FIRST EXAM STUDY QUESTIONS
1. Discuss some of the reasons for the observed cation
exchange phenomena in soils.
2. What are the origins and relative magnitudes of the negative
charges of the soil inorganic fraction?
3. Under what circumstances might a soil be expected to take
on a net positive charge?
4. Why do certain clay minerals expand in water while others
do not? Give examples.
5. What is the so-called pH-dependent cation exchange
capacity and what causes it?
6. What is meant by the terms 1:1 and 2:1 minerals?
7. To what extent do the expandibility and particle
size of clay minerals affect the CEC?
8. Soil A is found to have a cation exchange capacity of 40
cmol kg-1. Soil B has a CEC of 15 cmol kg-1.
Textural analysis shows that
both soils contain approx. 75% sand and silt. What can you infer about
9. In a table headed
make-up of the colloidal fractions
of the two soils? Give reasons for your inferences.
CEC (cmol kg-1)
at least four common soil constituents and give their properties.
Discuss how the various properties affect measured
10. What is an Isoelectric
Point? From whence does it arise (in soils)? What role does
it play in soils?
11. List four common soil colloidal constituents and discuss their
respective impact upon soil chemistry.
12. What is the difference between a dioctahedral and a trioctahedral
mineral? Give some examples of each.
13. What is the difference between hydrolysis and hydration?
Give examples of each.
14. Explain the concept of weathering. What occurs during this process?
Why are some minerals more resistant to
than others? How can this be related to soil formation?
15. How might one predict
the process of weathering and secondary mineral formation without making
a long period of time?
16. What is soil organic
matter? Why is it important to know something about this material? What
components of the soil
matter are most important in soil chemistry?
17. Why is concentration
insufficient for studying soil chemical reactions? What is used instead?
18. Explain complexation. What is the difference between inner sphere and
outer sphere complexation?
19. What is an equilibrium constant? How do solubility products,
complexation products, acid dissociation products,
able to define the terms used in class.
21. Three processes were
listed as being of primary importance in weathering of minerals, these
Explain and give examples of how each
will be a factor in weathering of minerals in the soil.
22. When discussing weathering,
the formation of secondary minerals in soils formed from igneous rock
was shown to be a function of average annual rainfall.
Explain why this should occur.
23. The cation exchange capactiy
of Mica, which has a very high unit crystal charge, can be only about twice
which has no unit crystal charge, whereas the cation exchange capacity
of smectite, with an
unit crystal charge, can be 10 times higher than that of kaolinite. Explain
24. Why are we constantly relating
mineral solubility to pH?
25. Solubility of minerals can be plotted as activity diagrams, and would
describe a line on a two dimentional
plot and a
plane on a three dimentional plot. If the solution is in equilibrium with
the solid phase activity
of the plotted
components must fall on the line or plane. How does one interpret data
which falls above or below
If two different minerals are plotted in the diagram what kind of interpretations
can be made if
the two line/planes
are different and parallel? If they cross somewhere in the plot?
26. Aluminum is considered to
be an acid component of the soil. Why should this be true?
EXAM 2 AND 3 STUDY QUESTIONS
1. Discuss some of the reasons for the observed cation exchange
phenomena in soils.
2. Draw a diagram for a "typical" soil titration curve. Explain why such
a curve is obtained.
3. You would like to cause a
dispersed colloidal suspension to flocculate. How would you proceed? What
of your method (ie. why does it work?). Hint: colloids usually remain suspended
as a result of
4. What kind of problems may arise in measuring the pH of colloidal systems.
5. Indicate a few factors that can influence a measured CEC and explain
6. Statement: For best plant growth, one should always be sure the pH is
between 6.5 and 7.0. Comment.
7. Explain how variations in the thickness of the double layer might affect
8. Explain the ion-selectivity concept and indicate its importance in soil
chemistry and plant nutrition.
9. Discuss the importance of the "suspension effect" in soil chemical problems.
10. Some years ago the "Shultz-Hardy rule" was formulated. Basically, this
says that as valence of the saturating cation
clays become progressively better flocculated. How might this phenomenon
affect soil chemical
11. Explain the difference between the Helmholtz, Gouy, and Stern theories
of the clay surface. Indicate how
these theories might lead to different interpretations
of soil chemical relationships.
12. What soil properties and/or constituents determine it's buffering
capacity? Explain how the properties
(or constituents) listed exert
their influence on soil buffering.
13. What is the complimentary ion
effect? How does understanding this phenomenon assist our understanding
of plant nutrition?
14. Assume you are addressing
a group of farmers and business persons who are not so conversant with
plant nutrition, soil fertility and nutrient pollution problems. Your missionis
to explain to this
nature of cation exchange and why it is important. How would you proceed?
15. Assuming the Stern model of the electric double layer is correct, explain
(with help of diagrams) how the double
and zeta potential might change with increasing electrolyte concentration
and increasing valence
16. Given: A "typical soil profile might have pH values approximating the
from surface (in.)
knowledge of aluminum chemistry in aqueous systems, in which horizon(s)
would you expect to
find the most
Al? The least Al? Why?
17. If you search the literature,
you will find that soil pH is reported to the nearest tenth about half
the time and to
hundredth the other half. In fact it is not impossible to occasionally
find soil pH reported to the
thousandth of a pH unit. Comment on the appropriateness of such presentations.
18. Soil pH is highly important
in the proper growth of many plants, so soil scientists have expended considerable
on understanding soil reaction and the amount of lime required to establish
an optimum pH. Discuss
pH" concept, and some the soil factors influencing pH and lime requirement.
19. Describe the Quantity/Intensity
approach to soil testing. What are the advantages and/or disadvantages
compared to other methods we have discussed?
20. How and why does Al
enter the soil acidity picture?
21. An acidic pesticide of pK
5.0 is being applied to soils of a given region. Would leaching be greatest
for soils of
a) pH > 5,
b) pH 6 to 8, or
c) pH < 5?
22. What is the difference between specific and non-specific adsorption
23. One of the introductory comments
for this course was that soil is both a sink and source for ions. On the
basis of what
you have learned so for, give reasons for such a statement. Using
a specific ion, discuss the
which will occur as the soil becomes either a sink or a source.
24. Let us assume that we could find four soils formed under identical
circumstances, except that the soil
had been progressing for 103, 104, 105,
and 106 years. Let us further assume that the parent
of all four soils are mica-rich granites. How would you expect these soils
to differ chemically and
25. If the above soils had never
been fertilized, what differences might they exhibit in ability to supply
26. A practice finding increasing
favor is the use of soils as a terteriary treatment system for sewage effluent.
is of particular interest in this regard, since it has been cited as a
causative factor in surface
What soil properties should one consider in determining how effective a
soil would be
of phosphorus, and why?
27. Now, consider the welfare
of plants rather than water quality. What are some of the factors one needs
the waste water to soils, and why? Remember, the effluent will contain
a wide variety of inorganic
the exact contents being dependent upon the domestic/ industrial mix of
wastes being treated.
28. During the summer months,
deep lakes tend to form a thermal stratification with a very sharp boundary
above and cold water below. It has been found that gasses do not
readily diffuse from one temperature
zone to another,
so the lower layer is normally depleted in oxygen. Let us assume the lake
is well along its way in
process, so there is a plentiful amount of organic matter in the bottom
sediments to serve as
energy source. Discuss the type of chemical reactions which will occur
in the "soil" at the lake bottom
and the resultant
effect on overlying water quality.
29. A particular soil may contain up to 3% K, yet plants growing on the
soil might show good response to potassium
However, the same plant species growing on a soil containing less K might
show less response to K
Explain, including in your discussion a discussion of why various soils
differ in their ability to
for plant needs.
30. Mr. Smith always had a nice looking front lawn. However, one evening
he noticed that his neighbor, Mr. Jones'
was several shades greener than his own. This would never do! The next
morning, he proceeded forthwith
to the local
Agway store and bought two bags of urea (anyone knows that a green lawn
requires plenty of N), which
spread on the lawn. He couldn't help gloating a bit as his lawn, within
a week, became considerably
Mr. Jones'. However, to his horror, the dark green slowly changed to maroon,
indicating P deficiency.
In terms of
reactions occurring in the soil, explain what happened. What would you
recommend be done to correct the
What plant nutrients other than P might have been affected?
31. You have probably seen dead trees in the middle of Beaver ponds, drowned
corn in low, wet spots, etc. In fact, most
quite unhappy with wet feet. In terms of soil chemical reactions, what
might cause plants to die when the
32. During the semester, we have
periodically discussed and mentioned ion selectivity as it relates to chemical
in soils and
plant nutrition. What is ion selectivity? Give a few situations in
which selectivity might be important
the importance in terms of soil reactions.
33. The mineral fraction of highly weathered soils such as those found
in Southern United States and in tropical regions
made up of kaolinite and sesquioxides. What effect does this have on plant
34. Discuss the soil reactions and relationships that would likely result
from liming an acid soil (say pH 4.5) to
pH 7.0 and
maintaining the pH at the higher level.
35. Discuss the chemistry of iron and aluminum and explain their importance
in soil chemical equilibria.
36. Explain how the five soil forming factors (time, temperature, parent
material, vegetation, and topography) might
chemical characteristics of soils.
37. A modern fertilizer might typically contain such materials as KCl,
(NH4)2 HPO4, and Ca(H2PO4)2.
fate of these
materials when added to a soil at pH 6.5.
38. Discuss the weathering of mica as it pertains to reactions in the soil.
39. Why is Al considered a soil acid?
40. What type of soil factors
are involved in adsorption of organic "pollutants" such as pesticides?
41. In temperate region soils, the amount of buffering tends to be proportional
to the aluminum content of a soil.
42. The potassium cycle in soil is relatively simple, and can be roughly
divided into three categories:
1) exchangeable K, which is on the exchange complex, and available to plants;
2) K occurring as a part of the mineral structure, and completely unavailable
3) a "fixed" fraction which is not really considered as "mineral K", but
is not readily available
to plants either.
factors that influence the relative amounts of K in each of these fractions
and why the K is thus affected.
43. There is evidence that phosphorus adsorption by soils is related primarily
to organic matter and aluminum in the
the types of reactions that might be occurring and the implications to
availability of phosphorus
added to the soil.
44. Although the major emphasis of this course has been on inorganic reactions
occurring in the soil, the impact of the
has frequently been mentioned. Discuss the extent to which availability
of the three major plant
N, P, & K, are affected by soil organic mater. Include a discussion
of the reactions that will be
45. It has been shown that soils exhibit ion selectivity. How might this
affect availability of K to plants? What
soil pH likely have on the indicated relationship Why?
46. Along with aluminum, iron has frequently been mentioned as an important
element in soil chemical reactions. In what
types of reactions
is this element important and how is its influence "felt"?
47. Nitrogen, phosphorus, several heavy metals and trace elements, and
various organics such as pesticides or
can become potential soil problems. Restricting yourself to N and
heavy metals what are the potential
in using soils for disposal of materials containing these pollutants?
Why would it likely be
48. To a pH 5.0 solution in equilibrium with solid phase variscite (A1P04@2H20)
one adds calcium carbonate (CaC03).
discuss predicted changes that will occur in the system, including equilibrium
49. For a variety of reasons, no-till agriculture is becoming popular in
eastern U.S. Discuss the soil chemical changes
occur when "conventional" tillage practices (i.e. turning over the surface
6-8 inches and tilling
to a satisfactory
seedbed) are replaced by "no-till" practices (i.e., only a strip wide enough
to plant the seed
Growing vegetation is usually killed with herbicides). Also, discuss any
needed changes in fertilizer
50. What are the common electron acceptors for soil? Under what conditions
does each become important? What effect
conditions have on plants and microbes?
51. As ocean dumping of wastes has been curtailed by EPA, increasing pressure
for land disposal has been exerted.
This is no
real problem if the waste is a sludge from a waste-water treatment plant
serving an entirely domestic
since the sludge is not likely to be very different from animal manure.
However, if the plant serves
community, a high probability exists that the sludge contains potentially
toxic heavy metals. What
are the potential
problems involved in using soils for disposal of sludges containing heavy
metals? How would soil
be involved with the problem and with solutions?
52. What reactions are responsible for retention/fixation of phosphorous
in acid soils? Basic soils?
53. Indicate the sequence of events that occur upon exclusion of gaseous
oxygen from a soil by waterlogging.
be the approximate E7 for each event? How (and why) would you
expect biological systems to be affected
by this sequence
54. Explain why measurement of total soil analysis practiced in the early
1900's proved to be a poor indicator of the
ions which may enter the food chain.
55. Farmers report that when they shift cultural practices from the reliance
upon "Manufactured" fertilizers and
which has developed since WW II to the more traditional "organic" methods
of crop rotations, proper
of organic wastes (e.g. distribution of manure at 2-3 tons per acre
rather than disposal of manure at up
to 40-50 tons
per acre), use of "rock flours' as fertilizers, etc., they experience a
near-catastrophic drop in crop
first year, followed by a slow recovery. After about 3 or 4 years the yields
are nearly back to
levels, where they tend to stabilize. If you read Rodale Press and other
similar publications, you
phenomenon is attributed to a "poisoning" of the soil. However, much of
the effect can be predicted and
on the basis of the soil chemistry. Please do so.
56. Jackson has called aluminum reactions the "unifying principal in soil
science". If this is true, then all soil
should, in some way be related to aluminum chemistry. Recognizing that
many soil reactions are similar
to those of
either P or K, explain how aluminum reactions will affect plant availability
of these two nutrients.
57. A farmer/gardener alters his cultural practices to incorporate more
organic matter into the soil. List some of the
may have on inorganic reactions within the soil and/or availability of
nutrients to plants. In each
indicate why or how the effect occurs.
58. Describe the sequence of events (chemically) that occurs when a soil
becomes anaerobic. How does this affect
of nutrients to plants? Recognizing that lake or ocean sediments are "soils
under water" and streams
originate in marshes, how would this affect water quality?
59. Most soils contain far more potassium than is available at any one
time. What are the processes causing the
potassium to become available? Under what circumstances might the
potassium revert to a less available
60. On the basis of equilibrium chemistry, discuss the soil solution changes
that might be expected to occur when a
of phosphorus is added to the soil as fertilizer.
61. Discuss the soils' role in cycling K in the food chain.
62. Over recent years there has been an increasing concern about the impact
of so-called "acid precipitation" on the
Because managed ecosystems (eg. farms) include practices which counteract
soil effects, impact on soil
restricted to natural ecosystems. Acid precipitation will usually consist
of weak solutions (10-3 to 10-5)
and/or nitric acid. From your knowledge of soil chemistry, how would you
expect soil to be affected? What
type of soil
would you expect to be most sensitive?
63. Due to copper's tendency toward passivation, most medieval churches
were roofed with copper, and green roofs have
a dominant feature of the landscape in Europe. After withstanding weather
for hundreds of years, many of
are beginning to leak, as are copper roofs installed since World War II.
What has happened? How might
be related to metal reactions in soils?
64. Soil pollution is becoming
an increasing concern to soil scientists. Modern society not only sees
land as a valid
place to discard
wastes such as municipal sludge, but normal societal activities from food
production to lawn care
add chemicals to the soil. Even beneficial chemicals such as fertilizer
can be a pollutant when added in
quantities. Using a heavy metal such as Cu as an example, explain how and
why this plant nutrient can be a
For any given amount of Cu input, what soil properties or characteristics
will most likely decrease the
65. You decide that it is time
to improve your lawn, so you send a soil sample to the state lab for testing
test is for
exch. K, which is assumed to be a measure of that available). The return
indicates that the soil K level
is very low
and you need to add some of this element to your lawn. Being a college
graduate, you decide to do things
so you set up an experiment in which 0X, 1/2X, 1X, and 2X the amount of
K recommended is added.
you get no response to the added fertilizer. You discuss this with
a family member in another town, and
just the opposite: the soil test indicated adequate amounts of K in the
soil, but the lawn always
to K fertilization. Explain the discrepancy.