Prediction of soil hydraulic parameters by inverse method using genetic algorithm optimization under field conditions

In this study, soil hydraulic parameters were estimated by the inverse method in field conditions. At basins of 2 × 2 m, soil water content reached near saturation point up to about 1 m depth. Afterwards, the surfaces of the plots were covered by plastic sheets and the soil water content and pressure head were measured daily by TDR (time-domain reflectrometry) and ceramic tensiometers at different soil depths up to seven or 10 days later. The amounts of soil water content and pressure head were predicted in a profile by solving Richards' equation, applying the finite difference method. The values of soil hydraulic parameters [the parameters of soil water characteristic curve and matched saturated hydraulic conductivity (Ko)] were estimated by inverse method in which minimization of errors at different depths and times after wetting was obtained using genetic algorithm (GA). For prediction of soil hydraulic parameters, the ESHPIM2 model was developed based on the linkage of Richards' equation and GA method. The results showed that using the ESHPIM2 model was favorable. Because the effects of macropores in the movement of water under the inverse method were not taken into consideration, the predicted values of Ko were much lower than those measured by saturated hydraulic conductivity in field conditions.