The effect of deficit irrigation on seasonal variations of plant water use in Olea europaea L.

A field experiment on olive trees (Olea europaea L.) was designed with the objective to search for an optimum irrigation scheduling by analyzing the possible effects of deficit irrigation. Treatments were: a non-irrigated control (rainfed) and three treatments that received seasonal water amount equivalent to 33 and 66% of crop evapotranspiration (ET_C) in the period August–September (respectively 33II and 66II), and 66% of (ET_C) from late May to early October (66I-II). Atmospheric evaporative demand and soil moisture conditions were regularly monitored. Irrigation effects on plant water relations were characterized throughout a growing season. Whole-plant water use, in deficit irrigated (66I-II) and rainfed olive trees, was determined using a xylem sap flow method (compensation heat-pulse technique). The magnitude of variations in water use and the seasonal dynamic of water relations varied among treatments, suggesting that olive trees were strongly responsive to both irrigation amount and time. Physiological parameters responded to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. All measurements of tree water status were highly correlated with one another. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the water balance technique. Deficit irrigation during the whole summer (66I-II) resulted in improved plant water relations with respect to other watering regimes; while, severe regulated deficit irrigation differentiated only slightly 33II treatment from rainfed plants. Nevertheless, regulated deficit irrigation of olive trees after pit hardening (66II) could be recommended, at least in soil, cultivar and environmental conditions of this study.