Soil Formation and Layers

Soil Formation

What is the first step in soil formation?

The weathering of rocks

Mosses and lichens are called pioneer organisms because they are the first organisms to grow on rocks

What is the second step in soil formation?

the addition of humus (decaying organic matter)

• Complex mixture of minerals, water, air, organic matter, and countless organisms that are the decaying remains of once-living things.

• Forms at the surface of land

• Capable of supporting plant life and is vital to life on earth.

it is the “skin of the earth.”

What is soil?

​Humus

​O Horizon

A Horizon

B Horizon

​Top Soil

Subsoil

C Horizon

Parent Material

R Horizon

Bedrock

Organic

Soil Profile- Draw this!(SS)

A soil profile is a cross section of soil.

There are three major soil horizons – A, B, and C.

Drag and Drop

Put all of the soil horizons in the right order​ ​ ​ ​ ​

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Drag these tiles and drop them in the correct blank above

Humus

Horizon O

Horizon A

Horizon B

Horizon C

Horizon R

• Layer of soil with properties that differ from those above or below it.

  Soil Profile: specific location that can be different from place to place

• Soil is usually divided into 3 main layers (A, B, and C)

Soil Horizon

O is full of living thing:

plants, microorganisms

O Horizon

Characteristics

• Litter (trash, grass..)

• Dark brown

• Reddish brown(clay)

• Grayish brown

• Contains

  • weathered rocks

  • Solid rock

​It’s on top of the first layer of soil. Contains grass, plants, and animals

• Darkest layer of soil (dark brown or black)

• Contains humus, plant roots, small animals, water, and nutrients for plant growth

• The darker the soil, the more nutrients it contains

A Horizon

Topsoil 1st layer of soil

Horizon A

top & darkest layer (high concentration of organic matter - humus)

Top soil

• Lighter in color (reddish brown)

• Fewer nutrients and water

• Limited plant growth

​Some text here about the topic of discussion.

B Horizon:

2nd layer of soil

Horizon B

subsoil enriched with clay minerals leached from the topsoil.

• 3rd layer of soil

• Lightest in color (gray)

• No nutrients, animals, or plant growth

• Contains weathered rock and sediment

C Horizon:

Parent Material

Horizon C

bottom layer (weathered rock)

Parent Rock

Below the last layer of soil

• Solid Rock

• Has not been weathered or broken down yet

• No soil in this layer

R Horizon: Bedrock

Soil Textures

Particles of soil are classified by size.

The particles of soil are clay, silt, & sand.

What determines a soil’s texture?

The relative proportions of these particles.

The texture of a soil affects its capacity to absorb and retain water & support plant growth.

Soil Texture Triangle

Open Ended

How does soil quality affect humans?

How does soil quality affect humans?

Soil that is healthy (horizon A) is essential to the survival of humans. Farmers can’t produce crops for our food supply and producers (plants) are essential for all living things in the food web and of course they also provide oxygen.

Multiple Choice

What does the size of the soil particles determine?

• pH

• mineral composition

• texture

• horizon posiition

Multiple Choice

What are loam, clay loam, silt loam, and clay?

• Soil particle sizes

• Soil Textures

• Soil pH

• Soil composition