Quiz 5 Answers

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• Quiz 5 - Answers
• 1.) a.) List the five master horizons for
  describing soil profiles.
• O, A, E, B, C (2)
• b.) What is an elluvial horizon?
• Horizon in which there has been movement OUT
  (exiting) of clays, Fe, Al, O.M. often
  designated master horizonE
• 2.) For the profiles at the bottom of the page
• a.) which soil formed in more than one parent
  material?
• B (2C) (2)
• b.) which soil has a transitional horizon?
• A (BC)
• 3.) Name one diagnostic horizon and give a
  brief description of it.
• (Table 3.1) examples (2)
• Argillic subsurface accumulation of high
  activity clays
• Natric subsurface accumulation of high activity
  clays with gt15 Na
• Mollic thick, dark colored, high B.S., strong
  structure
• Umbric same as mollic, but low B.S.
• 4.) Which soil is the least weathered and which
  soil is the most weathered?
• Oxisols, Alfisols, Mollisols, Entisols, and
  Inceptisols.

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Soil Colloids Chapter 8
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Primary Minerals

• Table 2.2 and Figure 2.4
• Remember definition of mineral
• general adjective to describe inorganic materials
  derived from rocks
• ex silicate clays
• specific noun to refer to distinct minerals found
  in nature
• ex quartz, feldspar

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Definitions

• colloids organic and inorganic matter with very
  small particle size and a correspondingly large
  surface area per unit of mass
• silicate clay colloid with Si in framework
• nonsilicate clay colloid withOUT Si in
  framework
• humus more or less stable fraction of the soil
  O.M. remaining after the major portions of added
  plant and animal residues have decomposed

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Definitions

• exchangeable ions
• cations Al3, Ca2, Mg2, K, H, Na
• anions Cl-, NO3-, SO42-
• crystal structure the orderly arrangement of
  atoms in a crystalline material
• amorphous noncrystalline

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Important Properties of Soil Colloids

• Size
• Surface Area
• Surface Charge
• Cation/Anion Exchange

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Four Major Types of Soil Colloids

• Inorganic
• 1) crystalline silicate clays
• 2) non-crystalline silicate clays
• 3) Fe/Al oxides (non silicate clays)
• Organic
• 4) humus

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Structure of Soil Colloids

• Silicate clays Fig 8.4
• Building Blocks
• tetrahedral
• 4-sided
• 1 Si, 4 O
• octahedral
• 8-sided
• trioctahedral 6O with 3 Mg2
• dioctahedral 6O with 2 Al3

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Fig. 8.4
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Isomorphic Substitution

• Definition the replacement of one atom by
  another of similar size in a crystal lattice
  without disrupting or changing the crystal
  structure of the mineral
• Table 8.2
• in tetrahedral sheets
• expected ions Si4
• potential replacement ions Al3, Fe3
• in octahedral sheets
• expected ions Al3, Mg2
• potential replacement ions Al3, Fe3, Mg2,
  Zn2, Fe2

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Structure of Soil Colloids

• Nonsilicate clays Fe/Al Oxides
• no Si
• octahedral only (no tetrahedral)
• little isomorphic substitution
• small negative, sometimes positive charge
• Humus
• noncrystalline
• large organic molecule (C, O, H, N)
• net negative charge
• Fig. 8.13

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Genesis of Soil Colloids

• alteration
• decomposition and recrystallization
• parent material and weathering conditions

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Soils An Introduction (Singer and Munns)