Transcript All About Soil - Mrs. Marshall's 6th Grade Earth Science

All About Soil
Soil Formation
 Soil
is formed from weathered rock
fragments, so the type of soil depends on
the parent rock (the source of the rock
fragments).
 If soil stays above the bedrock from which
it was formed, it is called residual soil. If it is
moved, it is called transported soil.
What is Soil?
 Soil
is the topmost layer of the Earth’s
Crust. It is a mixture of minerals, rock
particles, water, and organic material that
can support plant life.
Humus
 Humus
is the dark organic layer of topsoil
formed from decaying plant and animal
matter.
 Humus is important because it contains
nutrients and holds water.
Loam
 Loam
is a mixture of soil types (clay, silt,
and sand). It is good for growing plants
because it allow the correct amount of
water and air through.
Rate of Soil Formation
 Soil
formation is affected by the rate of
weathering in different climates. Some
influences include temperature and
moisture.

Example: Weathering occurs faster in hot
wet climates
Plants, Animals, & Soil
 Plants
leach nutrients from the soil.
Because of this, farmers must use cover
crops or crop rotation to return nutrients to
the soil.
 Animals that burrow in the soil cause
weathering as they upturn new rock
pieces. Some animals such as worms
return nutrients to the soil.
Soil Horizons
A Horizon
•
This is the topsoil
layer, and it
contains the
most humus. This
is the layers
where the most
leaching
occurs.
E Horizon
•
This is the eluviation
layer where there
most leaching of
nutrients occurs.
B Horizon
•
This is the subsoil
layer. Nutrients and
dissolved substances
from the top layers
are deposited here.
C Horizon
•
This is the layer of
parent material. It is
made up of partially
weathered bedrock.
R Horizon
•
This is bedrock.
There is little or no
weathering here.