Yield response of a mature hedgerow oil olive orchard to different levels of water stress during pit hardening

Resumen

Drought sensitivity in olive trees varies throughout the season. The yield response to drought needs to consider the final use of the fruits and harvest date. In Mediterranean climates, the oil accumulation tends to occur in a period of low evaporative demand and during the rainy period. The aim of this work was to evaluate the effect of water stress during pit hardening on the yield components of oil olive trees. The experiment was conducted during three seasons (2017–2019) in a mature hedgerow olive orchard (11 years-old, Arbequina cv). The experiment design was a randomized completed block with 4 repetitions of 4 different irrigation treatments. Treatments were: Control, no water stress throughout the season; Regulated deficit irrigation (RDI)-1, moderate water stress during pit hardening and total recovery after the last week of August; RDI-2, same as RDI-1 but with severe water stress and partial recovery; and sustained deficit irrigation (SDI), constant applied water rate and the same seasonal water than RDI-2. The irrigation scheduling in RDIs were based on the frequencies of the trunk growth rate. No significant differences were found in fruit and oil yield between treatments. There were a significant relationship between water status measurements and fruit and oil yield. Part of the decrease in fruit yield with midday stem water potential (SWP) was related to fruit moisture, as no significant fruit drop was found. Only conditions of water stress in 2017, before the end of endocarp size, were related to a great reduction of fruit volume and, consequently, with fruit and oil yield. The relationship between the percentage of oil in dry weight and SWP was quadratic in different phases. Such relationships could help quantify the water stress level in these periods to maximize oil accumulation.