The total potential of water in a soil is the amount of work required per unit quantity of water to move a very small amount of water reversibly and isothermally from a pool of pure water at atmospheric pressure and at a reference level to the point of interest in the soil . This is the sum of the matric potential and the gravitational potential. The matric potential of water in a soil is the amount of work work required per unit quantity of water to move a very small amount of water reversibly and isothermally to the point of interest in the soil from a pool of pure water at atmospheric pressure at the same elevation . This is the amount of work required to move water into a soil from outside of it. Since the elevations are the same, gravity has no impact upon matric potential.
Matric potential is another term for pressure potential or pressure head.
This is simply the amount of work required to lift or lower the water from the reference level. The final units of potential depends upon the unit quantity of water chosen. It is convenient to define potential per unit weight. This means that all types of potential have units of length. So we commonly talk of total head, gravitational head, and pressure head or matric head.