1. Chapter 5
5.2 Soils

2. Characteristics of Soil
Soil is part of regolith (loose materials that cover Earth) that supports the growth of plants
There are three important characteristics to soil
Composition
Texture
Structure

3. Characteristics of Soil- Composition
Soil has four major components:
Organic matter, or humus, which is the decayed remains of organisms
Mineral matter, or broken-down rock
Water (in pore spaces)
Air(in pore spaces)

4. Characteristics of Soil- Composition
In pore spaces between soil
particles is air and water

5. Characteristics of Soil Organic Matter
Organic matter is an important source of:
plant nutrients
and increases soil’s ability to hold water

6. Characteristics of Soil Mineral Part
Soil Texture – refers to the proportions of the 3 different particle sizes:
1. Sand (large size)
2. Silt (medium size)
3. Clay (small size)

7. Soil Texture
What type of soil consists of 10% clay, 60% silt, and 30% sand?
Silty Loam
Loam soil is the best for growing plants. Why?
A loam soil contains equal parts sand, silt, and clay

8. Soil Formation Time Climate
The longer the soil has been forming, the thicker it becomes
Climate
Greatest effect on soil formation
Variations in temp and precipitation influence the rate, depth, & type of weathering

9. Soil Formation Organisms
Plants are the main source of organic matter in soil
Microorganisms, including fungi, bacteria, and single-celled protozoans, play an active role in decomposing dead plants and animals
Burrowing animals mix the mineral and organic matter in soil

10. Soil Formation Slope On steep slopes, erosion is accelerated
Little water can soak in, so the soil generally holds too little moisture for plant growth
As a result, soils are usually ______ or __________.
thin
nonexistent

11. Soil Formation
Flat areas often have very thick soil

12. The Soil Profile Soil horizons are zones or layers of soil
A soil profile is a vertical
section through all the
soil horizons

13. Soil Profile

14. Soil Profile 1. A horizon Commonly known as “topsoil” 2. B horizon
Its upper part is made mostly of loose leaves and dead plants
2. B horizon
Commonly known as “subsoil”
Contains fine clay particles

15. Soil Profile
C Horizon
Contains partially weathered parent material

16. What is Soil Erosion?
Movement of topsoil down slope by the force of running water
Erosion can also be caused by blowing of soil particles by wind, like on a beach

17. Soil Erosion
Humans accelerate erosion by removing natural vegetation from land:
Examples –
1. farming
2. logging
3. construction
logging
construction

18. Decreasing Soil Erosion
Hillside Terracing

19. Decreasing Soil Erosion
Plowing along the contours of a hillside

20. Decreasing Soil Erosion
Planting rows of trees called windbreaks