Water that is held on the outer coating of soil particles and is freely available to the plant. It is the water which is retained in a soil between its field capacity and permanent wilting point.
The capacity of soils to hold water available for use by most plants. It is commonly defined as the difference between the amount of soil water at field capacity and the amount at wilting point. It is commonly expressed as inches of water per inch of soil. The capacity, in inches, in a 60-inch profile or to a limiting layer is expressed as inches. 12 inches
the capacity of soils to hold water available for use by most plants, usually defined as water bewteen -33 kPa and -1500 kPal. In a 2 meter profile, or a more shallow limiting layer, the values are as following: Very low 0-3 in 0-7.5 cm Low 3-6 in 7.5-15 cm Moderate 6-9 in 15-23 cm High 9-12 in 23-30 cm Very high More than 12 in More than 30 cm
Loosely, the amount of water available for plants to use. Specifically, the volume of water released from soil between the time the soil is at field capacity (the maximum water held in soil against the pull of gravity) until the time it is at the wilting point (the amount of water held too tightly in soil for commonly grown crops to extract). Loamy soils and soils high in organic matter have the highest AWC. Soil Ecology Terms David Sylvia at Penn State University maintains a glossary of Soil Microbiology Terms that you may wish to consult.
The weight percentage of water which a soil can store in a form available to plants. It is equal to the moisture content at field capacity minus that at the wilting point.
Available water capacity (AWC) is defined as the range of available water that can be stored in soil and be available for growing crops (Richards and Wadleigh, 1952).