Regulated deficit irrigation based on threshold values of trunk diameter fluctuation indicators in table olive trees

The aim of this study was to establish threshold TGR and MDS values which could be used in regulated deficit irrigation in future work. Three irrigation treatments were performed during three seasons in a 37 year-old table olive orchard in Seville (Spain). Control treatment was irrigated with 125% of the crop evapotranspiration. Regulated deficit irrigation (RDI) treatments were performed according to the phenological stage of the trees and different water stress levels. RDI trees were irrigated only when the threshold values of water stress level was reached. Water stress conditions were applied during the massive pit hardening period (phase II, RDI-2) or during this period and the shoot-flowering period (phase I, RDI-12). The water stress level was performed with the trunk growth rate (TGR) during phase I and recovery and maximum daily shrinkage signal (MDS signal) during phase II. Both parameters were calculated as relative values of the Control trees. TGR threshold values varied from equal to Control (RDI-2) or 0.25 μm day−1 less than Control (RDI-12) during phase I. MDS signal (ratio between MDS in RDI vs MDS Control) threshold values varied from 0.5 (RDI-12) to 0.75 (RDI-2). In the recovery period, trees were irrigated when TGR values were lower than Control. This scheduled changed the amount of applied water between high and low fruit load seasons. The total amount of applied water in RDI trees oscillated from 38 to 160 mm, depending on the season and the treatment. The yield was not significantly different between Control and deficit treatments. Fruit volume and number of fruits was affected for the irrigation. Limitations and management of TDF in irrigation scheduling is discussed.