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SOIL FORMATION

SOIL FORMATION. Soil Formation. The Importance of Soil All life depends on the thin top layer of soil covering the earth’s surface. Topsoil provides: Support Water Air Nutrients. Weathering: Biological, Chemical, and Physical Processes. Weathering: Breakdown of Rock near the Surface.

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SOIL FORMATION

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  1. SOIL FORMATION

  2. Soil Formation • The Importance of Soil • All life depends on the thin top layer of soil covering the earth’s surface. • Topsoil provides: • Support • Water • Air • Nutrients

  3. Weathering: Biological, Chemical, and Physical Processes

  4. Weathering: Breakdown of Rock near the Surface Mechanical • Geological Activity – abrasion • often occurs to rocks in rivers, beaches, or desert areas • Glacial Activity • Expansion of ice • Effects of Temperature

  5. Erosion – by wind

  6. Erosion – by water

  7. Glacier Receding

  8. Wedging - Frost

  9. Weathering: Breakdown of Rock near the Surface Chemical Alteration • Carbon dioxide, sulfur dioxide and various nitrogen compounds from the air form acids when dissolved in water. These acids may react with the rock and increase breakdown.

  10. Chemical Weathering

  11. WeatheringBreakdown of Rock near the Surface • Organic Processes • Wedging – Plant Roots

  12. Wedging - Roots

  13. What Determines Soil Type • Climate • Vegetation • Drainage • Time • Parent Material • Residual - Transported • Least Important Factor for Mature Soils

  14. Soil Composition

  15. What determines soil type? Young Soils/Immature Soils • Strongest Influence Is Parent Material Mature Soils • Strongest Influences: Climate, Vegetation, Drainage

  16. Soil Formation and Generalized Soil Profile

  17. Soil Horizons and Profiles Soil Profile • Suite of Layers at a Given Locality Soil Horizons • Layers in Soil • Not Deposited, they are Zones of Chemical Action • Layers (horizons) of mature soils • O horizon: leaf litter • A horizon: topsoil • B horizon: subsoil • C horizon: parent material, often bedrock

  18. Principal Soil Horizons • O - Organic (Humus) Often Absent • A – Leaching • K, Mg, Na, Clay Removed • B – Accumulation • Absent in Young Soils • Distinct in Old Soils • Al, Fe, Clay (Moist) • Si, Ca (Arid) • C - Parent Material

  19. Soils of the U.S.

  20. Typical Soil Profile (Spodosol)

  21. Ultisols – Georgia Clay

  22. Physical Texture Porosity Permeability Humus Chemical pH *You need to know how to fix pH problems Nitrogen Phosphorous Potassium Soil Characteristics

  23. Porosity - the percentage of interconnected space in rock and soil that can contain water Permeability – the degree to which the pores in the rock or soil are connected together so that water can move freely

  24. Main Soil Textures

  25. Soil Formation vs. Soil Erosion Soil formation Takes hundreds of years to form 1 cm (0.4 inches) of soil Soil erosion Blown away in weeks or months from plowing and clearing forests – any time we leave the topsoil unprotected

  26. Topsoil Erosion Is a Serious Problem in Parts of the World • Soil erosion • Two major harmful effects of soil erosion • Loss of soil fertility through depletion of plant nutrients in topsoil • Water pollution in nearby surface waters where eroded soil ends up as sediment • Kills fish, shellfish • Clogs irrigation ditches, reservoirs, lakes, and boat channels • Eroded soil may also be polluted with pesticides and fertilizers

  27. Dust Bowl of the 1930’s

  28. China’s Dust Storms - 2006

  29. Soil Textural Triangle Practice Exercises % Sand % Silt % Clay Texture Name 75 10 15 sandy loam 10 83 7 _______________

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