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Rock Weathering and Soil Mineralogy

Rock Weathering and Soil Mineralogy. Physical Weathering……. Weathering A . Chemical Weathering Water is critical (and heat serves as a catalyst) Complex Process (involves several reactions) Biological Activity (helps accelerate weathering processes). Complex Process Solution Hydrolysis

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Rock Weathering and Soil Mineralogy

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  1. Rock Weathering and Soil Mineralogy

  2. Physical Weathering……

  3. Weathering A . Chemical Weathering • Water is critical (and heat serves as a catalyst) • Complex Process (involves several reactions) • Biological Activity (helps accelerate weathering processes)

  4. Complex Process • Solution • Hydrolysis • Oxidation • Hydration • Chelation • Dialysis • Chemical Reconstitution

  5. The negative log of hydrogen ion content

  6. Why does it matter?

  7. Why does it matter? Most Mobile Least Mobile Ca2+ > Na+ > Mg2+ > K+ >Si4+>Fe3+> Al3+

  8. Molar BA Ratio

  9. Molar BA Ratio Uncle Festus Cuzzin Cletus

  10. Molar BA Ratio Moles of Na2O + K2O + CaO + MgO Moles of Al2O3

  11. Cation Exchange Capacity (CEC): The amount of exchangeable cations that a given weight of soil is capable of holding

  12. CEC is measured in units of Cmol/kg, which replaces milliequivilents (meq)/100 g.

  13. CEC is measured in units of Cmol/kg, which replaces milliequivilents (meq)/100 g. Wt. of 1 meq. = mole weight (g) charge of ion * 1000 Ex: the weight of 1 meq. of calcium is: 1 meq. Of Ca2+= 40.08 g = 0.02 g (2) * 1000

  14. Ex: the weight of 1 meq. of calcium is: 1 meq. Of Ca2+= 40.08 g = 0.02 g (2) * 1000 So….the CEC of a soil containing 1.0316 g of exchangeable Ca2+per 100 g of soil is: 1.0316 g (wt. of exchangeable Ca2+) 0.02 (wt. of 1 meq. of Ca2+)

  15. Ex: the weight of 1 meq. of calcium is: 1 meq. Of Ca2+= 40.08 g = 0.02 g (2) * 1000 So….the CEC of a soil containing 1.0316 g of exchangeable Ca2+per 100 g of soil is: 1.0316 g (wt. of exchangeable Ca2+) 0.02 (wt. of 1 meq. of Ca2+) = 51.58 meq. =51.58 meq. Per 100 g, or 51.58 Cmol+/kg

  16. C. CEC Capacities

  17. Base Saturation

  18. Base Saturation: the percentage of cation exchange capacity of a soil occupied by basic cations. Why important? Plant growth Plant protection

  19. Ultisols Alfisols Mollisol

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