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9.2 Soils

9.2 Soils. Where the geoshpere and the bioshpere meet. Learning Targets. Discuss why soil is an important resource Describe how soil forms from existing rocks Describe the different textures and components of soil Draw and describe a soil profile

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9.2 Soils

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  1. 9.2 Soils Where the geoshpere and the bioshpere meet

  2. Learning Targets • Discuss why soil is an important resource • Describe how soil forms from existing rocks • Describe the different textures and components of soil • Draw and describe a soil profile • Define 3 climate related soils: pedalfer, pedocal, and laterite.

  3. Soils – Characteristic #1 Composition varies with climate • Most important factor determining soil • Deserts 100% inorganic • Swamps 100% organic

  4. Soils – Characteristic #1 Increased weathering  greater soil formation • More rain  more chemical reactions • Increased rainfall  Increase dissolved rock • Increased temperature  Increase rate of chemical reactions • Warmer regions  Faster plant & bacteria growth

  5. Soils – Characteristic #2 Inorganic matter • 50% of most soils • Sediments, water, air • Determines porosity  drainage

  6. Soils – Characteristic #3 Organic matter – Biological Activity • 50% of most soils • Humus: rotting remains of dead organisms • Increases water holding ability • Increases fertility

  7. Soils – Characteristic #4 Home to millions of species

  8. Up to 3 billion organisms/gram

  9. Soil Formation - Overview • Depends on: • Climate: determines temperature, precipitation, and type of vegetation • Source rock: determines type of inorganic material • Topography: determines rate of erosion • Local organisms: can speed up or slow down the process; determines type of organic matter

  10. Identifying Soils Texture triangles are used to identify soil • % sand • % clay • % silt • Mixture of all 3 types  loam

  11. Soil profiles As bedrock breaks down, layers of soil form: • Horizon: one layer of soil • Profile: all horizons from bedrock to topsoil

  12. Soil profile • Depth varies widely from place to place • A Horizon • Topsoil: organic matter, humus, roots, organisms • B Horizon • Subsoil: clay, aluminum, iron • C Horizon • Source rock: bedrock beginning to weather

  13. Climate Related Soils • Every climate type has an associated soil • Most common climate related soils • Pedalfer • Pedocal • Laterite

  14. Pedalfer • Forests: a lot of rain • Trees that lose leave annually • Deciduous trees • Al and Fe rich  ped-Al-Fe-r • Fertile • High clay content

  15. Pedocal • Grasslands: dry seasons • Calcium rich  pedo-Cal • Less fertile • Low clay content • Soil forms very slowly; Why? • Less vegetation and no annual leaf loss means less organic matter

  16. Laterite • Tropical areas: hot, humid • Low nutrient content • Nutrients get dissolved by constant rain • Very thick, but not very fertile

  17. Pedalfer Pedocal Laterite

  18. Soil Conservation • Maintain plants • Protects from wind and water erosion • Provides organic matter • Good farming practices • Low-till farming • Proper irrigation  avoid salt accumulation • Crop rotation • Cover crops

  19. Erosion control farming

  20. Terracing

  21. No erosion control

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