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2. Soil Fundamentals
Soil Forming Factors and the Soil Profile
Five soil forming factors:
Soils are formed through the weathering
of bedrock, which occurs via 1) climate
(principally temperature and precipitation)
and 2) the activity of living organisms, and
it is affected by 3) the length of time that
weathering has occurred. Soils develop
differently given 4) topography (for example
top of a ridge, on a slope, or at the bottom of
a drainage) and 5) the original composition
of the bedrock. Soil is a balance of material
accumulated, transformed, and removed over
space and time.
A hypothetical soil profile is shown on the
right. You may see these visibly different layers
in croplands, but we don’t commonly see a
cross section like this on the rangelands of New
Mexico and Colorado, where we are more likely
to see an arid soil profile, like the one shown
on the far right. Soils in this region are often
shallower, due to water-limited soil formation,
and will have no O horizon and a smaller A
horizon due to water-limited plant growth and
reduced accumulation of dead plant matter
on the surface. It is useful to understand the
soil profile of a ranch or farm to understand
what can be expected from the architecture
and behavior of its soil under management
practices. (For information on ways that
management affects the soil profile, see Soil
Management Considerations, page 97)
Bedrock
the solid rock formed by earth processes
that underlies the soil. Soil is formed when
weathering breaks down the solid bedrock.
Bedrock is often referred to as the soil “parent
material.”
Glossary
Hypothetical
Soil Profile
Transformations
Climate
Organisms
Topography
Time
Bedrock
Inputs
Outputs