The Soil Profile & It’s Formation

Importance of Soil

The Soil Profile• Soil forms in layers known as horizons. Each

horizon has its own characteristics.Let’s model them!

Let’s Share and Compare!Horizon Cookie Cherrios Marshmallows Fruity

KrispiesChocolate Krispies

O

A

B

C

R

What are the Layers? What are the Layers?

O: Contains organic detritus such as leaves, twigs, needles, etc.

A: Mixture of minerals and humus

B: Nutrients are here, but little organic material. Usually clay.

C: Partially weathered rock

R: Parent Rock

E: Zone of leaching

Why Are There Layers?The main process involved in soil formation is weathering!

Physical:The breakdown of rocks that result from mechanical processes such as temperature changes, abrasion, or frost.

Chemical:The breakdown of rocks through a change in their chemical makeup. Occurs when minerals in a rock interact with water, oxygen, or acids.

Biological:The breakdown of rocks by living things. Ex: Plant roots grow into cracks in a rock and expand it.

Other ProcessesErosion and Deposition:Determines the thickness of the soil as it is moved and accumulated.

Leaching:The process of water carrying soluble substances or small particles through soil or rock.

Key in the formation of the B-horizon!

Above and Below Delicate BalanceLeaching is important for creating a balance of salts and nutrients in the soil.

Salts are a natural product of weathering. They can build up in the top of a soil and prevent plant growth.

Too much leaching can remove nutrients from the top layers, making it difficult for plants to grow.

Soil Types Vary Around the World Factors Influencing SoilParent Material & Organisms: Determines the composition of the soil.

Climate:Determines the rate of weathering and organic decomposition.

Topography:Determines drainage and thickness of soil. Ex: steep hills have shallower soils.

Time:Determines the maturity of a soil.

Dry, cold = slow Moist, warm = fast

Put These in Order from Most Fertile To Least!

1. Tropical Rainforest

2. Desert

3. Temperate Deciduous

A. 1, 2, 3

B. 3, 1, 2

C.3, 2, 1

D. 1, 3, 2

The abundance of rain causes leaching of nutrients in the rainforest!

http://www.soils4teachers.org/around-the-world

What’s the Order?• Which of the following puts the horizons in

order of formation?

1. C, B, A

2. A, B, C

3. C, A, B

4. B, C, A