Response of young super-high density table olive orchard (Manzanilla de Sevilla) to different water stress levels considering an accurate determination of endocarp development

Olive trees are extremely drought-resistant species. This particularity could be used to reduce water needs in regulated deficit irrigation scheduling. However, the yield response to water deficit is linked to the moment and the level of water stress imposed. Pit hardening has been commonly used as the stage to decrease irrigation, but it is not measured under field conditions. The aim of this work is to describe the impact of water stress conditions on yield response for table olive trees, considering an accurate determination of the endocarp development. The experiment was performed from the 2020 to the 2023 seasons on a two-year-old super-high density table olive orchard (cv Manzanilla de Sevilla). The three irrigation treatments (six repetitions) were: Control, no water stress conditions throughout the season in 2020 and 2021, and mild water stress to reduce vigour in 2022 and 2023; Regulated deficit irrigation (RDI), based on a moderate to severe water stress during pit hardening, using midday stem water potential measurements; and Rainfed. Endocarp development was established using the pit-breaking pressure throughout the 2021, 2022 and 2023 seasons. Water relations, vegetative growth, number of inflorescence and fruits, yield and fruit quality were measured during the experiment. Crown volume limited yield in Rainfed treatments but not in RDI, compared to Control. The number of inflorescences and inflorescence set was not affected in RDI and Rainfed, only reduced in severe water stress in 2023. RDI presented a similar yield response to Control, with a reduction of 50 % on applied water and a significant more negative midday stem water potential. The Rainfed trees were unsuitable for table production because rehydration did not recover fruit size enough to be commercial. Endocarp maintained the capacity of growing until the end of the season.