Assessment of improved soil hydraulic parameters for soil water content simulation and irrigation scheduling

The efficient irrigation systems utilizing numerical models based on Richard's flow equation require key input parameters, soil hydraulic parameters (SHPs). The present study proposes a method to determine the SHPs from the soil water contents at field capacity and wilting point, which are determined for irrigation scheduling. It also compares them with the SHPs estimated by various pedotransfer functions (PTFs) to simulate respective soil water retention curves (SWRCs). High efficiencies of 70-80 % were obtained in simulating the SWRCs by the proposed method as compared to PTFs. In order to further assess the applicability of the SHPs as determined, the experiments were conducted under real field conditions for wheat crop in Roorkee, India, and SWRCs were experimentally determined. These different sets of SHPs, along with experimentally determined saturated permeability, were then used as input parameters in root water uptake model and the results of observed and simulated soil water contents were compared under three different irrigation treatments. It was found that the experimentally obtained SHPs and those obtained by the proposed method were able to simulate the soil water contents with efficiencies of 70-80 % at all the depths for all the three irrigation treatments, while the PTFs performed poorly.