMSE = 0.003) and Clay (R2 = 0.21 and RMSE = 0.025) soils, respectively. In general, the simulation error increased with increasing clay content in the soil. The estimated PWP values ​​were relatively more consistent than the estimated FC values with their measured values, in all soil samples. Coefficients of determination (R2) were 0.77 and 0.80 for FC and PWP in all soils, respectively. In general, the inverse numerical solution method had acceptable accuracy for estimating FC and PWP, especially in light textured soils.