Permanent Wilting Percentage (PWP)
It is the percentage of moisture in the soil at which a plant wilts and does not recover unless water is added to the soil. PWP for clay is about 26%, for silt 10% and for sand 3-5%. It must be noted that PWP is used to express property of a soil not any feature of the plant. However, the moisture content at which any plant shows permanent wilting need not be the same for all plants even in the same soil. This happens because some plants are prone to wilting at fairly reasonable water content of soil while others wilt only when the moisture content is very much reduced.
The water status of a plant in terms of FC and PWP is significant only if the soil properties are known. This is because the soil determines the availability of water. However, it is desirable as well as easier to express soil water status in terms of water potential so that soils become uniform with respect to water.