Optimization of Water Use in Deficit Irrigation Management under Rainfall in Mazandaran Province

In the current study, economic analysis of deficit irrigation was conducted for a Thomson orange orchard in Sari in two scenarios of considering applied water including 1-only irrigation water, 2- irrigation water plus rainfall. Production and cost functions were modified in water and land limitation conditions using English method. These functions were determined for without and 4 days irrigation interval using mathematical analysis and aimed to obtain the maximum net income. Results showed that when rainfall occurs, irrigation water plus rainfall should be considered as applied waer in production and cost functions. In addition, when there is no water limitation, the highest net income per unit of land is obtained from Wm that is 277.4, 315.6 mm for without and 4 days irrigation interval. Production for this situation is 51.3 and 57.4 ton/ha, respectively. In water limiting condition, the optimum water depth (Ww) is 257.6 and 287.9 mm that causes more than 26% saved water. If there is also land limiting in this situation, the net income per unit of land decreases 3.3 and 4.1 percent. However, the net income per unit of water increases 4.2 and 5.1 percent. If there is no land limiting in this situation, by irrigation equivalent to full irrigation, the net income per unit of land increases 7.5 and 9.2 percent. This status obtains the highest net income per unit of water use. According to the current resutls, having an irrigation schedule causes 12% increase in production and if it is associated with deficit irrigation, causes 5% more increase in net income.