The amount of water in a crop root zone that can be easily extracted by the crop. RAW is the fraction of the difference between FC and PWP that crops can use such that no stress caused by a lack of water occurs. Although crops can theoretically use all the water between FC and PWP, as PWP is approached the water becomes harder to extract and water stress and yield reductions will occur. Therefore, irrigations are scheduled when a fraction of the difference is used. The volume that the crop is "allowed" to use prior to another irrigation is RAW. RAW is expressed as a volume of water per unit of irrigated area, or as a depth of water per unit area in the same units as rainfall.