THE USE OF THE EVAPOTRANSPIRATION STRESS INDEX (ETSI) TO GUIDE IRRIGATION MANAGEMENT IN YOUNG OLIVES

Early detection of plant water stress in any crop planted for commercial reasons is an advantage when trying to match limited water resources with optimum crop yield and health. Daily water use of young olive trees (Olea europaea ‘Frantoio’) was measured on a near-continuous basis (10-min intervals) for a full year using Sentek^® capacitance sensors. Basic growth indices were also taken on selected trees. A new measure called the Evapotranspiration Stress Index (ETSI) to aid in the early detection of plant water stress is proposed. Using site-specific calibrated soil pore water values, it was possible to derive accurate estimates for the Volumetric Water Content (VWC) independent of soil texture. Independently collected and calculated potential evapotranspiration (ET_o) values were obtained from a nearby government (Bureau of Meteorology) weather station. The ratio of the observed evapotranspiration and the daily water use as recorded on the Sentek sensors gave a numerical value of ETSI. This was aligned graphically with established concepts of stress indicators developed by Sentek^® to more clearly indicate where plants were experiencing significant water stress. It was also possible to determine plant water stress thresholds using this index, giving clear indications as to where intervention by the irrigation operator was required in future. The increasing use of weather stations and soil water monitoring equipment by horticultural operators has driven the need for simpler data integration and clearer indicators for when irrigation is required. The development of ETSI as an additional tool for growers fulfils this need.