Scheduling regulated deficit irrigation in olive using leaf turgor measurements: another twist for the method

Precision irrigation is technically demanding and expensive, limitation that can be alleviated with leaf turgor pressure sensors (ZIM probes, also known as Yara-water sensors) as one of the promising tools for both monitoring plant water status and irrigation scheduling. Although ZIM probes have shown to be useful to schedule a regulated deficit irrigation strategy in a commercial olive orchard, this irrigation approach presents limitations beyond a certain level of water stress (ca. Ψ_stem<-1.7 MPa), when sensor readings are apparently no longer related to leaf turgor, which makes the sensor useless for irrigation scheduling in certain periods of the olive growing cycle. Here, we present results of an experiment with two-year old olive (Olea europaea ‘Arbequina’) potted trees in which irrigation was withheld to achieve values of midday stem water potential (Ψ_stem) below -1.7 MPa. The trees were monitored continuously with both ZIM probes and leaf thickness sensors. The aim of this work was to assess the actual significance of the ZIM probe records at high levels of water stress to establish new indicators for irrigation scheduling in periods of severe drought. Our results confirm that the relationship between the indicators derived from ZIM probe readings and Ψ_stem, that were stablished to schedule the stablished regulated deficit irrigation strategy, hold for ‘Arbequina’ olive trees under different environmental conditions. In addition, our results showed an agreement between diel dynamics in ZIM probe records and leaf thickness measurements, suggesting that the ZIM probe could be useful for irrigation scheduling of trees under severe water stress.