WATER IN THE SOIL
• The water content
and the rate of
water movement in
soils depend to a
large extent on soil
type and soil
structure.
• In sandy soils, the spaces between particles are
so large that water tends to drain from them and
remain only on the particle surfaces and at
interstices between particles.
• In clay soils, the channels are small enough that
water does not freely drain from them; it is held
more tightly
Field Capacity
• The moisture-holding capacity of soils
• Field capacity is the water content of a soil after it
has been saturated with water and excess water
has been allowed to drain away.
• Clay soils or soils with a high humus content have
a large field capacity.
• As a soil dries out, water
is first removed from the
center of the largest
spaces between particles.
• Because of adhesive
forces, water tends to
cling to the surfaces of
soil particles, so a large
surface area between soil
water and soil air
Water has a high surface tension that
develops
tends to minimize air–water
interfaces.
• As the water content of the soil decreases, the
water recedes into the interstices between soil
particles, and the air–water surface develops
curved air–water interfaces.
• The value of p in soil water can become quite
negative because the radius of curvature of air–
water surfaces may become very small in drying
soils.