Yield and quality of two rainfed olive cultivars following shifting to irrigation

Six year old `Frantoioʹ and `Leccinoʹ olive plants were subjected to different water regimes for three years to assess yield and quality performance in response to the onset of irrigation. Irrigated plots received 33, 66 and 100% of crop evapotranspiration rate (ETc), accounting for 173, 212 and 278.mm, in 1999, 2000 and 2001 respectively ± while no water was applied to treatment 0. Little rain occurred throughout the summer of 2000 and 2001 seasons and mean air temperature was in both years higher than in 1999. Midday xylem water potential of non-irrigated plants was only slightly decreased, however. Stem diameter and canopy volume of `Frantoioʹ were enhanced by irrigation, while `Leccinoʹ showed a response only in terms of the latter variable. The response of both vegetative and reproductive variables grouped in two classes, with the rain-fed control not different from 33 and treatment 66 and 100 being almost identical. Yield to water supply relationship was curvilinear in the first year, with little yield increase in response to 100% ETc. In 2000, a non-bearing year, yields were lower and the trends were linear, with a gentle slope. In 2001, much higher yield were achieved overall and `Frantoioʹ still responded in a linear fashion while `Leccinoʹ reached a plateau under 66. Water use efficiency reached top values in excess of 4.kg l-1 in 2001 featuring a typical decreasing trend from rainfed to 100 for both cultivars. Irrigation efficiency peaked at the level of 66 for `Frantoioʹ in all years and for `Leccinoʹ in 2001. The latter however was more efficient under 33 ETc during the first two years. A complete replacement of water loss by plant is to be recommended only in situations of unrestricted water supplies, and `Leccinoʹ should be preferred when water is costly or scarce. Oil quality was little affected and only total polyphenolic content was modified by irrigation, to an extent not capable of influencing oil storage capacity.