Effects of deficit irrigation on ‘Koroneiki’ olive tree growth, physiology and olive oil quality at different harvest dates

Agricultural water demand in the Mediterranean region is expected to increase due to climate change. The application of deficit irrigation practices may improve the efficiency of water use in orchards, by accounting for changes in environmental conditions and in the tree growth. The main goal of this study was to improve our understanding on the effect of deficit irrigation on physiology, morphology, yield, and oil quality of ‘Koroneiki’ olive trees. The effect of two deficit irrigation treatments and three harvest dates on olive yield and oil quality were investigated in a 17-year old, low-density ‘Koroneiki’ orchard in Cyprus, during a high crop load year. For the sustained deficit irrigation (SDI) treatment 70% ETc was applied over the irrigated period, while the regulated deficit irrigation (RDI) consisted of 70% ETc during water-stress sensitive growth stages (shoot growth, flowering, bud initiation) and 35% ETc during water-stress tolerant growth stages (pit hardening, oil accumulation). Environmental conditions and volumetric soil water content of the 70-cm rootzone were monitored. A Kc of 0.37 was derived for the irrigated period from daily water balance computations, excluding rain days. No significant effects of the two irrigation treatments were found on morphology, physiology, fruit yield and oil quality. Midday stem water potential reached − 4 MPa in September as a result of increasing fruit load. Leaf conductance ranged between 65 and 228 mmol m-2s-1, with highest values obtained under high soil water conditions and a vapour pressure deficit of 3.6 kPa. Yields were approximately 9 tons ha-1 in both irrigation treatments while water productivity was 1.4 and 1.0 kg oil m-3 irrigation water in SDI and RDI, respectively. Maximum phenolic content was found in early December, reaching on average 202 mg kg-1 oil in both irrigation treatments. Overall, irrigation water use in RDI was 32% less than in SDI, whereas oil quality was only affected by the harvest date.