Water potential

The concept of soil water potential is central to the characterization of water flow in unsaturated soils, to water retention, to plant available soil water and to soil strength. The concept is rooted in thermodynamic theory and reflects the attraction of soil and water, equilibrium between the liquid and vapor phases of soil water, and how gravity, pressure and soluble solutes affect soil water energy state and its exchanges with the atmosphere and plants. We review the historical roots of the water potential concept and offer practical definitions of the various components that contribute to water potential. Advances in measurement methods offer new insights into the relative influences of water potential components on water flow and exchanges with plants and the atmosphere.