Matric potential includes osmotic, adhesive, and capillary pressure.
Osmotic potential is significant in the presence of a membrane such as the plant root membrane and an induced salinity gradient. However, we are generally concerned about free drainage of water from soils and not the removal of water from soils by plants, so we will ignore osmotic potential for most lectures in this class. The capillary potential is the difference in pressure between water and air in soil pores. We described the relationship between matric potential and gravitational potential in the previous lecture. The relationship between soil-water content and matric potential has been described by several models and innumerable papers.