Determination of suitable deficit irrigations strategies by maximizing social profit

This paper is part of a research project study in district of Khorasan entitled: “determination of suitable deficit irrigation strategies by maximizing social profit”. A chance constraint linear programming model was developed in which technical coefficients were determined differently from conventional linear programming approach. Model was run with three levels of water use efficiencies (65, 45 and 35 percent), with and without water supply risk and sugar beet. Forty different water stresses were imposed in different growth stages of sample crops. Results showed that, water use efficiency was more than 35 percent in sample farms. Reducing water use in an activity does not necessarily result in reducing farm water use. In addition, results showed that optimal allocation of irrigation water at the farm level happens when marginal return of water is the same not only in all growth stages of a crop but also in different growth stages of competing crops grown in the farm. Moreover, the findings indicated that net social profit could be increased when sugar beet (with negative social profit) is included in the model with considerable stress in all its growth stages. Social profits were increased by decreasing uncertainty of available water supply along with raising water use efficiency. The finding also indicated that in determining irrigation water price it is necessary to consider social profit as well as water use efficiency at the farm level. Finally, there is limited scope for increasing water price from social point of view.