Application of Hydrus-2D Model to Investigate the Soil Moisture Changes under Different Irrigation regimes of pistachio trees in Subsurface Drip Irrigation

Subsurface drip irrigation is the most suitable irrigation method to provide the water requirements for plants in the root environment. The management of this irrigation method is based on the science of water distribution in wet soil volumes. Simulation models can be used in obtaining this valuable knowledge. In this study, was evaluated simulation the distribution of soil moisture in the plant root zone under subsurface drip irrigation using the HYDRUS-2D model and based on a field research in a pistachio garden, in Sorkhe, Safaeieh, Semnan province, during two years of cultivation 2012-2013. The treatments were three irrigation regimes; control (I1), Irrigation based on irrigation requirement (I2) and I2 plus leaching requirement (I3), three soil depth of 25, 50, and 75 cm from soil surface at before and after irrigation event. The results of this study showed that in the root zone of the plant, the percentage of moisture content measured and estimated were relatively close, and showed that the HYDRUS-2D is able to simulate the soil moisture content in the root zone of the pistachio plant, and has this ability that it estimates conditions the soil moisture with highly accurate, during irrigation under different irrigation regimes at different depths of the soil. Model estimation process in the horizontal and vertical distribution of moisture, it was more than estimated in relation to the measured values. The statistical evaluations also showed that the accuracy of the HYDRUS-2D numerical model with respect to the coefficients of determination between 0.76 to 0.9 and RMSE ranged from 2.23 to 4.01, and the good ability of the model in predicting moisture content in field conditions.