SIMULATION OF THE DRIP IRRIGATION MANAGEMENT PRRACTICES AND THEIR EFFECTS ON THE SOIL PROPERTIES BY USING « HYDRUS » MODEL

Abstract

Enhancing the wet characters of the root zone under drip irrigation is one of the objectives of the irrigation designers and researchers, in the goal to increase production and yield of agricultural crops. During drip irrigation, the moisture content of the root zone rises, thus reducing the capillary forces between the water and the soil particles, so that it makes root extraction easier to obtain its water needs. Information about temporal evolution of the wetted soil volume can be helpful in establishing the optimal emitters spacing and the duration of irrigation, for the volume of soil where the main crop roots are located; it is of great importance in realizing the full potential of drip irrigation technology. The mathematical equation that governs water transfer in porous soils with specific conditions is the Richards’s equation. In this research, numerical simulations were performed with HYDRUS-2D/3D, this model numerically solves Richards equation, to investigate the influence of different irrigation management and design strategies on the soil water dynamics, HYDRUS-2D/3D uses a numerical finite element approach in plan (where the flow region is divided into a triangular (2D) network. The corners of these elements are taken to be the nodal points. In addition, HYDRUS was used to simulate the impact of 8 discharges rate application (1, 2, … 7, 8 L/h) With difference distances between drippers ( 20, 30 ,50cm ) according to a frequency ranging from one to seven days in the climatic conditions of the study area to predict the water content mode in the root zone of tomato crop. Furthermore, to validate the program and choose the best strategy for managing drip irrigation, model accuracy was evaluated against experimental data in the field. The experimental study was carried out in the private farm in Chlef. The field is geographically located at coordinate of 1° 27' 20'' E, 36° 13' 60'' N. Soil moisture was measured using a TDR where several water content readings at different depths in the root zone were carried out during the growing season of tomato crop. The first objective was to validate the HYDRUS-2D / 3D for two simultaneouslyworking surface drippers with sandy-loam texture. Root-mean-square-error (RMSE) was employed such as statistical analysis to evaluate the performance of the HYDRUS-2D/3D model and to test the goodness of fit between simulated and observed soil volumetric water content values. The RMSE value range between 0.0057 and 0.043 m3.m-3. These results Simulation of the drip irrigation management practices and their effects on the soil properties by using “HYDRUS” model IX demonstrate the reliability of HYDRUS2D/3D in the simulation of volumetric water content values (VWC) compared to those measured in the field. The second objective was to simulate various irrigation strategies using the validated model to optimize lateral and the vertical leaching water movement. According to the model studies, emitter discharge rates affects significantly the wetting pattern shape, with a large discharge rate, the width of an isoline increases, while the depth of the isoline decreases, while the reverse is true at small flow rates. From the results of studies on the simulator, it is recommended to use a dripper of 3 L / h with irrigation every three days and at 50 cm between drippers to obtain a homogeneous distribution of moisture in the wet area (optimal strategy) while avoiding problems of saturation or lack of moisture in the active roots area, thus the wet diameter does not exceed 50 cm vertically. This has been proven in the field by the high yield of tomatoes under this strategy which has recorded 30% rising compared to other strategies.