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Effects of drought and salinity on water status, growth and physiological activity of olive can be temporary or permanent and may impact olive production sustainability, especially in southern Mediterranean areas. Tunisia has a Mediterranean climate with high temperatures and low summer rainfall. Thus water stress problems are likely to be more severe for cultivated olive trees. In addition, the reduction in the availability of good quality irrigation water will increase the use of saline water. Olive trees are able to tolerate low soil water availability and quality and develop physiological adaptations to cope with water and salt stress. However, these adaptation strategies are limited and permanent damages can be observed. The permanent effects caused to olive leaves due to drought, and the capacity of irrigation with saline water to avoid these impacts is not well known. The aim of this work was to compare olive leaves performance after a severe drought with, and without, irrigation and to assess recovering capacities after a rainy period. Moreover, irrigation water quality effects were also evaluated. The results showed that, photosynthetic rate was very low for rainfed plants, during drought, as compared to irrigated ones. After re-watering, rainfed trees photosynthetic rate was only 55% of that of trees irrigated with fresh water. Irrigation with saline water (EC = 7.5 dS m−1) reduced drought impact by increasing photosynthesis by 55% but remained lower than that of fresh water by 23%. Thus olive leaves were unable to recover their whole photosynthetic capacity after being exposed to severe water or salt stress. Furthermore, young leaves had the same photosynthetic capacity at the beginning. This indicated that olive leaves lost permanently half of their photosynthetic activity during to drought without irrigation. The use of saline water reduced this gap to 23% as compared to fresh water.

Water scarcity and the increasing water demand for irrigation in olive orchards are leading to adopt deficit irrigation approaches and the use of saline water. Field experiment was conducted on nine-year-old olive trees ( Olea europaea L. cv. Chemlali) grown on sandy deep soil and drip irrigated with saline water (EC 6.7 ms cm −1 ) under arid Mediterranean climate in southern Tunisia during 2003–2006. Three irrigation treatments (i) Control: full irrigated, (ii) DRY: rain-fed and (iii) PRD: partial root-zone drying were applied. PRD 30 and PRD 15 supplied 50% of the Control with an alternate irrigation switched every 30 and 15 days, respectively. PRD achieved significantly better soil water status in comparison to DRY and less than 30% of soil moisture level under the Control. Soil salinity levels were significantly lower during wet season than that of the summer period. PRD reduced the quantity of salt incorporated in the root-zone. Predawn ( Ψ PD ) and stem ( Ψ stem ) water potentials across all irrigation treatments diverged progressively from one another throughout summer season. Minimum values of −0.9, −1.3, −1.2 and −1.3 MPa for Ψ PD and −2.2, −2.4, −2.4 and −2.9 MPa for Ψ stem were measured during the summer for the Control, PRD 30 , PRD 15 and DRY, respectively. PRD showed statistically comparable values of water potentials to the Control which seemed to prevent an excessive drop in tree water status by modulating stomatal closure. High correlations of Ψ stem with Ψ PD and soil water potential indicated that Ψ stem could be used for the control of water supply in olive orchards. An improvement of olive yield was achieved by irrigation with saline water. PRD 30 achieved a slight cumulative yield reduction (11%) compared to the Control while applying half of irrigation quantity. The oil content showed an improvement with increasing deficits. PRD 30 seems to realize a good compromise between yield, quality and environmental impact and could be recommended for irrigation of olive trees under similar situations of water quality, soil and precipitation regimes.