Modeling Soil Wetting Patterns under Pulsed Drip Irrigation by Dimensional Analysis Method and Comparison with HYDRUS-2D Numerical Model

The optimal design, operation and management of drip irrigation systems relies significantly on selection of a suitable combination of emitter discharge rate, emitter and lateral spacing, root depth and soil hydraulic properties that should be in consistent with root growth pattern in the soil for delivering required amount of water and nutrition to the plant. Modeling soil wetting pattern is more practical and easier than the conducting laboratory or field measurements. In this study, an empirical model was developed to predict the dimensions of the wetting pattern under pulsed drip irrigation using dimensional analysis method. The main inputs of the proposed model are emitter discharge rate, saturated hydraulic conductivity, total volume of applied water and pulse ratio.  Experimentations included determination of the maximum depth and width of the wetting pattern after water application under different combination of pulses in a clay soil. The treatments were consisted of three pulses (P2, P3, P4) and two Off-Time durations (T1, T2). The predicted values of wetted depth and width by the empirical model and the HYDRUS-2D model were compared with the observations. The coefficient of determination parameter for the measured and estimated wetting pattern dimensions that obtained from empirical model was 0.94 and 0.93 and for numerical model was 0.95 and 0.97, which indicates good accuracy of the models. The results of the T-test analysis indicated that the empirical and numerical model simulated values were not significantly different (with a probability of 99.5%) from the observed ones. Although, on the basis of RMSE, ME and EF parameters the HYDRUS-2D model performance was better than the proposed empirical model but due to the simplicity of use and requiring less number of input parameters, it is recommended to use the developed empirical model to predict the wetting pattern as required in the design of drip irrigation systems.