The Effects of Irrigation Efficiency and Uniformity Coefficient on Relative Yield and Profit for Deficit Irrigation

To avoid constructing expensive hydraulic structures for implementing new water resources, a deficit irrigation project may be designed to optimise the use of the available water resources. Previously, irrigation efficiency and uniformity coefficient have not been considered quantitatively. In fact, efficiency is a very significant factor in optimisation analysis, and the potential for increasing irrigation efficiency is one of the key reasons for deficit irrigation. In this paper, the influences of irrigation efficiency under full irrigation condition ηf on the performance of deficit irrigation, and the effects of deficit irrigation on improving the irrigation efficiency under deficit irrigation ηd have been considered for four crops of winter wheat, spring barley, maize, and sorghum in an arid region of Iran. Furthermore, the combined effects of irrigation efficiency and uniformity coefficient on deficit irrigation were investigated. Results showed that considerable improvements can be achieved in water use efficiency under this concept. Some mathematical relationships were derived to show the quantitative increase in irrigation efficiency under deficit irrigation. These results showed that the performance of deficit irrigation is highly dependent on ηf, such that lower ηf values result in higher allowable water reduction level and also more field income. By combined analysis, water reductions for sorghum and barley were found to be economically feasible at values of irrigation efficiency lower than 1·0, while water reduction for maize was not economically feasible at irrigation efficiencies greater than 0·6. Water reduction for wheat was economically feasible at irrigation efficiencies of 0·6 or lower.