Approach using trunk growth rate data to identify water stress conditions in olive trees

Abstract

Reduced water availability around the world drives the need for indicators that enable a better control of water stress at orchard level. Among the different parameters that could be used as indicators, trunk diameter fluctiations, are daily cycles suggested as tools for irrigation scheduling. These cycles can define different indicators and the trunk growth rate (TGR) was suggested as the most suitable for olive trees. Several works indicated that average TGR values are related to the tree water status even threshold values have been suggested. In addition, only daily TGR values below −0.1 mm day−1 were mentioned as water stress indicators. The aim of this work is to evaluate an irrigation scheduling approach based on those two results mentioned. To this end, an experiment was performed during the 2017 season, in a commercial, super-high-density orchard in Carmona (Seville, Spain). Four different irrigation treatments were applied based on midday stem water potential values and TGR. The Control treatment, with 100% ETc (crop evapotranspiration) and sustained deficit irrigation, was compared with two regulated deficit irrigation strategies based on TGR measurements. Severe water stress conditions were measured in the three deficit treatments. Irrigation scheduling using average TGR was not a suitable tool for the aim of the experiment because some data were lost and there were great variations in TGR values. However, it was found that average TGR values were related to midday stem water potential. The water potential and daily TGR data were grouped according to water stress levels (into values with water potential higher of −1.4 MPa and lower than −4 MPa). Daily TGR values greater than 0.3 mm day−1 were identified in response to severe water stress conditions. Weekly frequency of daily TGR values between −0.1 and 0.3 mm day−1 decreased from 60% to 25% when water stress level increased. Therefore, frequency and value of daily TGR are suggested as irrigation scheduling tools for olive trees.