UTILITY OF HYDRUS-2D IN MODELING PROFILE SOIL MOISTURE AND SALINITY DYNAMICS UNDER SALINE WATER IRRIGATION OF SOYBEAN.

A field experiment was conducted to study ways to recycle marginal quality saline drainage water for soybean irrigation in the West Nile Delta Region of Egypt. Irrigation treatments were fresh canal water with an electrical conductivity (EC) of 0.4 to 0.7 dS m-1 (T1, Control), drainage water with EC 6.0 to 8.0 dS m-1 (T2), mixed canal and drainage water with EC 2 dS m-1 (T3), and alternating drainage and canal water in rotation (T4). HYDRUS-2D was used to simulate profile soil moisture and salinity dynamics under four irrigation treatments. Irrigation with saline drainage water tended to depress soybean water consumption. Measured mean values during the growing period of soybean water consumption were 46.3, 36.2, 43.4, and 42.0 cm for irrigation treatments T1 to T4, respectively. These were reasonably close to corresponding values simulated using HYDRUS-2D. Use of saline drainage water increased the 0-100 cm depth-averaged soil solution salinity at harvest by 1.6, 13.9, 5.8, and 13.3 times the value of 0.8 dS m-1 before planting for treatments T1, T2, T3, and T4, respectively. The simulated averaged daily soil solution salinity values for the 0-100-cm depth showed expected patterns and trends over the growing season. Depth averaged simulated soil solution salinity values at 20-cm intervals to 100 cm at harvest matched corresponding measured values reasonably well. Soybean yield reductions were 0.50, 0.20, and 0.31 for T2, T3, and T4, respectively, compared with T1 (control). Decreases mirrored the order of increasing soil solution salinity values for the treatments with saline water. Overall, results indicated a reasonably good potential for recycling of marginal quality saline drainage water and for using HYDRUS-2D as a tool in developing or evaluating strategies and techniques for this purpose in the West Nile Delta of Egypt.