Soils Test Chapter 8

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jenmuz
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215279
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Soils Test Chapter 8
Updated:
2013-04-23 08:03:02
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AGN 215 Soils Test Chapter
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Soil Chemistry, Chapter 8
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  1. pH dependent sites
    ionization of hydrogen
  2. humus
    organic colloid
  3. chlorite
    2:2 non-expanding clay
  4. illite
    2:1 non-expanding clay
  5. kaolinite
    1:1 non-expanding clay
  6. soil nitrogen component
    percent organic matter
  7. amorphous soil compound
    allophane
  8. octahedron
    eight-sided clay structure
  9. vermiculite
    2:1 limited expanding clay
  10. Al/Fe oxide clays
    tropical clays
  11. montmorillonite
    2:1 highly expanding clay
  12. tetrahedron
    four-sided structure
  13. space between tetrahedral and octahedral sheets
    interlayer
  14. The area right next to the atoms, on the edge of the interlayer
    • internal surface area
    • they repel so water, other cations come in
  15. the storehouse where nutrients are adsorbed
    cation exchange capacity
  16. Name the 5 silicate clays we studied
    • kaolinite
    • montmorillonite
    • illite
    • vermiculite
    • chlorite
  17. what are some non-silicate colloids?
    • oxide/hydroxide clays (tropical)
    • amorphous materials (noncrystalline, volcanic ash, lava)
    • humus
  18. as a pH nears 7, what happens to the ionization amount?
    • it's greaterĀ 
    • we're talking about how close H is to O. The lower the pH, the tighter the bond between H and O
  19. isomorphous (ionic) substitution
    • in tetrahedral or octahedral sheets
    • referred to as constant or permanent negative sites (not affected by pH)
    • in octahedral, the most common sub is Mg
  20. the number of negative charges determines what?
    CEC
  21. What elements are most common in silicate clays?
    • Si4+
    • Al3+
    • Fe 3+
    • Mg 2+
    • Zn 2+
    • Fe 2+
  22. The lower the pH...
    • the higher amounts of H
    • also the more acidic
  23. 4 key things to remember about kaolinite
    • 1. 1:1 clay structure (1 tetra, 1 octa)
    • 2. No substitution in tetra or octa sheets
    • 3. Non-expanding
    • 4. Low CEC
  24. expansion of clays occurs where?
    • interlayer
    • if H moves into the interlayer, it's going to be attracted to the top and bottom of the sheet, oxygens are tightly held so there's no expansion
  25. 4 key things to remember about montmorillonite
    • 1. 2:1 clay structure
    • 2. ionic substitution in tetra and octa sheets - but mostly octa
    • 3. highly expanding clay
    • 4. High CEC
  26. 4 key things to remember about Illite?
    • 1. 2:1 clay structure
    • 2. Ionic sub in the tetrahedral sheet (sub Al3+ for Si4+)
    • 3. Non-expanding clay
    • 4. Moderate CEC
  27. Vermiculite - 5 things
    • 1. 2:1 clay
    • 2. ionic subs in tetra and octa (little more in tetra)
    • 3. interlayer space contains strongly adsorbed hydroxyions of Mg (mainly) and Al
    • 4. limited expanding clay
    • 5. very high CEC
  28. common sub in tetrahedral sheet?
    Al for Si
  29. common sub in octahedral?
    Mg for Al
  30. 5 things to remember about Chlorite
    • 1. 2:2 structure
    • 2. Ionic substitution in octahedral layer
    • 3. Mg-dominated octahedral sheet in interlayer
    • 4. Non-expanding
    • 5. Low to moderate CEC
  31. 5 things to know about humus?
    • 1. non crystalline
    • 2. CHO framework
    • 3. Large number of negative sites (compared to clays)
    • 4. pH dependent sites (H moves away from O)
    • 5. Very high CEC
  32. Oxide-hydroxide clays
    • sesquioxides
    • crystalline or amorphous
    • nonsticky, nonplastic, noncohesive (well-drained clays)
    • small negative charge (CEC)
    • small positive charge (AEC)
  33. Amorphous inorganic compounds
    • Noncrystalline
    • some oxide clays
    • allophane & imoglite
    • positive and negative sites
    • origin - volcanic compounds and some igneous rocks
  34. CEC calculations are based on
    • clay content
    • type of clay
    • humus content
    • PH
  35. CEC summation method
    • summation of all cations adsorbed on soil colloid
    • method used on mo soil testing report
  36. Base-forming cations (raises pH)
    • Ca
    • Mg
    • K
    • Na
  37. Acidic cations (lower pH)
    • H
    • Al
    • NH4

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