Water relations and yield of olive tree (cv. Chemlali) in response to partial root-zone drying (PRD) irrigation technique and salinity under arid climate

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 6.7mscm−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. PRD30 and PRD15 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 (ΨPD) and stem (Ψstem) water potentials across all irrigation treatments diverged progressively from one another throughout summer season. Minimum values of −0.9, −1.3, −1.2 and −1.3MPa for ΨPD and −2.2, −2.4, −2.4 and −2.9MPa for Ψstem were measured during the summer for the Control, PRD30, PRD15 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 Ψstem with ΨPD and soil water potential indicated that Ψstem could be used for the control of water supply in olive orchards. An improvement of olive yield was achieved by irrigation with saline water. PRD30 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. PRD30 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.