Soils & Soil Formation-The Results of Weathering

RegolithRegolith

A layer of weathered A layer of weathered rock fragmentsrock fragments

covers much of the covers much of the Earth’s surfaceEarth’s surface

RegolithRegolith

SoilSoilpart of the regolith that part of the regolith that supports plant growthsupports plant growth

Complex mixture of Complex mixture of minerals, water, gases, minerals, water, gases, and remains of plants and remains of plants and animalsand animals

What is Soil Composition?What is Soil Composition?

has 4 major has 4 major components:components:

•mineral mattermineral matter•organic matter (humas)organic matter (humas)•waterwater•airair

Composition of Soil:Composition of Soil:

What is Humus?What is Humus?

Dark, organic Dark, organic material, remains of material, remains of animals and plantsanimals and plants

Humus: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)

CLAYCLAY

SILTSILT

SANDSAND

Soil TextureSoil Texture

•source of the mineral source of the mineral matter in soilmatter in soil

What are the most important What are the most important factors in soil formation?factors in soil formation?

(1) parent material(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 profileWhat is a Soil profile??

A cross-section in which the A cross-section in which the layers of the soil and bedrock layers of the soil and bedrock can be seencan be seen

Each layer is called a Each layer is called a horizonhorizon..In fully developed residual In fully developed residual

soil, there are soil, there are three three horizonshorizons

A horizonA horizon(topsoil)(topsoil)

mixture of organic matter mixture of organic matter and small rock particlesand small rock particles

B horizon(subsoil)

•contains minerals and clay

C horizonC horizon(regolith)(regolith)

partially partially weathered weathered bedrockbedrock

BedrockBedrock

Solid, unweathered Solid, unweathered rock that lies beneath rock that lies beneath regolithregolith

BedrockBedrock

What role does Climate What role does Climate play in soil formation?play in soil formation?

ClimateClimate is most is most important factor important factor influencing soil influencing soil formationformation

What is a Temperate What is a Temperate climate?climate?

Temperatures range from Temperatures range from cool to warmcool to warm

Rain fall is not excessiveRain fall is not excessiveTwo types of soil are Two types of soil are found dependent on found dependent on amount of rainfall:amount of rainfall:

What are the soil types of What are the soil types of temperate climates?temperate climates?

1.1. PedalferPedalfer – soil formed if an area – soil formed if an area receives 65 cm or more of rain per receives 65 cm or more of rain per year (clay, quartz, iron)year (clay, quartz, iron)-found in eastern United States-found in eastern United States

2. Pedocal2. Pedocal – soil formed if rainfall is – soil formed if rainfall is less then 65 cm a year (calcium less then 65 cm a year (calcium carbonate)carbonate)-found in western United States-found in western United States

PedalferPedalfer

PedocalPedocal

What is the soil formation What is the soil formation in tropic areas?in tropic areas?

forms forms lateriteslaterites (thick and (thick and infertile soil)infertile soil)

*rain always is washing *rain always is washing away the A horizon but away the A horizon but constant rotting vegetation constant rotting vegetation covers the B Horizoncovers the B Horizon

LateriteLaterite

What is soil formation of a What is soil formation of a desert?desert?

Forms soils from Forms soils from mechanical mechanical weatheringweathering

Soil is thin and mostly Soil is thin and mostly of regolithof regolith