Deficit irrigation during the oil synthesis period affects olive oil quality in high-density orchards (cv. Arbequina)

The effect of 4 irrigation doses during the oil synthesis (from the end of August until harvest) on virgin olive oil quality was evaluated in high-density orchards of the cv. Arbequina. The control treatment (T1) kept a humidity bulb close to the field capacity. Three deficit irrigation treatments (T2, T3 and T4) were applied during oil synthesis, providing 68, 40, and 17 % of T1, respectively. The olive fruits were harvested and their oil was extracted and analyzed. Plant water status (Wstem), oil production, fruit characteristics and fruit temperature were measured. During 2012 mild water stress was produced in a less irrigated treatment T4 (mean Wstem -2.39 MPa) and deficit irrigation did not affect most of the oil quality parameters. However, in 2013 a higher stress was observed in T4 (-4.76 MPa) and the oil showed higher values for K-232, K-270, carotenoids, chlorophylls, alpha-Tocopherols, beta-Tocopherols, total tocopherols, palmitoleic acid, estearic acid, and linoleic acid, but lower oil stability than T1. In 2013 hydroxytyrosol, vanillic acid, acetoxypinoresinol, ferulic acid, luteolin and apigenin contents were higher under low stress treatment, producing oil fruitier and more pungent. The total phenol content was the most sensitive oil parameter to water stress and in both years it was significantly higher in the most irrigated treatments. Increasing stress conditions (lower Wstem) coincided with lower values for oleic, phenols and oxidative stability. However, this stress induced higher vitamin contents (A, E and F). Considering that 'Arbequina' oil is characterized by low values for total phenol, oleic acid and oxidative stability, high tree hydration ( > -2.21 MPa) should be maintained during oil synthesis for maximum oil production, oxidative stability, oleic acid and high phenol content.