Tree development, yield and quality characteristics of fresh fruit and oil were evaluated under different water regimes for five years. The olive cultivars Ascolana Tenera, Kalamata, Nocellara del Belice, Maiatica and Itrana were tested in a factorial combination of four irrigation regimes: a rainfed control (T-0) and three treatments (T-1, T-2, and T-3) irrigated daily with a restitution of 33, 66, and 66% of crop evapotranspiration (ETc). In all years the lowest values of soil water content and xylem potential were detected in September and early October in To, during the phenological phase of rapid enlargement of fruit cells, while values were near field capacity during the irrigation season in treatment T-3. Growth parameters such as canopy, trunk cross section area and pruned wood showed little differences between the rain-fed control and the lowest irrigation level and between treatment T-2 and T-3 while differences were evident between the control and treatment T-2. Yield, fruit size, pulp-stone ratio and dry-matter content of fruit peaked at an irrigation depth of 66% of ETc, while higher volumes did not significantly increase yield, suggesting that complete replacement of water loss by the crop is not recommended. Only 'Kalamata' showed a higher yield of T-3 over T-2. Irrigation regimes did not affect the oil content calculated on dry-weight basis and the increase in oil per hectare was explained according to the increase in fruit dry matter content and number of fruit for 'Kalamata'. The fatty acid composition, sugar and acid content of the oil were not affected by irrigation, while the total polyphenol decreased up to treatment T-2. In the most irrigated treatment bitterness and pungency of the oil slightly decreased as compared with the rainfed control, while fruiting was unaffected by irrigation.
