Evaluation of regulated deficit irrigation strategies for oil olives: A case study for two modern Israeli cultivars

Profits from olive oil production are expected to benefit from regulated deficit irrigation (RDI) regimes designed to optimize yield and oil quality with minimal inputs of water. We evaluated a number of potential strategies for implementing RDI including choosing phenological periods for reduced irrigation, use of midday stem water potential (SWP) for scheduling, considering fruit load, and irrigation to reach optimal fruit water content at harvest. We base our discussion on the potentials and challenges of practical commercial RDI regimes on results from a 6-year orchard experiment on two olive oil cultivars used in intensive orchards ('Barnea' and 'Askal') in Israel, focusing on attempts for long-tern optimization of yield and oil quality. Results showed a general trend of increased water productivity as a function of reduced irrigation but since yields tended to be reduced when irrigation was decreased, there was not a clear benefit of RDI over sustained deficit irrigation. The exception to this was a treatment based on SWP where water application was reduced by some 40% compared to irrigation regimes bringing highest yields, and a non-significant accumulated yield reduction of less than 15% after 6 years in both cultivars. Oil quality, measured in terms of free fatty acids and polyphenol content, was often improved when irrigation was decreased, with no dependence on the seasonal timing of deficit amounts and increased tree water stress.