Soil Formation 6.E.2.3
Soil is a mixture of
rocks, minerals, decayed
material, water, and air.
Soil is one of Earth’s most valuable natural
resources.
Everything that lives on the land, including
humans depends on soil.
humus:
- Material that forms when plants
and animals decay.
- dark, organic
- makes space for air and water
- contains minerals needed by plants
- Decomposers help make humus.
Earthworms and burrowing
animals such as moles mix
humus and air into soil.
loam:
- rich fertile soil made of clay, sand, and silt.
bedrock (parent rock):
- solid layer of rock under soil.
Wherever bedrock is exposed, soil is always
being formed.
Why? Soil forms as rock is broken down by
weathering.
Horizon:
- layer of soil that is a
different color or texture.
Soil forms in layers called horizons.
O horizon: organic layer where plants grow.
A horizon: topsoil: humus and
tiny rock pieces
B horizon: subsoil: middle soil
layer, mostly clay
C horizon: bedrock (parent rock):
partly weathered rocks
fertility:
- measure of how well soil supports plant growth
- measured from high ------ low
- Soil loses its fertility when
topsoil is washed away
(erosion).
- When soil is bare, water and
wind carry soil away, plant
roots hold soil together and
STOP erosion.
Dust Bowl - during 1950’s on Great Plains
of U.S.
- Farmers in Oklahoma plowed up grass to
plant crops.
- Dry weather killed the crops which turned
the bare soil to dust.
- Wind blew the dust creating the Dust Bowl.
Less than ⅛ of Earth’s soil is good
for farming.
Soil can lose fertility if farmers continuously grow just one kind of plant
in the same field year after year.
crop rotation- rotating crops to a different field
each year to keep soil fertile.
contour plowing- plowing
in curves on a slope to prevent
soil loss.
contour plowing
Soil Conservation:
- using soil in ways to save it, stop erosion and
keep it fertile