When plants have removed all of the available water from a given soil, they wilt and do not recover. Thus, the water available for plant growth exists between the range of field capacity and wilting point. Available water capacity is all the water that a soil can possibly hold between field capacity and wilting point. The capacity varies with soil texture. Unavailable water is soil water held so firmly to soil particles by adsorptive soil forces that it cannot be extracted by plants.
Unavailable water remains when soil is direr than wilting point.
Volumetric water content is the total amount of water that a soil holds at a particular time. It includes the available, unavailable, and gravitational water, if present. Volumetric water content is the fraction or percent of water in the total soil volume. When water infiltrates into the soil from rain or irrigation, the pore spaces are nearly filled with water. During and immediately after a rain or irrigation the greatest movement of water occurs in the soil.