Effect of controlled drainage and salinity of irrigation water on the performacce of sorghum crop yield, reduction of drainage water and water use efficiency

In conventional drainage system, water level in the plant root zone is lowered and salt in the irrigated area is washed away to the drain and transferred to another area. Controlled drainage is one of the management methods to control water level below the depth of the growing root zone. Discharging low-quality drainage water into other areas may have a devastating impact on the environment of many water habitats. In water table control methods, water loss from the region is reduced which means that more water can be used by soil. It is argued that the depth and quality of water table are effective in the growth and expansion of aerial branches of roots, quantity of the produce, reduction of drainage water and water Use efficiency. In order to determine these effects, a physical simulation model (lysimeter) was used to evaluate the impact of controlled drainage system and irrigation on water salinity of sorghum crop compared with free drainage. For this purpose, two treatments of drainage water level (free drainage (FD) and controlled drainage (CD)) and three treatments of irrigation water salinity (0.75 dS m-1, 3.4 dS m-1 and 4.8 dS m-1) with in three replications using18 lysimeters were employed. The results of the experiments show that unlike free drainage conditions in which soil moisture would be supplied only through irrigation and thus the sorghum plant will encounter shortage of moisture in the soil before the next irrigation,, in controlled drainage treatments soil moisture is supplied through capillary, water absorption is provided by the plant in potential level, which leads to increase of yield amounting to 3.5 time more than the free drainage. Moreover controlled drainage treatments could supply almost one third of needed water through water table. Therefore it is said that drainage water is diminished in this system at the same ratio. The mutual effect of water table and irrigation water salinity shows that higher moisture conditions in controlled drainage treatments will diminish the effect of salt accumulation in comparison to free drainage conditions; therefore irrigation water salinity has not made its real effect.