1. Soil Formation Soil is an important natural resource
It is found almost everywhere on Earth
Exactly what is it?

2. Soil Formation
Soil
Loose covering of broken rock particles and decaying organic matter (humus) overlying the bedrock of Earth’s surface.
Decaying organic matter is the decomposition of vegetation and animal remains in varying stages.

3. Soil Formation
Soil is the result of chemical and mechanical weathering and biological activity over long periods of time.
The soil-forming process begins when weathering breaks solid bedrock into smaller and smaller pieces.

4. Soil Formation
Bacteria, fungi, and insects begin to live in the weathered materials.
More nutrients are added to the weathered materials by the death and decay of organisms .

5. Soil Composition
Soil forms in layers during the process of its development.
The parent rock is the solid bedrock from which weathered pieces of rock first break off.
The smallest pieces of weathered rock, along with living and dead organisms, remain in the very top layer.
Rainwater seeps through this top layer of materials, dissolves soluble minerals, and carries them into the lower layers of the soil.

6. Soil Composition
Residual soil is soil located above its parent bedrock.
Transported soil is soil that has been moved to a location away from its parent bedrock by agents of erosion, such as running water, wind, and glaciers.
The parent bedrock determines what kinds of minerals a soil contains.
The parent rock and climatic conditions of an area determine the length of time it takes for soil to form.

7. Soil Profiles What is a soil profile?
A vertical sequence of soil layers
A soil horizon is a distinct layer, or zone, within a soil profile.
There are three major soil horizons: A, B, and C.

8. Soil Horizons (O) Organic matter
(A) Top soil with high concentration of organic matter & humus
(B) Subsoil enriched with clay minerals (Fe & AL)
(C) Weathered parent rock

9. Topography
Topography is the surface features of a place or region (e.g. valleys, mountains, rivers, etc.)
The topography of a region affects the thickness of developing soil.
Soils on slopes tend to be thin, coarse, and infertile.
Soils formed in lower areas, such as in valleys, are thick and fertile.

10. Soil Types Polar Soils Form at high latitudes and high elevations
Located in Greenland, Canada, Antarctica
No distinct horizons, very shallow soil
Just below the soil the ground is permanently frozen-known as permafrost
Permafrost in Denali

11. Soil Types Temperate Soils Lots of variation
Support forests, grasslands, prairies
Amount of rainfall determines what grows in this type of soil
Grasslands-lots of humus-soil is rich and fertile
Forests-soil is less deep/less fertile, containing clays and iron oxides (Eastern US)
Prairies-dry soil-lots of grasses and bushes

12. Soil Types Desert Soils Very little precipitation High levels of salts
Limited vegetation
Little or no organic matter
Very thin topsoil (A horizon)
Light colored and coarse soil

13. Soil Types Tropical Soils High temperatures, heavy rainfall
Soil is intensely weathered, infertile
Source of ores (iron), but not great for growing plants

14. Soil Types

15. Soil Textures
Particles of soil are classified according to size as being clay, silt, or sand, with clay being the smallest and sand being the largest.
The relative proportions of these particle sizes determine a soil’s texture.
The texture of a soil affects its capacity to retain moisture and therefore its ability to support plant growth.

16. Properties of Sand, Silt, & Clay

17. Soil Textures
To determine the texture of a soil sample, find its percent for sand, silt, and clay.
The texture of the soil will be where all three lines intersect.

18. Soil Fertility A measure of how well a soil can support plant growth
Factors involved include:
Availability of nutrients/minerals
Precipitation
Topography
Acidity
Number of microorganisms present

19. Soil Color Factors that determine soil color include: Climate
Soil’s composition
Topsoil-usually dark (rich in humus)
Red/yellow soils-caused by iron minerals oxidizing
Yellow soils are often poorly drained, associated with environmental problems
Gray/bluish soils-poorly drained, constantly wet, lacking in oxygen