1. Chapter 5
5.2 Soils

2. Characteristics of Soil
Soil is part of the 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:
Mineral matter, or broken-down rock
Organic matter, or humus, which is the decayed remains of organisms
Water
Air

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
Water also provides nutrients
Desert soils only contain a tiny amount of organic matter

6. Characteristics of Soil Mineral Part
Soil Texture – refers to the proportions of different particle sizes
Sand (large size)
Silt
Clay (small size)
Loam (a mixture of all three sizes) is best suited for plant life
Why is loam the best for plant growth?
Loam provides the best of all worlds… it doesn’t dry out fast but doesn’t retain too much water.

7. Soil Texture
What type of soil consists of 10% clay, 60% silt, and 30% sand?
Silty Loam

8. What type of Soil do we have?
Silt-60% Clay-20% Sand-20%
Silt-10% Clay-60% Sand-30%
Silt-33% Clay-33% Sand-34%
Silt-20% Clay-30% Sand-50%
¼ clay, 4/8 sand, 2/8 Silt
Make up three of your own and trade with a friend. Try to make it tricky!

9. Now it’s your turn!
Make up three of your own and trade with a friend. Try to make it tricky!

10. Soil Formation Parent Material – source of mineral matter Time Climate
The longer the soil has been forming, the thicker it becomes
Climate
Greatest effect on soil formation

11. Soil Formation Organisms Plants-main source of organic matter in soil
Microorganisms decompose dead plants and animals
Burrowing animals mix the mineral and organic matter in soil

12. 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

13. Soil Formation
Flat areas often have very thick soil

14. The Soil Profile A horizon Soil horizons - zones or layers of soil
Soil profile - vertical section
A horizon
topsoil
Upper part - mostly loose leaves and dead plants

15. Soil Profile B horizon C horizon fine clay
Between B and the unaltered parent material
partially weathered parent material

16. What is Soil Erosion?
Movement of topsoil down slope by the force of running water or wind

17. Soil Erosion Rates of Erosion
Humans accelerate erosion by removing natural vegetation from land:
Examples –
farming, logging, and 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