Yield and oil quality of intensively trained trees of three cultivars of olive (Olea europaea L.) under different irrigation regimes

The aim of the present study was to evaluate the qualitative and quantitati ve yield response to irrigation of olive in southern Italy. The olive cvs K alamata, Ascolana Tenera, and Nocellara del Belice were tested in a factori al combination with four irrigation levels: a rain-fed control (T-0) and th ree 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 rem ained near field capacity in treatment Tg With no difference with respect t o treatment T-2. In T-0 and T-1, the soil moisture decreased during the sum mer with the lowest value (20.8%) found in T-0 on 12 August, after which ra infall restored the soil moisture to held capacity. During the season the r elative 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 t he pulp-stone ratio and the quantity of triglycerides accumulating in the f ruits were similar for all treatments. The fatty acid composition of the oi ls was not affected by irrigation, while there was a decrease in the conten t of polyphenolic substances with irrigation. This decrease could be attrib uted to different enzymatic activity, caused by the water deficit, rather t han to different degrees of fruit ripening. The decrease of polyphenols did not influence the oil quality in terms of organoleptic parameters or oil s helf-life.