Soil moisture and vapour pressure deficit predict trunk water potential in field-grown kiwifruit

A dynamic model has been developed to predict trunk water potential (Ψtrunk) from soil water content (SWC) and air vapour pressure deficit (VPD) in field-grown kiwifruit. The model included a capacitor (trunk tissue) apart of soil in order to account for the time lag between transpiration and Ψtrunk. Sub-models were defined from known, calibrated or specifically developed relationships linking SWC or VPD to hydraulic resistances of the whole soil-leaf path and of the storage compartment, plant leaf area and transpiration. Estimation of soil water potential from SWC was also included. The estimations of Ψtrunk (Ψmodel) were compared with in vivo measurements via microtensiometers installed in vines under full irrigation or progressively droughted. The resulting Ψmodel values were closely related to actual ones showing a median R2 up to approx. 0.95. The model revealed that the daily water released by the compartment to the transpiration stream (up to 0.22 m³ ha⁻¹) makes the orchard almost entirely dependent on root water uptake, posing a significant challenge for irrigation management. The main advantage of the model proposed is the limited number (two) of operational inputs variables supporting the employment of a combination of model and sensors to enable easy, and relatively low-cost monitoring of plant water status and in turn irrigation management.