Assessing the impact of sustained and regulated deficit irrigation on field-grown olive cultivar ‘Zard’ (Olea europaea L.) in semi-arid condition

Abstract

Research has shown that moderate regulated deficit irrigation (RDI) can enhance the fruit and oil yield of olive trees in Mediterranean conditions. However, there is limited research on the effects of deficit irrigation on olive trees in marginal regions. To address this, a study was conducted on the Zard olive cultivar over two consecutive years. Six irrigation regimes were tested, including control (C) (100% ETc) during the growing season, sustained deficit irrigation (SDI1) at 75% ETc throughout the growing season, regulated deficit irrigation (RDI1) at 75% ETc from 4 to 9 weeks after full bloom, sustained deficit irrigation (SDI2) at 50% ETc throughout the growing season, regulated deficit irrigation (RDI2) at 50% ETc from 4 to 9 weeks after full bloom, and regulated deficit irrigation (RDI3) at 50% ETc 2 weeks before harvest. The results showed that sustained and regulated deficit irrigation negatively impacted flower number and perfect flowers in inflorescence, except for RDI3. The study found that the fruit set was not significantly impacted by the irrigation treatments RDI1 and RDI3 compared to the control. However, the irrigation treatment of SDI2 resulted in the most significant reduction in both fruit weight and pulp-to-pit ratio. Fruit yield and oil content did show significant differences among all treatments. Overall, the study showed a 25% reduction in water usage during the 4 to 9 weeks after flowering or 2 weeks before harvesting did not significantly affect fruit yield compared to the control treatment. A minor reduction in applied water (RDI1 and RDI3) is recommended for semiarid regions (excluding Mediterranean regions) to achieve high fruit and oil content.