The Effects of Controlled Drainage on Soybean Yield and Improving of Irrigation Water Productivity

Despite daily increasing water requirement, it is necessary that environmental adverse effects of each project be controlled, so revision of ability of traditional drainage systems is unavoidable. Controlled drainage is an environment friendly water management practice that conserves water and reduces nitrogen losses through reduced drainage water volume. This research was conducted in order to determine the controlled water table depth and its effects on irrigation water productivity and yield of soybean crop, by using lysimeter in 2008 in Shahrekord University. A completely randomized experimental design with three replicates, consisting of four water table treatments were used: Free Drainage/ traditional drainage (FD) as control, and depth of water table in 60-65, 40-45 and 20-25 cm from the soil surface, which named CD60,CD40 CD20, respectively. Results of variance analysis showed that the effects of drainage treatments were significant on yield components. The highest yield observed in CD60 treatment (2774 kg/ha). Lack of rapid depletion in this controlleddrainage treatment may caused water and nutrient be more available for plant. The least yield obtained in CD20 treatment with the average of 1798 kg/ha. It may be explained by water logging in the most part of root. Also lack of oxygen and creating the situations to denitrification limited efficient use of water and nutrients for plant. The maximum and minimum of irrigation water productivity obtained in CD60 and CD20 treatments. The seed production rates of these treatments were 0.45 and 0.29 Kg/m3, respectively, in comparision 0.4 in control treatment.