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,
Fe3+, Al3+, Mg2+, Zn2+, Fe2+
dioctahedral: 2 Al
trioctahedral: 3 Mg
2.)
3.)
(4)
Match the colloid name with its mineral type:
a. Kaolinite
b. Vermiculite
c. Mica
d. Goethite
__y___
__x___
__z___
__q___
(2)
x. 2:1 expanding Si clay
y. 1:1 non-expanding Si clay
z. 2:1 non-expanding Si clay
q. non-Si clay
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 1:1
type clays and Fe/Al oxides and generally lower amounts of 2:1 clays: 1:1 type and Fe/Al
oxides clays have less isomorphous substitution thus less negative charge and less CEC.
Soil Aeration
Soil Aeration
I.
Process of Soil Aeration
II.
Characterizing Soil Aeration
III. Factors Affecting Soil Aeration
IV. Ecosystem Effects of Soil Aeration
I. Process of Soil Aeration
A.
O2 availability in field
1. soil macroporosity (texture/structure)
2. soil water content (proportion of porosity filled with air)
3. O2 consumption by respiring organisms (plant roots and
microbes)
B. Excess Moisture
1. water saturated/waterlogged: condition when all or nearly
all of the soil pores are filled with H2O
2. adaption
C. Gas exchange
1. mass flow
2. diffusion (Fig. 7.3)
Fig. 7.3 = diffusion
II. Characterizing Soil Aeration
A.
Composition
1. O2
2. CO2 (Fig. 7.8)
3. other gases
B. Air-filled porosity
1. ideal composition
2. O2 diffusion through water<<<<<air
C. Chemical redox potential
1. redox rxns
2. role of O2
3. other e- acceptors (Table 7.1)
Fig. 7.8 = CO2
II. Characterizing Soil Aeration
A.
Composition
1. O2
2. CO2 (Fig. 7.8)
3. other gases
B. Air-filled porosity
1. ideal composition
2. O2 diffusion through water<<<<<air
C. Chemical redox potential
1. redox rxns
2. role of O2
3. other e- acceptors (Table 7.1)
Redox Reactions
Table 7.1 = other e- acceptors
III. Factors Affecting Soil Aeration
A.
Drainage
B.
Rates of respiration
C. Subsoil vs. topsoil
D. Soil heterogeneity
E.
Seasonal differences
F.
Effects of vegetation
III. Factors Affecting Soil Aeration
A. Drainage
1. Why are macropores important to soil aeration?
B. Rates of respiration
2. What management activities can alter soil air composition?
C. Subsoil vs. topsoil
3. Why do subsoils have lower O2 concentrations than surface
soils?
D. Soil heterogeneity
4. How do O2 and CO2 concentrations change within a
profile?
5. What effect does tillage have on aeration?
E. Seasonal differences
6. Contrast spring vs. summer soil aeration.
F. Effects of vegetation
7. What is an effect of one specific type of vegetation on soil
aeration?
III. Ecosystem Effects of Soil Aeration
A.
Ecological
B.
Soil and plant management
C. Wetlands
Exam Review
• TEXTBOOK CHAPTERS
– anything covered in class
– suggested study ?’s
– calculations
• ASSIGNED READINGS
– suggested study ?’s
• FRIDAY DEMO/DISCUSSION/FIELD TRIPS
– handouts