Effects of water deficit on the vegetative response, yield and oil quality of olive trees (Olea europaea L., cv Coratina) grown under intensive cultivation

An experiment was carried out in a young high-density olive grove (556 plants ha−1—Olea europaea L., cv Coratina) located in Southern Italy to evaluate the effect of different soil water availability on the vegetative and productive performances of olive trees also looking into the quality of the resulting oils. Trials were carried out over a 3-year period on trees subjected to irrigation and grown under rainfed conditions. Vegetative tree response, as shoot elongation and trunk diameter, was evaluated. Yield per plant, fruit characteristics, oil quality indices (free fatty acid content, peroxide value,UVadsorption at 232 and 270 nm, total phenols, -tocopherol content) were determined for both irrigated and non-irrigated treatments in the ‘on’ years 1997 and 1999 (6th and 8th year after planting, respectively). In the non-irrigated treatment soil matric potential (h) showed, during the spring and the summer of 1997, values on an average around or above −1.5MPa corresponding to a moderate water stress for olive plants. Particularly, h reached −2.0MPa in June 1997, at fruit set, affecting the number and the size of fruits and, so, the final crop level. As a matter of fact, the irrigated plants showed a production 76% higher than non-irrigated ones. Such finding confirms that water stress early in the season may strongly reduce the yield due to the effect on flowering and fruit set. On the other hand, mid-summer is defined as the less sensitive period for olive trees to water deficit. In this period it is possible to reduce or interrupt irrigation without a significant yield reduction as foreseen by the deficit irrigation strategies. Conversely, in 1999, after an ‘off’ year, the non-irrigated olive trees, in presence of h values ranging from −0.5 to −1.0 MPa, showed a great capacity of recovery, which led to vegetative and productive responses similar to those of the irrigated plants. From our results, it seems that soil water availability did not affect the examined oil quality indices. The lower total phenol content found in the oil of the non-irrigated plants in 1997 could be explained by the complex involvement of other factors influencing the polyphenols level.