1. Soil

2. Importance of Soil An important product of weathering
Covers most land surfaces
One of Earth’s most important resources

3. Characteristics of Soil
 Soil is part of the regolith that supports the growth of plants.
• Regolith is the layer of rock and mineral fragments that covers most of Earth’s land surface.

4. Soil Composition Soil has four major components:
Mineral Matter-broken down rock
Organic Matter-HUMUS-the decayed remains of organisms
Water
Provides the moisture for chemical reactions to occur that sustain life
Air
Source of Carbon Dioxide plants use to produce sugar during photosynthesis

5. Composition by Volume of Good Quality Soil

6. Characteristics of Soil
 Soil Texture
• 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.
Sandy soils may drain out and dry too quickly
Clay rich soils drain very slowly

7. Soil Texture

8. Soil Characteristics  Soil Structure
• Soil particles clump together to give a soil its structure.
Determines how quickly soil can be cultivated and how susceptible it is to erosion
Affects how easily water penetrates soil

9. Soil Formation The most important factors in soil formation are:
Parent material
Time
Climate
Organisms
Slope

10. Soil Formation Parent Material Time
Source of mineral matter
Residual Soil- parent material is the bedrock
Transported Soil- Parent material has been carried from elsewhere and deposited by gravity, water, wind, or ice
Influences on Soil
Affects the weathering and rate of soil formation
Affects Soil fertility (what kind of plants it can support)
Time
The longer a soil has been forming, the thicker it becomes
Parent material mostly determines characteristics of young soils
As time and weathering continues, the influence of parent material decreases

12. Soil Formation Organisms
Climate
Greatest effect on soil formation
Different temperatures and moisture affects rate, depth, and type of weather
In the same amount of time:
Hot, wet climate: thick layer of chemically weathered soil
Cold, dry climate: thin layer of mechanically weathered soil
Amt of Precipitation influences soil fertility; rate at which nutrients are removed from soil
Affects types of organisms that can live on and in the soil
Organisms
Type and how many affect soil’s physical and chemical properties
Plants are main type of organic matter in soil; contributes to soil fertility (remember humus)
Microorganisms decompose dead plants and animals
Burrowing animals mix the organic and mineral matter and help water and air penetrate into the soil

13. Soil Formation SLOPE: On steep slope Flat areas Optimum slope
Erosion is accelerated
Often have poorly developed soils because little water can soak in and cant hold moisture for plant growth
Flat areas
Little erosion and poor drainage
Optimum slope
Flat-to-undulating upland surface

14. The Soil Profile
 Soil varies in composition, texture, structure, and color at different depths. Soil horizons are zones or layers of soil. A soil profile is a vertical section through all the soil horizons.
• The A horizon is commonly know as topsoil.
• The B horizon is subsoil and contains clay particles washed out from the A horizon.
• The C horizon is between B horizon and unaltered parent material.

15. Soil Profile

16. Soil Types
Three common types of soil are pedalfer, pedocal, and laterite.
1. Pedalfer
• Best developed under forest vegetation
Usually forms in temperate areas that receive >63 cm/year (Mostly Eastern States)
• Accumulation of iron oxides and aluminum-rich clays in the B horizon
Remember Al=aluminum & Fe=Iron on Periodic table (pedAlFer)
Brown to red-brown in color

17. Soil Types Pedocal Laterite Accumulates calcium carbonate
Associated with drier grasslands
Found in drier western United States
Contain less clay than pedalfers because of drier climate and less chemical weathering
Light gray-brown color
Laterite
Hot, wet, tropical climates
Intense chemical weathering
Large amount of water removes most of the calcite and silica
Iron Oxide and Aluminum oxide are left behind
Orange-red color

18. Soil Erosion  Water erodes soil. HOW?  Rates of Erosion
• Human activities that remove natural vegetation, such as farming, logging, and construction, have greatly accelerated erosion.
Wind vs Water? Which do you think erodes quicker?
 Sediment Deposition
• Another problem caused by excessive soil erosion
Reservoirs fill with sediment.
• Sediments are contaminated by pesticides and fertilizers.

19. Controlling Erosion • Planting rows of trees called windbreaks
Terracing hillsides
Plowing along the contours of hills
Rotating crops

20. Mass Movements

21. Triggers of Mass Movements
 The transfer of rock and soil (regolith) downslope due to gravity is called mass movement.
 Among the factors that commonly trigger mass movements are saturation of surface materials with water, oversteepening of slopes, removal of vegetation, and earthquakes.

22. The Role of Gravity
Shear stress is the force of gravity acting on an object on a slope
always pulls straight down, perpendicular to the horizon
objects move downhill at some angle

23. Resistance to Movement
Cohesive strength-the resistance of an object to move downhill Friction
Cohesion, stickiness of particles
Other forces holding a particle in place (plant roots, cementation)

24. The Role of Water
Water may act to increase or decrease cohesive strength
Dry regolith or soil has little or no cohesion
Damp regolith or soil is sticky
Saturated regolith or soil flows easily

25. Types of Mass Movement Classified by Type of motion Type of material
Rate of movement

26. Types of Mass Movements
 Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement.
 Rockfalls
• A rockfall occurs when rocks or rocks fragment fall freely through the air.
Sometimes triggers other mass movements

27. Types of Mass Movements
 Slides
• In a landslide, a block of material moves suddenly along a flat, inclined surface.
• Slides that include segments of bedrock are called rockslides.
 Slumps
• A slump is the downward movement of a block of material along a curved surface.

28. Heavy Rains can Trigger Slumps

29. Types of Mass Movements
 Flows
• Flows are mass movements of material containing a large amount of water.
• Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete.
• Earthflows move relatively slowly and carry clay-rich sediment.

30. Types of Mass Movements
 Creep
• Creep is the slow, downhill movement of soil and regolith. This is the slowest type of mass movement.