Simulation studies on use of saline water for irrigation in semi-arid environment

Diagnosis in water management is being supported more recently with the help of physically based numerical models simulating the water and salt balance. This paper presents computer aided water management for interpretation of field experiments and for predicting future scenarios. An agro-hydrological model was first calibrated and validated for local conditions (Hisar, India) and subsequently used for predicting long term impacts. Various water management response indicators are used to interpret the impact of both medium (4 years experimented) and long term (next 10 years simulated) use of such saline waters on soil environment and sustainable crop production. The present simulation study showed that the prolonged use of high salinity waters (EC greater than or equal to 7 dS/m) with normal irrigation (preplant with 8 cm canal and postplant with 6 cm saline water) in semi-arid areas should be restricted on medium to heavy textured soils because high salinity proved detrimental to relative transpiration and ultimately to the grain yield. Salinity hazard index was inflated by 92 to 146% and relative transpiration was suppressed by 40 to 60%. Consequently, simulated wheat and pearlmillet crop yields were down to 37 and 18 q/ha for 7 dS/m water and to merely 25 and 13 q/ha for 14 dS/m water during 15(th) simulated year, compared to 62 and 31 q/ha realized under canal water in the beginning in 1989-90. However, simulations showed that prolonged use of marginally saline water (EC = 3.5 dS/m) under normal irrigation and even of moderately saline water (EC = 7 dS/m) under heavier irrigation (12 cm canal pre- and 10 cm saline postplant water depths), on such medium to heavy textured soils, with a sub-surface drainage system, need not be forbidden. Reasonably good crop yields could still be obtained in the range of 46-48 and 21-22 q/ha for wheat and pearlmillet crops. Drainage effluent of 7.6 dS/m salinity from using 7 dS/m water continuously over 14 years indicates sustainability in using such moderate quality waters. But for highly saline waters (EC greater than or equal to 14 dS/m) such long term usage needs to be restricted on such soils in semi-arid areas where even the heavier amounts of irrigation failed to depress salinity hazard and elevate crop transpiration to any noteworthy levels, grain yields remaining below 30 and 15 q/ha for the two crops.