Soil water potential per unit mass is expressed as

Soil water potential is defined as "the amount of work that must be done per unit quantity of pure water to transport reversibly and isothermally to the soil water at a considered point, an infinitesimal quantity of water from a reference pool.
Soil water potential is the sum of four different components: gravitational potential + the matric potential + the pressure potential + the osmotic potential.
Soil water potential per unit mass is expressed as L²T².