New approach for olive trees irrigation scheduling using trunk diameter sensors

Trunk diameter fluctuations (TDFs) have been suggested as an irrigation-scheduling tool for several fruit trees, but the works in olive trees has not obtained successful results with any of the indicators (maximum daily shrinkage (MDS) and trunk growth rate (TGR)) that are calculated from the daily TDF curves. No studies of olive trees have ever used reference trees to reduce the influence of the environment, as in work for other fruit trees. In this work, we compare different continuous and discrete water status measurements in a drought cycle. We suggest the calculation of a new and related indicator (DTGR), the difference between the TGR of stressed trees, and the TGR of reference trees. Negative DTGR values always indicate water stress conditions. The current work describes the variations of this new indicator (DTGR) in relation to water stress, and compares DTRG to the midday stem water potential, maximum leaf conductance and to the MDS. The midday stem water potential and the maximum leaf conductance describe the stress cycle clearer than the trunk diameter fluctuation indicators. No significant differences were found in the values of MDS between stressed and reference trees. On the other hand, the DTGR pattern values were near that of the stem water potential, though positive values were recorded in some dates during the water stress cycle. These variations indicate that DTGR is not a cumulative water stress indicators, as is water potential. Therefore, according to our data, water potential is a better indicator than the TDF parameters when no deficit irrigation scheduling is performed in olive trees. DTGR seems to be a good indicator of water stress from a threshold value around −1.4 MPa in olive trees. In addition, higher variability of DTGR than stem water potential may also be reduced with the increase in the number of sensors.