Simulation and Evaluation of Soil Moisture Distribution Pattern under Pitcher underground Irrigation System

Due to the limited water resources in arid regions، using modern irrigation methods with high efficiency in agriculture is essential. One of the methods for increasing water use efficiency is the pitcher underground irrigation method. A proper design of these systems requires the enough information about water flow distribution pattern in both horizontal and vertical directions. Since the field experiments for detecting soil moisture distribution pattern is very hard and time consuming، analytical methods can be used to reasonably estimate the distribution of moisture in the soil though soil water flow equations having soil water factors. The aim of this study was to investigate the moisture distribution pattern in soil using three different heights of irrigation water source (i. e. 1، 1. 5 and 2 meters) in the certain time intervals. This study was done in a randomized complete blocks design with three replications. Volumetric soil moisture content within 1m-soil profile was measured by TDR. Simulation of water movement in soil was performed by HYDRUS-2D and the simulated values were compared with the measured values at the end. The results show that the model can simulate moisture variation trend with a relatively good accuracy. In the early stage of irrigation، simulator overestimated the moisture content. Moisture variation was not too much at distance 30 cm from vertical axis of the pitcher. This was confirmed by HYDRUS-2D simulated values. The best simulation results were obtained for the 10 cm distance from the vertical axis of pitcher where ME، RMSE and R2 were 0. 0015، 0. 018 and 0. 95، respectively. Moreover it was observed that there is no significant difference between soil water distribution pattern obtained for two water supply elevations of 1. 5 and 2 m above the soil surface. The results indicated that HYDRUS-2D can effectively use to simulate soil water distribution pattern under a porous clay pitcher irrigation system.