Pressure measured in bars or kilopascals. As the moisture content of the soil decreases, the amount of force required to remove the remaining water increases. Capillarity Refers to the rise of water into soil pores from a water table. The water rises in response to the matric potential. Water will rise in the soil pores until the matric potential is equal to the pull of gravity.
Dissolved substances lower the free energy of water.
When a differentially permeable membrane such as a plant root is involved, energy in addition to matric potential must be used to move water. The gravitational potential is the amount of work that must be expended to move a given mass of water against the force of gravity. There is a continuous decrease in the matric potential as water films surrounding soil particles increase in thickness. When water films are only one molecule thick, water is held at about -10,000 bars. As films become thicker and thicker, the matric potential becomes smaller and smaller.