Development of a nonlinear programming model optimal cropping pattern based on deficit irrigation scenarios

Obtaining appropriate levels of deficit irrigation is necessary to improve water productivity and performance of irrigation networks in deficit irrigation conditions. This study was carried out to develop a nonlinear programming model for determination of an optimal cropping pattern in deficit irrigation conditions. A non-linear model with the objective function of economical water productivity index (Net profit to water consumption ratio) was combined with a crop growth model and it was evaluated using the data of Shahid Chamran irrigation network. Results showed that the highest cultivation area in all scenarios is related to wheat crop. The wheat cultivation area for the 10, 20 and 30 percent deficit irrigation were estimated to be 674, 949 and 1362 ha, respectively. The increased cultivation area in 30 percent deficit irrigation scenario was estimated 92 percent as compared to the full irrigation scenario. The lowest cultivation area in the network was for sunflower with an area of 189 hectares (in 30 percent scenario). The results of this study for the 10 percent scenario indicated that the overall economical water productivity of the network can be increased up to 19% by managing cropping pattern as compared to the full irrigation scenario. While in the 20 and 30 percent deficit irrigation scenarios, the economical water productivity index values increased 21 and 23 percent respectively by implementing optimal cropping pattern. Also studies show that the different combinations of deficit irrigation scenarios for the crops could present different results. Accordingly, the overall water productivity of the network can be increased to a maximum of 15250 Rls/m3, if 10 percent for broad bean and bean, 20 percent for sunflower and potatoes and 30 percent deficit irrigation for wheat are considered.