Exam 4 Study Guide
1. A 2:1 type clay mineral is made up of how many of each layer? 2 tetrahedral:1 octahedral
2. In the octahedral layer, this type of substitution can occur.
Mg for Al
3. This clay mineral is considered a 1:1 type. Kaolinite 4. The iconic radii of cations are smaller than anions. 5. Calculate the charge (CEC) associated with the following clay
mineral formula. Also, indicate whether it is negative or
6. Cation exchange capacity of soil organic matter increases
with increasing pH.
7. This soil component potentially has the greatest CEC,
8. Calculate the charge (CEC) associated with the following clay mineral formula. Also indicate whether it is negative or Don't forget about the age old question of What are barrier islands, and why are they important?
K1.4(Si6.4Al1.6)Al4O20(OH)4 Charge= 1.4-1.6=-.2
9. Differentiate between 2:1 and 1:1 type clay minerals in terms
2:1 (2 tetrahedral:1 octahedral) 1:1 (1 tetrahedral:1
10. What ions substitute for each other in tetrahedrals and
Tetrahedral: Al for Si Octahedral: Mg for Al
11. Describe pH dependent charge on functional groups of
Functional groups supply charge, majority of charge
from SOM, quantity of charge depends on pH. 12. What is the CEC of clay minerals and soil organic
matter? Increases with increasing pH
13. This cation has the greatest charge density and is held
the tightest by the CEC. Al3+
14. This clay mineral is the least weathered and contains
interlayer potassium. Illite
15. As an acid soil’s pH becomes greater (more alkaline), We also discuss several other topics like What is the economic model?
the CEC increases. We also discuss several other topics like Where is the water found on earth?
16. Which of the following indicates chemical equivalents?
3 cmol Ca2+= 2 cmol Al3+
17. Name two sources of pH dependent charge in soils.
Functional groups-soil organic matter, Al and Fe oxides 18. As soils weather and become more acid, this cation
increasingly becomes more adsorbed to the soil CEC. Al3+ 19. Functional groups of soil organic matter contribute most
to this type of acidity? Residual
20. As soils become more acid, availability of this
micronutrient decreases. Mo
21. Which of the following indicates chemical equivalents? 2 cmol K+ = 1 cmol Ca2+ If you want to learn more check out What is hang up by eva hesse?
22. Hydrogen held to functional groups of organic matter, broken edges of clays, and aluminum and iron
oxides/hydroxides is considered nonexchangeable. 23. Explain how charge density affects cation adsorption to
the soil CEC. Strength of attraction depends on charge
and size of cation.
24. Differentiate between the 3 types of soil acidity. a. Active acidity: solution phase H+, ionized from
organic and inorganic acids including Al hydrolysis. b. Exchangeable acidity: H+ and Al3+ on exchange
c. Residual acidity: non-exchangeable or bond Al3+ and H+. H+ on Al and Fe oxides. Al bound to organic matter and clays. H bound to functional groups of We also discuss several other topics like What is the total molecular equation?
SOM and edges of clay minerals.
25. Which micronutrients increase or decrease in
availability when soils become more acid?
Increase: Fe, Cu, Zn, Mn Decrease: Mo
26. Clay minerals are classified as crystalline/secondary. 27. In a tetrahedral layer, this substitution can take place.
Al for Si
28. A 2:1 clay mineral has 2 tetrahedral sheets. 29. Cations adsorbed to soil colloids are considered
30. Cation exchange capacity of kaolinite is primarily due to pH-dependent charges.
31. Soil conditions potentially having the greatest positive charges present would best be described as highly We also discuss several other topics like What is ceteris paribus?
32. Of the clay minerals, this one would have the greatest
total surface area, vermiculite.
33. Due to its effective diameter, this clay mineral would
not be found in the silt size fraction, smectite.
34. Lack of interlayer space in kaolinite is a result of H
35. Tetrahedral sheets share this oxygen position with
neighboring tetrahedrals, basal.
36. This clay mineral is considered to have the greatest
shrink-swell potential. Smectite
37. At pH 7.0, this soil component would have the greatest
38. With partial removal of interlayer potassium and the addition of some silicon, this mineral could form directly from
39. This clay mineral occurs in both tri- and di-octahedral
40. Early weathering of muscovite would would most likely
result in this type of clay? 2:1
41. Due to its size, this cation fits in the “hexagonal hole”
within the interlayer of fine-grained micas. K+
42. Exchangeable aluminum is best represented by this species. Al3+
43. Anion concentration in soil dominated by permanent charge would be the greatest in the diffuse solution
44. Liming an acid soil would have what effect on the CEC?
45. Through the hydrolysis, how many moles of acidity (H+)
are produced from one mole of Al3+? Three
46. Availability of this micronutrient increases with liming or
an increase in soil pH. Molybdenum
47. To be labeled or sold as dolomitic lime in Mississippi,
the material must contain a minimum of 6% Mg. 48. Exchangeable aluminum is best represented by this ion.
49. Evidence for the possible influence of man’s activities
on acid rain occurs at the pH of <5.6.
50. High soluble levels of this element in lakes interferes
with oxygen assimilation in the gills of fish. Al3+
51. Increasing soil acidity affects the activity of this microbe
the least. Fungi
52. This soil organism is capable of photosynthesis,
53. This organism lives in modified root tissue of legume
and fixes N2. Rhizobium
54. This temperature is defined as biological zero due to limited microbial activity, 41°F.
55. This group of soil microbes is most active in the
decomposition of complex woody type plant material, fungi. 56. Which of the following has a eukaryotic cellular
57. This organism is noted for infecting roots and increasing
water and nutrient availability to plants. Mycorrhizae 58. What would be predicted to improve what are referred
to as “soil health” properties such as biological diversity?
59. The ‘night crawler’ earthworm is noted for its contribution to improved soil fertility, porosity, and
60. Which crop residues would have the highest C:N ratio? 61. When crop residues are added to soil, approximately
how much of the carbon as CO2 is released back to the
atmosphere through decomposition? 60%
62. The active organic matter fraction of the A horizon
would be the lowest in yearly plowed soil.
63. With increasing depth, the C:N ratio decreases. 64. These soil conditions would result in the greatest soil
organic matter given all other factors being equal. Poorly
65. Which of the following anions is adsorbed to soil with
the greatest strength? PO43-
66. Soil fixation of P occurs
67. This nutrient is very important for water use efficiency
and drought resistance. K
68. These two nutrients contribute to eutrophication of
bodies of water.
69. The original mineral source of soil P is Apatite. 70. Net immobilization of soil ammonium and nitrate can
occur when crop residues added to the soil have a C:N ratio
71. Losses of N as NH3 are more likely to occur when urea
fertilizer is added to soil with a pH of >7.3.
72. Organic N in soil and crop residues initially undergoes
decomposition to NH4+.
73. In the conversion of NH4+ to No2- , the oxidation state of
the N changes to +3.
74. Nodules on the roots of legumes actively fixing N2 from
the atmosphere have this color. Pink to red
75. Mineralization of N occurs under these conditions?
Aerobic and Anaerobic
76. Nitrogen loss from soil does not occur by this process.
77. The degree of eutrophication occurring in fresh bodies
of water is limited by what nutrient or nutrients?
78. Which nutrient is most important in energy
relationships in plants? P
79. What is the mobility of potassium in plants? Mobile 80. Nitrogen is added to soil through rainfall because of
81. When crop residues are added to soil, approximately how much of the carbon as CO2 is released back to the
atmosphere through decomposition 60 to 80 %.
82. The valence state of N in NO3- is +5.
83. With increasing soil depth, the C:N ratio decreases. 84. Given all other soil conditions are the same, which soil
drainage class would result in the greatest organic matter
85. The Mississippi State Extension Service Soil Testing Lab
reports available S based on what? % of organic matter 86. Expressed as CEC, a soil containing 3200 lb Ca2+/ acre
would have how many cmolc/kg attributed to this cation? 8.0 87. Typically this nutrient is the most limiting factor for
eutrophication of bodies of freshwater in the US? P 88. This plant nutrient is noted for its role in drought
89. The most strongly fixed soil P is found in this form in soil. Inner sphere adsorbed.
90. The type of structure for the classification “strong medium angular blocky” is angular blocky.
91. This soil order comprises the most acreage in the southeastern U.S. , Ultisol.
92. Soil material that has an effective diameter of 0.5- to 1.0-mm would be classified as ______________.
93. The soil textural class ‘loam’ most accurately describes the soil texture where the soil separates are equal in their contribution to soil physical properties.
94. For a given volume of soil, as particle size decreases surface area increases.
95. What are the effects of drainage on soil color? Reds are good drainage, Yellow intermediate drainage , Greys are poor drainage
96. Explain the difference between dispersion and flocculation of soil particles. Dispersion is the separation of soil particles; flocculation is the joining of soil particles.
97. Define macropores and micropores relative to drainage?
98. What are the effects of soil texture on bulk density; 5. Pore size distribution?
99. This soil color would indicate poor drainage and the presence of reduced iron…grey.
100. Excessive quantities of this cation in soil causes the greatest dispersion. Na+
101. The diameter of micropores is considered to be less than 0.08 mm.
102. Which of the following pore size distributions (ratio of macro to micropores) might indicate a coarse or sandy soil texture? 65/35
103. In their native well aggregated state, this soil textural class generally has the lowest total pore space. _____________.
104. Field capacity occurs at a soil water potential of -0.33 bars.
105. A soil with a bulk density of 1.42 g/cm^3 and holds 26% volumetric (Pv) at field capacity would have a macropore space of approximately 20%.
106. Hydraulic conductivity (K) of soils depends greatly on soil texture and water content.
107. For three soils, all at a water potential of -0.3 bars, this texture would have the greatest volumetric water content. Clay loam
108. All capillary water in soil is considered to be plant available. True
109. Available water occurs within the soil water tension ranges of -0.1 to -15 bars.
110. A soil with a bulk density of 1.27 g/cm3 and holds 32% volumetric water (Pv) at field capacity would have a macropore space of approximately what? (1-
(1.27/2.56))x100=50.4 then 50.4- 32=18% so ≅ 20%
111. Hydraulic conductivity (K) of soils depends greatly on soil texture and water content.
112. For three soils all at a water potential of -0.3 bars, this texture would have the lowest volumetric water content sandy loam.
113. Capillary water occurs in micropores only. 11