1. Soil Formation Chapter 7 Section 3

2. Soil weathered rock particles & decaying organic matter (humus) weathered rock particles & decaying organic matter (humus)

3. Soil Formation soil forms in layers soil forms in layers smallest pieces of weathered rock on top with organic matter smallest pieces of weathered rock on top with organic matter rain water seeps through soil & leaches soluable minerals (carries them to lower layers) rain water seeps through soil & leaches soluable minerals (carries them to lower layers)

4. Soil Formation

7. Soil formation is a slow process that takes centuries Soil formation is a slow process that takes centuries

8. Soil Terms residual soil residual soil soil located above parent material (matched bedrock) soil located above parent material (matched bedrock) transported soil transported soil has been moved away from parent rock has been moved away from parent rock bedrock bedrock layer of rock beneath soil. layer of rock beneath soil. humus humus decaying plants and animals. decaying plants and animals.

9. Soil Composition dependent upon parent rock and type of weathering. dependent upon parent rock and type of weathering. A. Ingredients A. Ingredients 1. weathered rock - 80% (clay, quartz & nitrates) 1. weathered rock - 80% (clay, quartz & nitrates) 2. organic matter (humus) 2. organic matter (humus) 3. air & water in pore spaces 3. air & water in pore spaces B. Texture - size of soil particles B. Texture - size of soil particles 1. gravel - 2-64 mm in diameter 1. gravel - 2-64 mm in diameter 2. sand - 1/16 - 2 mm 2. sand - 1/16 - 2 mm 3. silt - less than 1/16 mm 3. silt - less than 1/16 mm 4. clay - smallest - only formed through chemical weathering. 4. clay - smallest - only formed through chemical weathering.

10. Soil Texture and Structure Point A: 10% silt 40% clay 50% sand Clay loam has no single particle size percentage that dominates!

11. Mature Soil Profile Mature Soil Profile A-horizon A-horizon aka: topsoil aka: topsoil dark colored, mostly organic (humus) dark colored, mostly organic (humus) B-horizon B-horizon Aka: subsoil Aka: subsoil leached out minerals from A. leached out minerals from A. Clay, some humus Clay, some humus C-horizon C-horizon partly weathered bedrock. partly weathered bedrock.

12. Profiles

13. Soil Types pedocal pedocal soil rich in calcium; found in drier areas as calcium doesn’t leach out soil rich in calcium; found in drier areas as calcium doesn’t leach out SW U.S. SW U.S. pedalfer pedalfer aluminum & iron rich; less fertile, calcium & other nutrients leached aluminum & iron rich; less fertile, calcium & other nutrients leached EasternU.S. EasternU.S.

14. Soil Types:

15. Soil Types

16. Soil Conservation The Dust Bowl helped people appreciate the value of soil. The Dust Bowl helped people appreciate the value of soil. 1930s, with government support, farmers began to take better care of their land. 1930s, with government support, farmers began to take better care of their land. Farmers adopted methods of farming that helped save the soil. Farmers adopted methods of farming that helped save the soil.

17. Dust Bowl

18. Soil Conservation Soil conservation is the management of soil to prevent its destruction Soil conservation is the management of soil to prevent its destruction Ways that soil can be conserved Ways that soil can be conserved Contour plowing is the practice of plowing fields along the curves of a slope. This helps slow the runoff of excess rainfall and prevents it from washing the soil away. Contour plowing is the practice of plowing fields along the curves of a slope. This helps slow the runoff of excess rainfall and prevents it from washing the soil away. Conservation plowing disturbs the soil and its plant cover as little as possible. Dead weeds and stalks of the previous year’s crop are left in the ground to help return soil nutrients, retain moisture, and hold soil in place. This method is also called low-till or no-till plowing. Conservation plowing disturbs the soil and its plant cover as little as possible. Dead weeds and stalks of the previous year’s crop are left in the ground to help return soil nutrients, retain moisture, and hold soil in place. This method is also called low-till or no-till plowing. Crop Rotation – farmers plant different crops in a field each year. This allows different nutrients to be taken from the soil each year instead of the same nutrients year after year. Some crops restore the nutrients. Keeps the soil from becoming nutrient depleted. Crop Rotation – farmers plant different crops in a field each year. This allows different nutrients to be taken from the soil each year instead of the same nutrients year after year. Some crops restore the nutrients. Keeps the soil from becoming nutrient depleted.

19. Soil Erosion Terms Overgrazing – allowing cattle and other grazing animals to strip the land of vegetation Overgrazing – allowing cattle and other grazing animals to strip the land of vegetation Deforestation – cutting down of large forest areas without replacing trees Deforestation – cutting down of large forest areas without replacing trees Desertification – process where soil is lost due to little rainfall and vegetation has been lost Desertification – process where soil is lost due to little rainfall and vegetation has been lost