Effects of irrigation on yield and oil quality of different olive cultivars grown in semi-arid conditions of Tunisia

To understand the relations between water availability existing in semi-arid conditions of central Tunisia and yield components of olive trees, a field experiment was carried out to study the behavior of local and foreign cultivars under two irrigation regimes (small water supply 10% ETc which was closed to rain-fed condition and full irrigated 100% ETc). The trial was carried out over a 2-year period where the two different irrigation treatments were applied. Yield, fruit characteristics, oil quality indices (free fatty acid composition, acidity, UV absorption at 232 and 270 nm, total polyphenols, chlorophyll) were determined for both irrigated and non-irrigated treatments. Maximum production recorded over the two growing season (on year followed by off year), were given by 'Picholine', 'Chemlali', 'Coratina' and 'Koroneiki' irrigated with only 10% ETc which, noted a biannual yield varying between 16 kg tree-1 (3246 kg ha-1) and 34 kg tree-1 (6936 kg ha-1). Conversely, 'Chetoui' showed the lowest biannual yield which did not exceed 8 kg tree-1 (1600 kg ha-1) even for trees which received 100% ETc. The typical alternate bearing behaviour of this specie alters the producing pattern of the plant making less evident water effect. On the other hand, water supply caused an increase of the fruit weight and the pulp:stone ratio for all cultivars while it did not affect the oil chemical parameters. The results showed that 'Picholine', 'Chemlali', 'Coratina' and 'Koroneiki' showed an economical satisfactory yield and interesting oil characteristics (low palmitic acid and high oleic acid) even under semi-arid conditions.