Effects of Irrigation and Potassium Fertilizer on Sugar Dynamics and Ripening in Arbequina Olives Across Harvest Seasons

Climate variability may influence olive ripening and sugar composition, complicating irrigation and nutrient management. We hypothesized that reduced irrigation would increase glucose concentrations in ‘Arbequina’ olive pulp, with responses varying according to potassium supply and harvest season. Sugar profiles and ripening-related physicochemical parameters were evaluated in ‘Arbequina’ olives across three harvest seasons (2021–2023). A 15-run Box–Behnken design combined three levels each of irrigation, potassium fertilization, and foliar copper application. Fruits were sampled monthly from May to July in each harvest season. Glucose was the predominant sugar and varied among seasons, reaching 28.12 mg g−1 in July 2021. Response surface models predicted maximum glucose concentrations of approximately 30 mg g−1 at the 75% irrigation level and 100–123.6 kg K2O ha−1 in May 2021 and 2022. Kernel principal component analysis differentiated samples by harvest month and season. Associations between the a* color coordinate and sugar concentrations were strongest in 2022 but were not consistent across seasons. Overall, the findings highlight seasonal variation in sugar composition and ripening-related physicochemical parameters. This seasonal dependence emphasizes the need to interpret agronomic management effects within their environmental context and supports the combined use of sugar profiles, physicochemical indicators, and multivariate analysis to assess olive fruit ripening.