1. Soil
It’s not just DIRT

2. Why is soil important?
Soil is a natural resource. A natural resource is a material on Earth that is necessary or useful for people. It is not man made.
Because it is made from the weathering of rocks, it is considered a “renewable” resource.
Without soil, plants could not grow, which means people and animals would have no food!

3. How is soil formed?
It is the main product of mechanical and chemical weathering
Bacteria breakdown of plants and animals forming HUMUS
Worms, ants, moles, burrow through soil allowing water to weather rock and supplying nutrients.

5. What controls soil formation?
Parent material/Bedrock
Time: the more time soil has to develop, the thicker the soil, the less is resembles the parent material.
Climate: most influential factor
Plants and Animals: fertility depends on amount of organic matter
Slope:
Steep slopes: poorly developed

6. Topography

7. What makes up a Soil profile?
A soil profile is a vertical sequence of soil layers
A soil profile is made up of horizons. The number of horizons depends on how “mature” the soil is. “Mature” soils take 1000’s of years to form and contain about 6 horizons. “Immature” soils sometimes only contain 2 horizons.

8. How are soil profiles formed?

9. What makes up a soil profile?

11. What makes up each of the soil horizons?
The “O” Horizon: Topsoil, mostly plant litter at the top and humus at the bottom. Rich in organic material. Brown in color.
The “A” Horizon: Topsoil, dark in color, some humus, and biological activity
The “E” Horizon: Light colored mineral material
Leaching: Water percolates down and carries minerals down to lower horizons.

12. What makes up each of the soil horizons continued
The “B” horizon: Subsoil, contains clay material. Red-brown color.
The “C” horizon: partially altered parent material
Regolith: rock and mineral fragments, NO organic material
Residual soil: soil formed over the original bedrock. Resembles the bedrock/parent rock.
The “R” horizon: Solid bedrock/parent rock, unweathered

13. How are soils different?
Different soils are found in different places. Some soil is good for growing plants, while other soil is not.
Soils differ in color and texture. A soil’s color has to do with what’s in it. For example, red soil may contain a lot of iron. Dark brown or black soil contains a lot of humus.

14. Chemistry and Composition
Soil Types
Climate/Soil Type
Vegetation
Typical Area (s)
Common colors
Chemistry and Composition
Annual Rainfall
Fertility

15. What are the different soil textures?
Soil texture describes how big the particles, or pieces, of soil are.
Most soils are either sand, clay, silt, or loam.

16. Comparing Soil Layers

18. What are the different soil textures?
Sand: the largest particle in the soil. Water flows through it very easily. Because it doesn’t retain water very well, plants have trouble growing in this type of soil.
Clay is the smallest of particles. Clay also can hold a lot of nutrients, but doesn't let air and water through it well. Can result in TOO MUCH WATER for the plant.

19. What are the different soil textures?
Silt is a soil particle whose size is between sand and clay. Smaller than sand, larger than clay.
Loam: This soil is a mixture of sand, silt, clay and humus.
It is considered to be the perfect soil.
Holds water well and has many nutrients.

20. What is the difference between porosity and permeability?
Porosity is a measure of how much of a rock is open space. This space can be between grains or within cracks or cavities of the rock. Permeability is a measure of the ease with which a fluid (water in this case) can move through a porous rock.

21. The soil texture triangle
Soil texture depends on its composition and the relative portions of clay, sand, and silt. 

22. How to read the soil triangle
Classify a soil sample that is 30% clay, 15% silt, and 55% sand.

23. Now you try!
 60% clay, 20% silt, 20% sand

24. Now you try
Clay: 30% Sand: 30% Silt: ?

25. How is soil eroded?
Soil is eroded when it is moved from place to place
It is more common on steep slopes or where there is little vegetation
Balance is maintained when new soil forms at the same rate it is eroded

26. Wind erosion

27. Raindrop erosion

28. Vegetation protects soil

29. How do humans cause erosion ?
Agricultural practices such as plowing and slash and burn removes plant cover
Clear cutting for lumber, farming, and grazing
Overgrazing by sheep and cattle
Urban construction
Open strip mining

30. What can we do to slow the rate of soil erosion?
No-till farming is done without plowing leaving topsoil in place
Contour and Terracing uses the natural shape and slope of the land to grow crops
Rotation system