Please see the specific soil water terms listed below and Table 5:

• soil water potential, (pressure, head) - The amount of work that must be done per unit of a specified quantity of pure water in order to transport reversibly and isothermally an infinitesimal quantity of water from a specified source to a specified destination. If the specified quantity is volume, the potential is referred to as pressure (Pa). If the specified quantity is weight, the potential is referred to as head (m). If the specified quantity is mass, the potential is the term used (J kg-1).
• hydraulic head, pressure, potential - The sum of gravitational, hydrostatic, and matric water potential, expressed as head, pressure, or potential.
• differential water capacity - The absolute value of the rate of change of water content with soil water pressure. The water capacity at a given water content will depend on the particular desorption or adsorption curve employed. Distinction should be made between volumetric and specific water capacity.
• water content - The water lost from the soil upon drying to constant mass at 105 °C; expressed either as the mass of water per unit mass of dry soil or as the volume of water per unit bulk volume of soil.