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Ch 03 SOIL
Section 6
E. SOIL: A RENEWABLE RESOURCE
1. Soil is a slowly renewed resource that provides
most of the nutrients needed for plant growth
and also helps purify water.
a) Soil formation begins when bedrock is broken
down by physical, chemical and biological
processes called weathering.
2. Mature soils, or soils that have developed
over a long time are arranged in a series of
horizontal layers called soil horizons.
Soil Formation
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ANIMATION
3. Soil horizons have distinct textures and
compositions these mature soils have at
least three parts
a) The top layer is the O horizon layer is
brown/black and composed of leaves, twigs,
crop wastes, animal waste, fungi and other
organic material
b) The topsoil layer is the A horizon which is
composed of decomposed organic matter
called humus which is teaming with bacteria
c) The B horizon (subsoil) and the C-horizon
(parent material) have most of the soil’s
inorganic matter—sand, silt, clay, and gravel.
Animation: Soil Profile
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ANIMATION
Layers in Mature Soils
4. Infiltration: the downward movement of
water through soil.
5. Leaching: dissolving of minerals and organic
matter in upper layers carrying them to
lower layers.
6. The soil type determines the degree of
infiltration and leaching.
Some Soil Properties
7. Soils vary in the size
of the particles they
contain, the amount
of space between
these particles, and
how rapidly water
flows through them.
Figure 3-25
Soil Texture
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ANIMATION