1. Soils

2. Soils
Products of weathering

3. Soil Characteristics Regolith Loose material covering solid rock
Dust, sediment, broken rock
Soil is the only part that supports the growth of plants

4. Soil Characteristics
Composition
Texture
Structure

5. Soil Composition Mineral matter Organic matter (humus) Broken rocks
Remains of dead organisms
Source of nutrients
Increases ability to retain water
Percentage varies
Bogs are almost all humus, deserts have very little

6. Soil Composition Water Air Provides moisture for chemical reactions
Provides nutrients in a form that plants can use
Air
Source of CO2

7. Soil Texture The proportions of particle sizes
Influences ability to support plant life
Based on % of clay, sand and silt

8. Soils
SAND:
Drains quickly; dries out

9. Soils
LOAMY SAND:
falls apart when handled.

10. Soils LOAM: feels spongy Drains well without drying out
Contains more nutrients

11. Soils
SANDY LOAM:

12. Soils
SANDY CLAY:

13. Soils
SILT LOAM:

14. Soils
CLAY:
Drains slowly
Hard for plant roots to grow

15. Soils
SILTY CLAY:

16. Soils
SILTY CLAY LOAM:

17. Soils
CLAY LOAM:

18. Good Quality Soils
Typically consist of 50 % organic and mineral matter
Other 50 % consists of pore spaces
Air and water circulation

19. Soil Structure
Soil particles form clumps that give soils a particular structure
Determines:
How easily it will erode
How easily it can be cultivated
Water infiltration

20. Soil Formation

21. Parent Material Source of the mineral matter Bedrock
Residual soil
Unconsolidated material
Transported soil

22. Parent Material Affects: Rate of weathering and soil formation
Unconsolidated material forms soils more quickly than residual
Plant fertility
Determines types of plants that can grow

23. Soil Formation Climate: Time: Temperature, humidity, precipitation
Most important factor
Time:
Older soils are thicker

24. Soil Formation Organisms
When living things die, decomposers break them down
They become part of the soil
Add nutrients to soils
Plant acids speed up weathering
Burrowing
leaves holes for air and water circulation

26. Soil Formation Topography/Slope
Steeper slopes have more erosion, less water

28. Soil Profiles Soil forms top down At different depths, soil varies in:
Composition, texture, structure and color

29. Soil Profiles
Mature soils tend to have 3 distinct horizons

30. Soil Horizons O A B C Humus, typically considered part of A
Topsoil, mostly organic matter B
Subsoil, lower limit of roots and burrowing,
Hardpan – clay that forms a compact layer C
Partially weathered parent material

31. Pedalfer
Forms in temperate areas with more than 63 cm of rain each year
Much of the eastern US
B horizon
Large amts. of iron oxides (reddish brown)

32. Pedocal Forms in drier western US Less clay (b/c weathering is slower)
Contain calcium carbonate – light brown

33. Laterite Hot, humid, tropical areas Lots of water
Distinctive orange-red
Almost no organic material (quickly used)