Download Soil Texture

Soils & Soil FormationThe Results of
Weathering
Regolith
A layer of weathered
rock fragments
covers much of the
Earth’s surface

Regolith
Soil
part of the regolith that
supports plant growth
Complex mixture of
minerals, water, gases,
and remains of plants and
animals

What is Soil Composition?

has 4 major components:
•mineral matter
•organic matter (humas)
•water
•air
Composition of Soil:
What is Humus?
Dark, organic material,
remains of animals and
plants

Humus:

•
What are the Soil
Textures?
Texture refers to the proportions
of different particle sizes.
- Sand (large size)
- Silt
- Clay (small size)
•
Loam (a mixture of all three sizes) is
best suited for plant life.
CLAY
SILT
SAND
Soil Texture
What are the most important
factors in soil formation?
(1) parent material
•source of the mineral
matter in soil
Residual soil—parent material is the
bedrock below the soil
• Transported soil—has been
carried from parent material and
deposited elsewhere
•
(2) Time
•
•
Important in all geologic processes
The longer a soil has been forming,
the thicker it becomes.
(3) Climate
• Greatest effect on soil formation
(4) Organisms
• Organisms influence the soil's
physical and chemical properties.
• Furnish organic matter to soil
(5) Slope
•Steep slopes often have poorly developed
soils.
• Direction the slope is facing influences soil
formation (affects soil temperature and
moisture)
Thinner on slope
because water erodes
soil & deposits it down
the slope
Tends to be
thicker here
(deposited)
What is a Soil profile?
A cross-section in which the
layers of the soil and
bedrock can be seen
 Each layer is called a horizon.
 In fully developed residual
soil, there are three horizons

A horizon
(topsoil)

mixture of organic matter
and small rock particles
B horizon
(subsoil)
•contains minerals and clay
C horizon
(regolith)
partially
weathered
bedrock

Bedrock
Solid, unweathered
rock that lies beneath
regolith

Bedrock
What role does Climate play
in soil formation?

Climate is most
important factor
influencing soil
formation
What is a Temperate climate?
Temperatures range from
cool to warm
Rain fall is not excessive
Two types of soil are
found dependent on
amount of rainfall:

What are the soil types of
temperate climates?
1.
Pedalfer – soil formed if an area
receives 65 cm or more of rain per
year (clay, quartz, iron)
-found in eastern United States
2. Pedocal – soil formed if rainfall is
less then 65 cm a year (calcium
carbonate)
-found in western United States
Pedalfer
Pedocal
What is the soil formation
in tropic areas?

forms laterites (thick and
infertile soil)
*rain always is washing
away the A horizon but
constant rotting
vegetation covers the B
Horizon
Laterite
What is soil formation of a
desert?
Forms soils from
mechanical weathering
Soil is thin and mostly
of regolith
