Olive trees are drought-tolerant ones cultivated in several regions around the world to be used as olive oil and conserve. Regarding threats like water scarcity and drought, supplying the required irrigation water is one of the major problems in expanding olive cultivation industry. Deficit irrigation is a proper method in horticulture which is offered for improving water use efficiency. The present research was conducted in Kermanshah province, Iran. The irrigation regimes are as follows: T1: full irrigation, T2: 100% of full irrigation during the growing season plus 25% irrigation during pit hardening, T3: 100% of full irrigation during the growing season plus 75% irrigation from the beginning of pit hardening up to Harvesting, T4: 100% of full irrigation during the growing season plus 25% irrigation during fruit color change, T5: T2 + T4, T6: 50% of full irrigation, and T7: no irrigation. The results showed that vegetative growth, fruit yield, and oil yield were affected by the irrigation regimes. The highest fruit yield and oil yield were observed in the ‘Mission’ trees which were treated by T5. As a result, deficit irrigation can be performed without any damages to the trees and this can save irrigation water in olive orchards.
