Permanent wilting point

The permanent wilting point ( PWP ) or wilting point indicates the degree of dryness of a soil. The term comes from plant ecology.

Dries a floor to the permanent wilting point, the water is so strongly tied in well-rooted soil horizon that plants irreversible ( irreversible) wilt.

The plant's roots can not develop comparably high suction pressure to take the water out of the ground at such a low soil moisture. In the pathways of the plant ( xylem ) of the capillary water flow breaks away from the roots to the leaves, it enters the air. As a result, the plant wilts.

The permanent wilting point is to be understood as a convention. There are drought-resistant plants, mainly xerophytes that can overcome much higher suctions. Moreover, not only the hydrostatic pressure crucial, but also the hydraulic conductivity of a soil for the withering of a plant.

When wilting point PWP all water-bearing coarse pores and meso pores, ie soil pores with an equivalent diameter of> 0.2 microns are dry. The permanent wilting point is at a pF value of the soil of 4.2. This corresponds to a soil water potential of -1.5 MPa or 150 m water column in relation to the water table.

The amount of water that can hold a soil available to plants between field capacity and permanent wilting point depends largely on the humus content and the grain size distribution in the soil. This relationship can be seen in the voltage curve of a water base. The water content at PWP provides a good comparison value for the clay content of a soil.

Central European climate conditions dry soils only in an uppermost layer of a few cm to the wilting point PWP from.

Permanent wilting point

See also