As a result of increased demand for healthy sources of fat for human consumption and the fact that olives are considered to be well-adapted to semiarid conditions, an intensive wave of olive planting has taken place in the last decade in many places worldwide [Food and Agriculture Organization (FAO), 1989]. Traditionally, olives have been cultivated in the Mediterranean region and many superior cultivars have been selected in most of the countries of this area. However, as a result of a continuously increasing shortage of tap water, mainly in semiarid areas, the irrigation of most new olive plantations is based on available low-quality sources of water all of which are characterized by a relatively high salinity (Wiesman et al., 2004). The relationship between saline water and olive cultivation has been intensively studied for many years and significant progress has been made in the understanding of this topic (Aragues et al., 2005; Bernstein, 1964; Gucci and Tattini, 1997; Maas and Hoffman, 1977; Munns, 1993; Wiesman et al., 2004). It is generally well established that saline conditions limit the vegetative and reproductive development of olives mainly as a result of interference with the osmotic balance in the root system zone and detrimental effects caused by specific toxic accumulation of chloride and sodium ions in the leaves (Benlloch et al., 1991; Bongi and Loreto, 1989; Hassan et al., 2000; Maas and Grattan, 1999; Tattini, 1994). Salinity is known to be a common limiting factor in semiarid areas, even when tap water is used, as a result of the high rate of water evaporation (Shalhevet, 1994).
The FAO (1985) classifies olive trees as “moderately tolerant” to salinity, suggesting a threshold electrical conductivity (EC) of the soil saturation extract between 3 and 6 dS·m−1. Although the threshold chloride and sodium ions toxic concentrations varied, as a result of different experimental conditions and tested genotypes, most studies concluded that they are ≈2 mg·g−1 of Cl− and 4 to 5 mg·g−1 sodium on a leaf dry weight basis, and it was suggested that injury is better correlated with sodium than with chloride (Al-Saket and Aesheh, 1987; Bernstein, 1975; Gucci and Tattini 1997; Klein et al., 1994). Recently, Aragues et al. (2005) reported on ‘Arbequina’ olive tree trunk growth reduction with chloride levels higher than 2.3 mg·g−1 and sodium levels higher than 1.5 mg·g−1.
Most reports have focused on the physiological mechanisms involved in olive tree response to saline soil and water conditions. As a result of the long time until olive trees reach maturity and their yielding phase, the majority of these studies has been carried out with solution cultures or greenhouse pot trials using young olive seedlings or plants and has focused on specific cultivars tested in various environmental conditions and cultivation practices. As a result of these experimental limitations, the results cannot be easily extrapolated to field conditions. A limited number of field trials analyzing the response of some specific olive cultivars using various cultivation practices and at different maturation stages have been reported in recent years (Aragues et al., 2005; Klein et al., 1994; Murillo et al., 2000; Wiesman et al., 2004). Even in these studies, relatively young trees were used and the sustainable effect of salinity on the olive trees was not studied for a significant period of time. In addition, salinity tolerance parameters are not well established, especially in mature trees, and were not well enough analyzed in field conditions. Thus, the actual impact of salinity on the yield of olives is uncertain. It is difficult to reach general conclusions and to predict the response of most olive cultivars to intensive cultivation under saline-irrigated semiarid conditions.
To support the rapidly growing olive industry in the semiarid south part of Israel and similar areas in the world, in 1997, we established a new special saline irrigation controlled experimental plot. Twelve selected superior local olive cultivars and cultivars from various Mediterranean countries were planted in this plot that was divided into two identical subplots: one was irrigated with tap water (1.2 dS·m−1) and the second was irrigated with moderate saline water (4.2 dS·m−1). In the present study, we aimed to evaluate and compare the vegetative and reproductive multiannual response of mature yielding trees of the 12 tested olive cultivars drip-irrigated with tap water and moderate saline water in a commercial orchard simulation study in a semiarid area.
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