Water transport in the soil‐root system: Transient analysis

Equations are developed which describe the transient flow of water in a cylindrical soil‐root system. The main objective is to calculate water potential distributions in the root cortex as well as in the surrounding soil. Numerical results indicate that there will be small water potential gradients in the soil relative to those in the root in the upper 90% of the water availability range. Contrary to past experiments, theory predicts that appreciable amounts of water should flow from roots to soil when roots well supplied with water are in contact with dry soil. An important implication of the study is that models designed to predict the pattern in which roots extract water from soil will have to consider the rate‐limiting aspect of the root tissue.