Simulating water and soluble salts in deficit irrigation for some crops

One of the most efficient strategies for optimal use of water resources in arid and semi arid regions is the so-called deficit irrigation. Deficit irrigation by reducing number of irrigation or lowering volume of applied water in each irrigation may cause relative yield reduction per unit of farm. This may also cause salt stress in addition to water stress. In arid and semi-arid regions, this may reduce soluble salt leaching from the root zone, especial when growing salt sensitive crops, which causes further yield reduction. It is understood that in these regions leaching salts by providing adequate drainage is the normal practice to cope with water and salinity stresses. In this research using steady state calculation and management salt balance model (SaltMod), the effect of deficit irrigation was studied for four salt tolerant and salt sensitive crops in a long period (20 years) to find out the effect of salt and water stresses on yield of these crops. The salt tolerant crops were wheat and sugar-beet, and salt sensitive crops were corn and sugarcane which are important cultivated crops in Khuzistan province of Iran. Long time changes in soil profile and drainage water was also calculated and simulated. The results of this study showed that in a representative soil of arid-region (central Khuzistan area) with very high salt content upon installing drainage system and required leaching to bring root zone salinity to normal range (ECe < 4 dS/m), there is a good chance to continue wheat and sugar-beet cultivation with normal deficit irrigation (around 20 percent) for a long time. However it was not possible to use normal deficit irrigation for maize and sugarcane for more than a few years without complete crop loss. Increasing salinity of root zone showed the above process very clearly.