Submitted to: Encyclopedia of Water Science
Publication Type: Other
Publication Acceptance Date: 2/12/2002
Publication Date: 8/1/2003
Citation: TOLK, J.A. SOILS, PERMANENT WILTING POINTS. STEWART, B.A., HOWELL, T.A., EDITORS. MARCEL-DEKKER, INC., NEW YORK, NY. ENCYCLOPEDIA OF WATER SCIENCE. 2003. P. 927-929. Interpretive Summary: Permanent wilting point (PWP) is the lowest amount of water that remains in the soil because a plant is unable to extract it. Along with the upper boundary called field capacity, which is the amount of water in a wetted soil after it has drained, PWP establishes the size of the reservoir of water in a soil that can be used by plants to maintain life. Measurement of PWP is not easy, because PWP is determined by a complex combination of factors involving the plant, soil, and the atmosphere. This article describes various techniques for estimating PWP.
Technical Abstract: Permanent wilting point (PWP) defines the lower limit of water use by plants. It is a product of many factors, including water potential gradients between and within the soil and plant, rooting characteristics and distribution, and atmospheric demand. It has been estimated as the soil water content 1) at which the leaves of a sunflower (Helianthus annuus sL.) Grown in the soil remain permanently wilted even when placed in a humi environment, 2) remaining in a soil placed under 1.5 MPa pressure, and 3) in a field where plants were at or near premature death or became dormant. This article describes the procedures for estimating PWP.