The aim of the present study was to evaluate the qualitative and quantitative yield response to irrigation of olive in southern Italy. The olive cvs Kalamata, Ascolana Tenera, and Nocellara del Belice were tested in a factorial combination with four irrigation levels: a rain-fed control (T-0) and three treatments (T-1, T-2 and T-3) irrigated daily with an amount of 33%, 66% and 100%, respectively of crop evapotranspiration. Soil water content remained near field capacity in treatment Tg With no difference with respect to treatment T-2. In T-0 and T-1, the soil moisture decreased during the summer with the lowest value (20.8%) found in T-0 on 12 August, after which rainfall restored the soil moisture to held capacity. During the season the relative water content in the leaves was higher in the irrigated treatments than in the rain-fed control. Yields were higher in all the cultivars with irrigated treatments than in the rain-fed control. The yield increase with treatment T-1 in 'Nocellara del Belice' was 200% compared with the rainfed control and with T-2 in 'Ascolana tenera' and 'Kalamata' the yield was 233% and 47% greater than in the control. The higher oil yield obtained in the irrigated treatments was mainly due to the increase in fruit yield, since the pulp-stone ratio and the quantity of triglycerides accumulating in the fruits were similar for all treatments. The fatty acid composition of the oils was not affected by irrigation, while there was a decrease in the content of polyphenolic substances with irrigation. This decrease could be attributed to different enzymatic activity, caused by the water deficit, rather than to different degrees of fruit ripening. The decrease of polyphenols did not influence the oil quality in terms of organoleptic parameters or oil shelf-life.
