Soils & Soil Formation-The 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?

• Loam (a mixture of all three sizes) is best suited for plant life.

• Texture refers to the proportions of different particle sizes. - Sand (large size)

- Silt- Clay (small size)

CLAY

SILT

SAND

Soil Texture

•source of the mineral matter in soil

What are the most important factors in soil formation?

(1) parent material

• Residual soil—parent material is the bedrock below the soil

• Transported soil—has been carried from parent material and deposited elsewhere

(2) Time

• The longer a soil has been forming, the thicker it becomes.

• Important in all geologic processes

(3) Climate• Greatest effect on soil formation

(4) Organisms

• Furnish organic matter to soil

• Organisms influence the soil's physical and chemical properties.

(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