Comparing the inverse parameter estimation approach with pedo-transfer function method for estimating soil hydraulic conductivity

The soil hydraulic conductivity was evaluated by the inverse parameter estimation method using the cumulative infiltration data measured by the tension infiltrometer. The inverse parameter estimation approach combines the Levenberg-Marquardt nonlinear optimization method with the variably saturated flow equation. In addition to the inverse parameter estimation method, soil hydraulic conductivity was also determined by various pedotransfer functions (PTF) which can be used to estimate soil hydraulic conductivity indirectly. The soil texture contents and organic carbon content were measured at experimental sites and used as input variables for PTF. A measure of root mean square error (RMSE) and mean absolute error (MAE) was utilized to compare soil hydraulic conductivity values between numerical inverse solution and PTF. The comparison of various PTFs indicated that PTF of Wösten et al. (1999) combined with the PTF of Cosby et al. (1984) was the best predictor for saturated hydraulic conductivity compared to the inverse solution. For unsaturated hydraulic conductivity, the PTF of Schaap (1999, SSC) showed the best prediction. The accuracy of various PTFs is highly variable depending on the saturated water content information. The results and method presented in the paper can be used as a hypothesis for further investigation and formulation of PTF applicable to soil condition in Korea.