Soil Aeration

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QUIZ 5 Answers 1.) Pick one of the two
building blocks of silicate clay minerals,
tetrahedron or octahedron. Describe its
elemental composition and what cations can be
replacement ions in isomorphous substitution.
Diagrams/pictures encouraged. tetrahedron 4O,
1Si, Fe3 or Al3 can replace Si4 octahedron
6O, dioctahedral 2 Al Fe3, Al3, Mg2, Zn2,
Fe2 (2) trioctahedral 3 Mg 2.) Match the
colloid name with its mineral type (4) a.
Kaolinite __y___ x. 21 expanding Si clay b.
Vermiculite __x___ y. 11 non-expanding Si
clay c. Mica __z___ z. 21 non-expanding Si
clay d. Goethite __q___ q. non-Si clay 3.) A
soil contains 5 humus, 10 vermiculite, 20
kaolinite, and 10 gibbsite. What is its
approximate cation exchange capacity? (Table 8.5
on reverse side.) (2) 27 cmolc/kg 4.) Data
from the Holmgren article showed that Ultisols
had the lowest CEC of all the soil orders
sampled. Does this make sense? Explain.
(2) yes, ultisols are very weathered
soils, which means they have generally larger
amounts of 11 type clays and Fe/Al oxides and
generally lower amounts of 21 clays 11 type
and Fe/Al oxides clays have less isomorphous
substitution thus less negative charge and less
CEC.
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Soil Aeration
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Soil Aeration

• Process of Soil Aeration
• Characterizing Soil Aeration
• Factors Affecting Soil Aeration
• Ecosystem Effects of Soil Aeration

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• I. Process of Soil Aeration
• O2 availability in field
• soil macroporosity (texture/structure)
• soil water content (proportion of porosity filled
  with air)
• O2 consumption by respiring organisms (plant
  roots and microbes)
• Excess Moisture
• water saturated/waterlogged condition when all
  or nearly all of the soil pores are filled with
  H2O
• adaption
• Gas exchange
• mass flow
• diffusion (Fig. 7.3)

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Fig. 7.3 diffusion
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• II. Characterizing Soil Aeration
• Composition
• O2
• CO2 (Fig. 7.8)
• other gases
• Air-filled porosity
• ideal composition
• O2 diffusion through waterltltltltltair
• Chemical redox potential
• redox rxns
• role of O2
• other e- acceptors (Table 7.1)

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Fig. 7.8 CO2
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• II. Characterizing Soil Aeration
• Composition
• O2
• CO2 (Fig. 7.8)
• other gases
• Air-filled porosity
• ideal composition
• O2 diffusion through waterltltltltltair
• Chemical redox potential
• redox rxns
• role of O2
• other e- acceptors (Table 7.1)

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Redox Reactions
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Table 7.1 other e- acceptors
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• III. Factors Affecting Soil Aeration
• Drainage
• Rates of respiration
• Subsoil vs. topsoil
• Soil heterogeneity
• Seasonal differences
• Effects of vegetation

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• III. Factors Affecting Soil Aeration
• Drainage
• Why are macropores important to soil aeration?
• Rates of respiration
• 2. What management activities can alter soil air
  composition?
• Subsoil vs. topsoil
• 3. Why do subsoils have lower O2 concentrations
  than surface soils?
• Soil heterogeneity
• How do O2 and CO2 concentrations change within a
  profile?
• What effect does tillage have on aeration?
• Seasonal differences
• 6. Contrast spring vs. summer soil aeration.
• Effects of vegetation
• 7. What is an effect of one specific type of
  vegetation on soil aeration?

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• III. Ecosystem Effects of Soil Aeration
• Ecological
• Soil and plant management
• Wetlands

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Exam Review

• TEXTBOOK CHAPTERS
• anything covered in class
• suggested study ?s
• calculations
• ASSIGNED READINGS
• suggested study ?s
• FRIDAY DEMO/DISCUSSION/FIELD TRIPS
• handouts