The timing of irrigation modifies the sensitivity to water stress of plant water indices derived from trunk diameter fluctuation in extra early nectarine trees

The sensitivity to water stress of different plant-based water status indicators was evaluated considering the timing of irrigation during a 4-year study in an extraearly nectarine cultivar. Two irrigation treatments were established: A control (CTL), irrigated to ensure non-limiting water conditions (120% of crop evapotranspiration) and deficit irrigation (DI) which involved 45% less water than CTL during postharvest. The plant water status indicators studied were: midday stem water potential (¿stem), maximum daily shrinkage (MDS) and two new indices derived from trunk diameter fluctuation or TDF (early daily shrinkage - EDS and late daily shrinkage - LDS). As expected, ¿stem showed the highest sensitivity at all times. EDS and MDS also showed high sensitivity when irrigation was applied only at night. The signal intensity (SI) of EDS was slightly greater than that of ¿stem. EDS was more sensitive than MDS, with higher SI and similar variability. However, MDS and EDS showed reduced sensitivity when two irrigations a day were applied. Although ¿stem detected water deficit, this is a discontinuous measurement which cannot be automated. Among TDF-derived indices, EDS was more sensitive than MDS and LDS.