Full Product Manual

Table Of Contents
Saturation
Field
Capacity
Permanent
Wilting Point
Gravitational Water
(Rapid drainage)
Capillary Water
(Slow drainage)
Available Water
(AW)
Hygroscopic Water
(Essentially no drainage)
Readily
Available
Water
Figure 3-2: Soil, water, plant relationships
Page 12 Chapter 3
Figure 3-2 shows the availability of water in soil for use by plants. Moisture held
in soil is classified in three categories:
Hygroscopic water is water that is held too tightly in the soil to be used by
plants.
Capillary water is water that is held in the pore spaces of the soil and can be
used by plants.
Gravitational water drains rapidly from the soil and so is not readily avail-
able to be used by plants.
The Permanent Wilting Point represents the boundary between capillary water
(water that is available for plant use) and hygroscopic water (water that is
unavailable to plants because it is held so tightly by the soil). Since hygroscopic
water is not usable by plants, continuous soil moisture levels below the Perma-
nent Wilting Point will result in the death of the plants.
Field Capacity represents the boundary between gravitational water (water not
readily available to plants) and capillary water. It is the upper limit for soil
moisture that is usable by plants.
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