1. Ch. 7 Sec. 3
Formation of Soil

2. Soil Essential for life on earth Growing plants for food and oxygen
Homes for organisms

3. Development of Soil Soil development differs in each area
Soil is broken down rock particles and decaying organic matter: ____________
Provides nutrients to the soil
Chemical and mechanical weathering

4. Soil Composition Soil forms in layers Residual Soil
Parent soil is the solid bedrock from which other pieces break off
From Parent bedrock  weathering occurs
Soil composition differs depending on location
Residual Soil
Soil located above it’s parent material
Kentucky Blue grass soil

5. Soil Composition Transported Soil
Soil moved away from parent bedrock due to erosion
Proportions between soil and bedrock differ due to chemical weathering
Highly acidic areas have lower organic materials

6. Soil Profiles Vertical sequence of soil layers Soil Horizon
Poorly developed soils show little difference between layers
Soil Horizon
Three major  A, B, & C
The D layer is the Rock bed

7. Soil Profiles A: high concentration of organic matter & humus
Dark Colored
B: Sub-soils that are enriched with clay materials
Washed out materials from topsoil
Red or brown due to iron oxides
C: Above bedrock, contains weathered parent material

8. Topography Topography affects thickness of soil
Soils on slopes are thin due to run-off
Soils in lower valleys are thick
Slopes facing sunlight (South in N. hemisphere) have high vegetation and thicker soils

9. Soil Types Polar High latitudes and high elevations
Good drainage but very thin horizons: only cm’s thick
Permafrost (frozen ground) under polar soils

10. Soil Types Temperate Soils Able to support many diverse environments
Grassland  high in humus
Forest  high in aluminum rich clays

11. Soil Types Desert Soil Receive low levels of precipitation
High level of accumulated salts
Little organic matter  Very thin A Horizon

12. Tropical Soils Tropical Soil
High temps & high precipitation lead to infertile soil
Very little humus but high in iron and aluminum
High oxidation (red soil)
Poor growth conditions

13. Soil Texture Soil classified accord to size
Clay (smallest), silt, or sand (largest)
Texture of a soil affects its capacity to retain water and its ability to support growth

14. Soil Fertility How well soil can support plant growth Determined by:
1) Availability of nutrients
2) Number of Microorganisms
3) Amount of precipitation
Addition of limestone reduces acidity and enhance crop growth