Calculation of total and component potentials of water in Soil

The total potential of water in moist soil is assumed to be the sum of gravitational, pressure, osmotic and adsorption components. Osmotic potential is related to solute concentration at any point. Adsorption potential is assumed to depend on interaction of water dipoles with electric fields associated with the solid‐liquid interface. The Gouy‐Chapman theory of the electric double layer provides a basis for computing both osmotic and adsorption potentials at any point in the liquid outside the first few monolayers of water enveloping soil particles. From these, pressure potential can be calculated. Curves illustrating the variation of component potentials with distance from a particle are presented along with curves relating total potential to film thickness for soils brought to hydraulic equilibrium or to vapor equilibrium with external solutions. Measurement of total potential by freezing point depression is questioned.