Phenology, Morphology and Physiology Responses of Deficit Irrigated 'Koroneiki' Olive Trees as Affected by Environmental Conditions and Alternate Bearing

Climate change is affecting water resources in the Mediterranean region. In olive orchards, irrigation water use efficiency could be increased by accounting for trees' alternate bearing behaviour and growth-stage sensitivity to drought. The main objective of this study is to examine olive tree phenology, morphology and physiology in "on" and "off" productive years for the improvement of irrigation scheduling. A regulated (RDI) and a sustained (SDI) deficit irrigation treatment were applied in a 'Koroneiki olive orchard in Cyprus. Flowering occurred on 11 May 2019 and on 27 April 2021, which was caused by the lower temperatures in 2019. The K-c for the irrigation season, computed from daily water balance observations, was 0.37 in 2019 (38% canopy cover) and 0.41 in 2021 (62% canopy cover). Irrigation treatments did not significantly affect plant morphology and stem water potentials. In "on" years, shoot elongation ceased early in the season and stem water potential towards the end of September (-4.0 MPa) was lower than in the "off" year. Stem water potential recovery in the September of the "off" year indicated that irrigation could be less than 35% ETc in early fall. Water savings in RDI were 24-32% in "on" and 48% in "off" years relative to SDI, with no statistically significant effects on olive yields.