Estimation of Soil Hydraulic Parameters with Measurment of Soil Water Content, Pressure Head or Measurment the Simultaneously by Inverse Method

Most processes of soil and water in the field occur in unsaturated conditions.In the field, It’s possible to estimate soil hydraulic properties by measurement of soil water content and soil water pressure head in different times, using inverse method. In the other hand, it’s difficult, time consuming and costly to measuring soil water content and water pressure head simultaneously. So, in this paper, the possibility of predicting soil hydraulic properties by measurement of soil water content or water pressure head separately were studied. To do this job, ESHPIM2, an inversion approach computer model, has been used. In this model, soil hydraulic parameters are optimized to reach the minimum value of objective function (Summation of squared differences between measured and predicted soil water content or water pressure head) using genetic algorithm. Soil hydraulic parameters of four soil series at Agricultural College of Shiraz University were studied in three cases. In the first case, the ESHPIM2 model with the objective function based on measuring the soil water pressure head and in the second case, the ESHPIM2 model with the objective function based on measuring the soil water content are used. Moreover, in the third case, soil hydraulic parameters are estimated by measuring soil water content and soil water pressure simultaneously. The results show that soil hydraulic parameters are predicted more appropriately by measuring soil water pressure head than soil water content in studied soils by inverse method using ESHPIM2 model.