. We evaluated the effect of the four treatments on canopy volume (CV) during two growing seasons. For 28 days during the second growing season, we evaluated soil moisture content (θ), the soil-moisture depletion factor (p), trunk cumulative growth (TCG), trunk growth rate (TGR) and maximum daily trunk shrinkage (MDS). We found relationships between CV and TCG and between CV and TGR. There were no differences in MDS among the irrigation treatments. We observed significant water stress in plants in the 0.3 ETc treatment (p = 0.47). The highest growth was observed in plants in the 1.3 ETc treatment, which suggests that the crop coefficient (Kc) was underestimated.

Diameter fluctuations of branches, shoots, or fruits are related to plant transpiration and water potential. In the past, several models have related dendrometric variables and evapotranspiration on a daily scale. However, trunk–branch shrinkage occurs only between dawn and midday, while evapotranspiration occurs most of the day from sunrise to sunset. Previous models have failed to incorporate this key fact. The objective of the present study was to assess the relationship of hourly daily shrinkage (HDS) between dawn and the next 4 h to the hourly reference evapotranspiration (EToh) of the same period in walnut trees and pomegranate plants under different irrigation regimes. Our data show that the relationship between EToh and HDS is much better than several previous models that included maximum daily shrinkage (MDS) and reference evapotranspiration (ETo). The novel slope analysis of the relationship between HDS versus time used here corresponds to the velocity at which the HDS occurs, which depends on the ETo intensity at that moment. This new method of analyzing this type of data calls for a revision of these models and sets a new baseline for future analysis.