How does capillarity affect soil water holding capacity?
One important characteristic of soil is its ability to hold water against the force of gravity and supply a portion of that water to plants. Much of this capacity is related to the number and size of pores and channels distributed throughout a soil. Some water can be held so tightly on polar surfaces in the soil that many atmospheres of pressure are required to force this water out. Plant roots must out-compete the forces that hold water in soil to survive, especially as more and more water is removed from the soil. However, much of this water would not even be in the soil in the first place without capillarity. All rainfall would drain rapidly from the soil and not be available for long-term use by many organisms nor would it be available for plant root uptake days or weeks after rainfall events. Most of the water available for plants in soil is that water categorized as capillary water.
