Effects of irrigation and fertigation on tree growth, yield and oil quality of olive cultivars in south Tunisia

Olive tree is traditionally cultivated under semi-arid climates where water is a scarce resource and very poor nutrient levels are present in the soil. Sufficient water supply and adequate fertilization are nowadays applied to olive orchards managed under intensive conditions to satisfy the water demand of the orchard and the nutrient level of the tree. The aim of this work was to evaluate the effects of irrigation and fertigation (combined treatment) on olive trees under intensive conditions. The amount of fertilizer applied was 3 kg ha^-1 week^-1 for the bud break to fruit set period, 3.6 kg ha^-1 week^-1 for fruit set to pit hardening and finally 2.9 kg ha^-1 week^-1 for fruit set to pit hardening. An experiment was carried out at the Experimental Field 'Taoues', southern Tunisia, to investigate the influence of irrigation used alone or combined with fertigation on three olive oil cultivars ('Chétoui', 'Chemlali' and 'Koroneiki') for four consecutive seasons. Three treatments were applied: trees under rain-fed conditions (RF), trees irrigated with 50% crop evapotranspiration (ET_c) (I) and finally trees that received 50% ET_c and a supply of fertilization (IF). Tree canopy volume, yield and oil composition were determined. Results showed that the olive trees that received irrigation applied alone or combined with fertigation developed larger canopies after four treatment years. 'Chétoui' showed the lowest biannual yield, which did not exceed 1530 kg ha^-1. Fruit weight was more affected by fertigation than by irrigation applied alone. Water availability and fertilization did not affect olive oil composition, except for total polyphenols, which decreased.