1. Soils

2. We can’t live without it
All land life depends on it
There isn’t very much good soil available on Earth
Required to grow plants
All animal life on land depends on plants

3. What is soil?

5. Where does soil come from?
All soil starts from rock. Rock that has never been worn down is called bedrock.
Rock must weather (break down) into smaller and smaller pieces
Rock can break down in two ways.
Chemical weathering
Physical weathering

6. Chemical and Mechanical Weathering

7. Weathered Rock
Weathered rock doesn’t stay put, but is usually moved by erosion
Erosion can happen from
wind water ice

8. Erosion

9. Characteristics of Soil (how we can describe soils)
Color
Particle Size
Texture
Consistency pH
Moisture
Temperature

10. Soil Color Two sources of color in soils
Minerals in the soil: for example. red clay soils have a lot of iron; brown/black soils have manganese….different minerals have different colors
Mica is dark Quartz is light Hematite is red

11. Soil Color, continued
The more organic material, the darker the soil. Organic material comes from dead plants and animals. Organic material in soil is called humus.
Humus is THE most important factor in soil color. The more humus, the darker the soil.

12. Soil Particle Sizes
Sand—smaller than gravel, you can still see it, feels grainy, water flows through easily
Silt—smaller than sand, can’t see individual particles, feels smooth like powder, water has a harder time flowing through
Clay—smaller than silt, feels sticky, water usually doesn’t flow through

15. Consistency
Soil consistency means how the soil likes to stick together. It depends on the kinds of minerals in the soil and how much water is in the soil
Does it stick together when you squeeze a handful of it? Does it crumble apart? Is it sticky?

16. Soil pH pH is the way we measure how acid or basic something is
It usually ranges from 0 to is very acidic while 14 is very basic, 7 is neutral like pure water
Acids: lemon juice, orange juice, sodas
Bases: Clorox, ammonia, baking soda

17. Some plants like acidic soils

18. Other plants like basic soils
But if soil is too acid or basic, no plants can grow

19. What does the pH level do?
pH of the soil affects how minerals dissolve. The best pH for soils and plants is between 6-7, slightly acidic.
At this pH, the nutrients from minerals become available to plants. The water in the soil will dissolve the nutrients from the minerals in the soil! Happy plants!

20. Nutrients Nutrients are the chemicals that an organism needs to
grow or maintain
its life.

21. Soil moisture
Plants need moisture. If soil is too dry, plants won’t grow. If soil is too wet, plants won’t grow. Moisture must fall in a range for plants to grow.
too wet too dry

22. When soil becomes too dry, it can more easily erode in the wind.
An important example of this is the Dust Bowl from the 1930s. A drought in the plains states, along with poor farming practices, caused heavy erosion of topsoil.

23. Dust Bowl, cont. Dust bowl lasted 10 years!
It took place in the southern Plains States

24. Soil temperature If soil temperatures are too high or low,
plants can’t grow

25. Review of Good Soil
Dark in color means high nutrients, both organic (humus) and inorganic (mineral)
Not too dry or wet
Slightly acidic pH
Not too much sand or clay
Deep layer of topsoil

26. Soil Horizons

27. Horizon Horizon: a side profile of the layers of soil
Soil is usually divided into 3 main layers, but will also include the layers above and below for a total of 5 layers.

28. O Horizon: Litter Not really a layer of soil
It’s on top of the first layer of soil
Contains grass, plants, and animals

29. A Horizon: Topsoil 1st layer of soil
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

30. B Horizon: Subsoil 2nd layer of soil Lighter in color (reddish brown)
Fewer nutrients and water
Limited plant growth

31. C Horizon: Parent Material
3rd layer of soil
Lightest in color (gray)
No nutrients, animals, or plant growth
Contains weathered rock and sediment

32. R Horizon: Bedrock Below the last layer of soil Solid Rock
Has not been weathered or broken down yet
No soil in this layer

33. Soil Horizons Diagram Copy this into your notes O Horizon: LitterN
A Horizon: Topsoil
B Horizon: Subsoil
C Horizon:
Parent Material
R Horizon: Bedrock