Understanding Soil AndWater Relationships
MT. VERNON, ILL.
The 2008 crop season has
certainly started out as a
wet one. Excessive moisture
has delayed planting and
made field operations difficult
at best.
By mid-May, some areas in
southern Illinois had already
received as much rain as they
would in a dry year. Many areas had recorded
up to 70 to 80 percent of normal annual rainfall
by mid-May.
The characteristics and physical properties of
a soil influence the soil-water relationship. It is
often stated that an ideal soil composition is 50
percent mineral and organic matter in combination
with 25 percent air and 25 percent
water. Obviously, the water has been displacing
the air in our soils for most of this spring.
Quite a few southern Illinois soils have poor
internal drainage, and some also have poor surface
drainage. Much of this is dependent on soil
texture, structure and slope.
Texture is essentially the size and composition
of the particles that make up the soil. An example
of coarse soil might be large sand. An example
of a fine-particle soil would be clay. Silt
represents the medium-sized particles. A real
world soil is usually made up of a combination.
Why is this important? Sand drains quickly
but has low water-holding capacity. Clay holds
large amounts of water; however, it is quite slow
to release water. Medium-textured silt loam
soils are considered to have both good drainage
and good water-holding capacity.
Soil structure is defined as the arrangement
of soil particles into aggregates of different sizes
and shapes. The clusters of soil particles are
called peds. Structure does not change texture,
but a desirable structure can improve tilth as
well as air and water movement. A structure
that is granular to angular blocky is considered
desirable.
Additional soil characteristics such as moisture-
holding capacity, permeability,
porosity, water availability, depth, and bulk
density are also important. Soils are complex
and dynamic in that they continue to change.
Amount of slope and length of slope are field
characteristics rather than soil characteristics.
Slope does influence surface drainage capability
and erosion potential. Soil scientists classify
slope by gradient, complexity, length and aspect.
So now you know . . . it is not just a wet field;
it is an elaborate, blended, intricate, saturated
soil. Seriously, remember that soil is a valuable
life-sustaining resource. Improve your soil
through informed management decisions. Δ
Dennis R. Epplin is Extension Educator, Crop
Systems, with the University of Illinois at the Mt.
Vernon Extension Center.