Optimal Allocation of Irrigation Water Using Water Production Function

Water production function helps in selecting alternative levels of water for getting maximum output under a given irrigation water supply level. This paper reports the development of water production functions for wheat crop using surface and sprinkler irrigation methods. Twelve irrigation levels and three replications were selected for both the irrigation methods. Under surface irrigation, the irrigation levels were selected based on IW/CPE ratio of 0.40, 0.55, 0.70, 0.85, 1.0, 1.15, 1.30, 1.45. 1.60, 1.75, 1.90 and 2.05. In the case of sprinkler irrigation, each crop strip grown on either side of the sprinkler line was considered as a separate irrigation treatment. Quadratic production function was found to be the best fit for surface and sprinkler irrigation methods. Water required for obtaining maximum yield in case of surface irrigation was 380mm whereas in case of sprinkler irrigation it was 338mm. Linear cost functions were developed for both the irrigation methods using electrical and diesel pump sets for developing a model for optimal allocation of water. The optimal allocation model reduced the agricultural water requirement from 380mm for maximum yield to 349mm for maximum net profit in case of surface irrigation and 338mm to 298mm in case of sprinkler irrigation using the diesel pump set without any significant difference in crop yiela. The total cost of water and irrigation machinery inchiding the labour cost, and repair and maintenance cost for the surface irrigation method was computed as Rs. 7.55/ha-mm and Rs. 1l.89/ha-mm while using the electrical motor and diesel motor pump-sets, respectively; whereas for the sprinkler irrigation method, the corresponding costs were Rs. 25.51/ha-mm and Rs. 35.13/ha-mm. Further the highest net returns obtained by using this model were Rs. 16,894/ha and Rs. 10.870.8/ha in case of the surface and sprinkler irrigation methods, respectively.