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Weathering and Soils

Weathering and Soils . Weathering Breakdown of Rock near the Surface Due to Surface Processes. Chemical Alteration Solution & Leaching Biological Action Hydration Mechanical Impact Wedging: Frost, Plant Roots, Salt Crystal Growth, Expansion of Hydrated Minerals.

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Weathering and Soils

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  1. Weathering and Soils

  2. WeatheringBreakdown of Rock near the Surface Due to Surface Processes Chemical Alteration • Solution & Leaching • Biological Action • Hydration Mechanical • Impact • Wedging: Frost, Plant Roots, Salt Crystal Growth, Expansion of Hydrated Minerals

  3. Salt Crystallization, Utah

  4. Never Safe From Weathering

  5. Weathering Rates

  6. Differential Weathering and Erosion

  7. Differential Weathering and Erosion

  8. Surface Area and Weathering

  9. Surface-Volume Effects

  10. Spheroidal Weathering

  11. Spheroidal Weathering and Exfoliation

  12. Spheroidal Weathering

  13. Joints and Spheroidal Weathering

  14. Cavernous Weathering

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

  16. Soil Formation Processes Leaching from Surface • K, Mg, Na • Ca • Si • Al, Fe Accumulation beneath Surface • Al, Fe in Humid Climates • Ca in Arid Climates

  17. Soil Horizons and Profiles Soil Horizons • Layers in Soil • Not Deposited, but Zones of Chemical Action Soil Profile • Suite of Layers at a Given Locality

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

  19. Limits of Soil Formation Balance Between: • Downward Lowering of Surface • Downward Migration of Horizons If erosion rapid or soil evolution slow, soils may never mature beyond a certain point. Extremely ancient soils may have lost everything movable

  20. Soil Classification This may be the most difficult classification problem in science because of the many factors involved. Varied Bases for Classification • Parent Material • Special Constituent Materials • Maturity • Structure • Climate & Vegetation Multiple Objectives • Scientific • Genesis & Evolution • Agricultural • Fertility • Most Effective Use • Engineering • Slope Stability • Expansion and Shrinkage • Stability of Excavations

  21. "The 7th Approximation" • U.S. Soil Conservation Service • 12 Soil Orders

  22. "The 7th Approximation"

  23. Soils of the U.S.

  24. Typical Soil Profile (Spodosol)

  25. Aridisol, Kuwait

  26. Ultisols:AlabamaTennessee

  27. Kaolinite, Georgia

  28. Oxisol, California (a Paleosol)

  29. No O Horizon

  30. Paleosol, Scotland

  31. Loess • Silt-sized • Derived from Glacial Outwash in U.S. • Found in U.S., E. Europe, China • Parent material of world’s prime agricultural soils • Available nutrients • Fine size – lots of surface area • Cohesive – good root support • Porous – retains water well • No Rocks!!!! Windblown silt is called loess

  32. Loess, Wisconsin

  33. Loess in the U.S. Loess is the raw material for many mollisols, the best agricultural soils

  34. Loess in Europe Loess is the raw material for many mollisols, the best agricultural soils

  35. Loess in China Loess is the raw material for many mollisols, the best agricultural soils

  36. Impacts of Soil Loss • Lessened agricultural productivity • Respiratory hazards (wind erosion) • Siltation of streams • Wetland loss • Destruction of fish habitat • Obstruction of navigation • Eutrophication • Chemical pollution

  37. Controlling Soil Loss • Windrows • Retain vegetation cover • Contour plowing • Strip cropping • No-till agriculture • Sediment dams

  38. Strip Cropping and Contour Plowing

  39. Strip Cropping and Contour Plowing

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