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2.1 Physical Characteristics
Soil Texture Class
Soil Texture Class
Soil texture class is a soil science classification. Soils are grouped into classifications
based on the percentages of sand, silt, and clay in the soil.
Glossary
For example, generally sandy soils promote
free water drainage and entry of air, and thus
they are prone to drought. Silty soils allow for
drainage, but not as fast as drainage through
sand particles. Due to the abundance of smaller
silt particles, silty soils often decrease the pore
space of the soil, causing drainage and aeration
issues. Soils high in clay have further effects on
water and nutrients. Clay particles hold water
tightly on their surface, as well as between
layers, and not all of the water that they hold
is available to plants. Clay particles are also
responsible for nutrient and water holding, due
to large surface area and surface area reactivity.
They can attract and hold minerals such as
calcium, magnesium, potassium, ammonium,
sodium, copper, aluminum, and hydrogen.
Note: Many of these properties are also
affected by the soil’s organic matter
component, which is discussed on page
24. Organic matter is different from the
mineral component, although organic matter
and mineral particles can be mixed together,
depending on where they are in the soil profile.
Instead of testing for the exact proportion of
silt, sand, and clay in every field or pasture,
we can get a lot of information by knowing
which class the soil is in, and this is information
that you will find on soil maps (see Chapter 3,
“Where to Sample” on page 84).
Some different combinations of soil particle distributions will have similar properties and can be
grouped together.
Soil texture classes are related to the degree of a soil’s:
•
Susceptibility to erosion
•
Aeration
•
Water flow in and out
•
Water holding capacity
•
Nutrient availability
•
Potential/suitability for crops