Determining irrigation levels for a modern Israeli olive orchard: Towards maximum yields of high quality oil

Irrigators of modernized olive orchards are challenged to determine regional and cultivar specific water regimes that increase yield while not jeopardizing olive oil quality. We have investigated olive irrigation regimes, including severe deficit strategies, on two Israeli cultivars ('Souri' and 'Barnea') in a two year field experiment. Trees received 25, 50, 75, 100 or 125% of potential evapotranspiration throughout the dry seasons. Increasing irrigation increased stem water potential, vegetative growth, and olive fruit yield with the increases tapering off at application rates above the 75-100% treatments. Increases in oil yield as a function of increased irrigation were measured only after the second year of treatments, and only for the cultivar 'Barnea' that had been in an 'off' year during the first season in which the treatments lead to higher vegetative growth. Increasing irrigation lead to fruits with greater water content (lower oil percentage) as well as to relative decreases in total polyphenol content and to increased free fatty acids in the 'off' years. These preliminary results suggest a number of methods that could be beneficial to irrigation management including cultivar specific irrigation regimes and irrigation systems. Stress levels and water requirements are highly dependent on fruit load and best irrigation management should account for biennial bearing effects. Of specific interest is that oil quality of trees in 'off' years is particularly negatively affected by excess water. More work is necessary in order to determine optimum water stress scheduling (stress levels and timing) for best yield-quality combinations and to further develop methods for monitoring and maintaining water stress levels.