1. 3.2 - Soils Discuss why soil is an important resource.
Describe how soil forms from existing rocks.
Describe the different textures and components of soil.

2. What is Soil?
Soil is a complex mixture of organic and inorganic materials.
Inorganic materials
weathered rock (pebbles, sand, silt, clay particles)
Organic materials
remains of partially decomposed plants and animals
Provides nutrients, such as nitrogen, needed for plant growth
Soil is an ecosystem unto itself.
Earthworms, bacteria, insects, fungi, etc. call soil home

3. Factors that Influence Soils
Climate
Rock Type
Topography
Biological Activity
Time

4. 1. Climate Most important factor determining soil type
Different rock types in a given climate produce similar soil
Warmer, wetter climates = greater rate of weathering
higher rate of chemical and mechanical weathering
Plants and bacteria grow faster
Thicker soils with more organic materials
Colder, drier climates = lower rates of weathering
Thin soils with less organic materials

5. 2. Rock Type (Parent Material)
Parent Material = source of inorganic materials
Chemical changes during soil formation depend on what minerals and rocks are present in the parent material.
Example: Calcium-rich soils generally form from calcium-rich rocks (like limestone) but not from calcium-poor rocks like granite.

6. 3. Topography
Loose soil stays in place in flat areas, allowing more thorough physical and chemical alteration of its grains.
On steep slopes, the soil moves downhill before complete alteration can occur.

7. 4. Biological Activity
Plant roots physically break rocks into small pieces.
Lichens dissolves rock.
Burrowing animals and insects mix the soil and help aeration.
Humus = the decayed remains of plant and animal life
increases the soil’s porosity and water holding capacity
helps to buffer rapid changes in soil acidity
helps the soil to hold its nutrients, increasing its fertility
Lichens
Earthworms in Humus

8. 4. Biological Activity

9. 5. Time
When bedrock is exposed at the surface, chemical, biologic, and physical processes combine to produce a thin soil layer.
Over time, the processes extend vertically downward, developing soil horizons whose position and thickness change over time.

10. Soil Texture and Composition
Permeability
ability of soil to allow water to flow easily through the spaces between soil particles
influenced by soil texture
Soil Texture
depends on particle size and proportion of particle types in the soil
particle types = sand, silt, clay, gravel

11. Identifying Soil Types by Texture
When soil scientists want to precisely determine soil type, they measure the percentage of sand, silt, and clay.
The soil type can then be determined from the location on the diagram.

12. Soil Profile The simplest profiles have only 3 soil horizons:
A Horizon (topsoil)
region of most intense biological activity
contains highest amount of organic material A
B Horizon (subsoil)
where soluble minerals and clays accumulate.
holds more water than the topsoil because of the presence of iron and clay minerals.
less organic material B
C Horizon
layer of partially altered bedrock
Pieces of the original rock are seen and can be identified. C

13. Types of Soils Influenced heavily by climate
Include pedalfer, laterite, and
pedocal

14. Soil Conservation

15. Soil Conservation Harmful Human Practices Deforestation Over-Farming
Pollution

16. Soil Conservation Positive Human Practices
Add organic materials to soils (compost, manure)
Crop rotation and Cover crops
Terracing
Planting trees as windbreaks
Plowing along contours of the field

17. Soil & Interaction of Earth’s Systems
Dew (moisture from the air) begins chemical alteration of parent rock
Rain erodes loose soil, preventing further alteration
Temperature controls rate and extent of chemical processes
Soils
Biosphere
Hydrosphere
Geosphere
Atmosphere
plants add and remove chemicals
plant roots anchor soil in place, enabling chemical reactions to be completed
animals mix soil; transport seeds, etc.
Water seeps into the ground, dissolving and redistributing elements
evaporation dries soil, changing its physical characteristics
solid rock and unconsolidated sediment are the parent material for soil
geologic processes (surface and internal) expose and bury rock, etc.