Estimation of an effective soil water potential at the root surface of transpiring plants

A simple method is described for estimating an average of ‘effective’ soil water potential at the root surface for transpiring plants. The method is based on measurements of leaf water potential and leaf conductance to water vapour in stressed plants and in well‐watered controls, and uses the simple Ohm's law analogue for water flow in the soil‐plant system. The technique is applied to data for field‐grown apple trees and to previously published data for wheat and cowpea.