Permanent wilting point
Permanent wilting point (PWP) or wilting point (WP) is defined as the minimal point of
soil moisturethe plant requires not to wilt. If moisture decreases to this or any lower point a plant wilts and can no longer recover its turgidity when placed in a saturated atmosphere for 12 hours. The physical definition of the wilting point (symbolically expressed as θpwp or θwp) is defined as the water contentat −1500 J/kg (or −15 bars) of suction pressure, or negative hydraulic head.
However, it is noted that the PWP values under field conditions are not constant for any given soil, but are determined by the integrated effects of plant, soil and atmospheric conditions.
The concept was introduced in the early 1910s.
Lyman Briggsand Homer LeRoy Shantz (1912) proposed the wilting coefficient, which is defined as "the percentage water content of a soil when the plants growing in that soil are first reduced to a wilted condition from which they cannot recover in approximately saturated atmosphere without the addition of water to the soil" (Taiz and Zeige, 1991). See pedotransfer functionfor wilting coefficient by Briggs.
Frank Veihmeyer and Arthur Hendrickson from University of California-Davis found that it is a constant (characteristic) of the soil and is independent of environmental conditions.
Lorenzo A. Richardsproposed it is taken as the water content at −1500 J/kg. [cite journal|author=Veihmeyer, F.J. and Hendrickson, A.H. |year=1928|title=Soil moisture at permanent wilting of plants |journal=Plant Physiol. |volume=3 |pages=355–357 ]
Available water capacity
Nonlimiting water range
Soil plant atmosphere continuum
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