1. Soil Formation

2. What is soil?
Soil is the loose covering of broken rock particles and decaying organic matter, called humus, overlying the bedrock of Earth’s surface

3. Why is soil important? Essential for all life on Earth!
We are dependent upon plants, which grow in soil, for food and other basic needs (clothes, etc)
Benefits: oxygen from plants, meat from animals dependent on plants for food, filters out pollutants

4. What lives in soil? All kinds of animals; including: Moles
Earthworms (night crawlers)
Nemotode (Round worms)
Root fungus
Bacteria

5. How Soil Forms…
Starts when physical or chemical weathering occurs, breaking rock into smaller and smaller pieces
Organisms like bacteria and fungi live on the smaller pieces of rock
Over time, the organisms die, decay, and add organic material to the soil.

6. Soil Profile
During soil formation, soil develops layers. A soil profile is a vertical sequence of soil layers.
Poorly developed soils show little distinction between layers.

7. Soil Profile 5 major soil horizons: O, A, B, C, and D
Horizon O- this is the top layer, the “organic” layer, made up of dead plant matter
Horizon A- high concentrations of organic material and humus are found in the “top soil.”

8. Soil Profile
Horizon B- “subsoil layer” that is enriched with clay material
May be red or brown in color as a result of iron oxides
Accumulation of clay in B horizon can lead to the formation of hardpan, a very dense layer that may allow little to no water to pass through
Horizon A
Horizon B

9. Soil Profile Horizon C contains weathered parent material
This layer usually has lots of large rocks mixed in the soil deep underground
All horizons may not be present in a given soil
Horizon C

10. Soil Profile
Horizon R is solid parent bedrock and is the last layer of the soil horizons
Horizon R Bedrock Layer

11. Soil Texture There are three main types of soil texture: (1) sand
(2) silt
(3) clay

12. Sand Larger soil particles Sand does not hold nutrients well
Little plant growth (think deserts and beaches)

13. Silt
Medium sized particles
Very fertile
Holds lot of water

14. Clay Smaller sized particles Stick together well Inhibits root growth
Holds water well
Found mostly in piedmont

15. Soil Texture
Relative proportions of different sized particles (clay, silt, and sand) determine a soil’s texture
The texture of a soil affects its capacity to retain moisture and its ability to support plant growth
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16. Soil Fertility
Soil fertility is a measure of how well a soil can support the growth of plants
Factors that affect fertility include:
(1) availability of minerals and nutrients
(2) number of microorganisms present
(3) amount of precipitation available
(4) Topography
(5) Level of acidity