Water scarcity and the increasing water demand for irrigation in olive orchards are leading to adopt

deficit irrigation approaches to save water. The partial rootzone drying (PRD) irrigation technique has been proposed for woody crops as an agronomic practice to improve water productivity. This study was conducted to evaluate the effect of this irrigation strategy on water relations and transpiration of olive tree (cv. Cobrançosa) under climate conditions of the Northeast of Portugal, during the season of 2014. To irrigation treatments were used: control (FI), irrigated with 100% of the estimated crop evapotranspiration (ET) and PRD₅₀, irrigated with 50% of the control on one side switching every two weeks. Whole tree transpiration (T) was quantified by sap flow, that was monitored within the trunk of both the control (FI) and deficit irrigated (PRD₅₀) trees using the compensation heath-pulse technique. Foliage gas exchange and water potentials were determined throughout the experimental period. During summer, daily transpiration reached roughly 27 and 43 L d^-1 for PRD₅₀ and FI olive trees, respectively, with a clear reduction of 32% in PRD₅₀ olives trees. PRD₅₀ 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.