Name: ___________________________
AGRONOMY 354
Test 3
October 28, 2015
INDICATE THE ONE BEST RESPONSE. Please cover your answers when not writing.
1.
Lime needs in Iowa:
a) are only significant in the southwest part of the state.
b) would increase as one plowed deeper in northwest Iowa.
c) would be small in areas containing free CaCO3.
d) are usually met by application of Ca(OH)2.
2.
During denitrification, what is the expected end-product of N?
a) N2 b) NO3- c) NH4+ d) R-NH2 e) NH3
3.
The most desirable pH of acid soils in regions of heavy rainfall may be less than the recommended
pH for Iowa soils. Which one of these factors is not a reasonable explanation?
a) high leaching losses of micronutrients
b) different costs of lime
c) less soluble H+ in solution at a given pH in regions of heavy rainfall
d) different clay mineralogy
4.
Most of the nitrogen absorbed by plants is in the nitrate form because the:
a) amine form is strongly held on exchange sites.
b) ammonium form is not usable for most plants.
c) nitrate form is dominant in the soil solution.
d) chitin form is toxic to most plants.
5.
Assume that you have an area near a gravel road where dust from limestone has blown onto the
field. You wish to acidify the soil to grow azaleas and rhododendron flowers. Of those listed, which
material would lower soil pH?
a) Al2(SO4)3 b) CaO c) MgCl2 d) CaSO4 e) KCl
6.
If the C:N ratio of a plant residue is 75:1, one would predict _________ would occur shortly after
adding the residue to soil.
a) nitrification b) mineralization c) denitrification d) immobilization e) volatilization
7.
Salt accumulations in the surface soil horizon are more apt to be observed:
a) immediately following a rain in upland positions of arid regions.
b) in humid regions mainly in depressions one month following a rain.
c) in arid upland positions one month following a rain.
d) in depressional areas in dry climates one month following a rain.
8.
A soil test report calls for 6,000 lbs of ECCE for a 6-inch depth but you wish only to mix the lime into
the surface 4 inches. How much lime is required in pounds?
a) 6,000 b) 2/3 x 6,000 c) 3/2 x 6,000 d) 6/7 x 6,000 e) 7/6 x 6,000
9.
Assuming that 100 pounds of organic nitrogen are released from soil organic matter decomposition
during one year, what is a reasonable estimate of the amount of organic phosphorus released?
a) 90 pounds
b) 19 pounds
c) 9 pounds
d) 0.9 pounds
e) none of these answers is within 5 pounds of expected values.
10.
According to your reading, marl is a naturally occurring material that may be used to
____________________.
a) increase soil pH
b) provide N for specialty crops
c) increase soil acidity
d) provide Fe and Mn for specialty crops
e) provide an organic source of P
11.
"Black alkali" soils are otherwise classified as:
a) high lime. b) saline. c) sodic. d) saline-sodic.
12.
Before spring planting when crop residues such as corn stalks are disked into an Iowa soil,
approximately what percentage of the residues would be expected to decompose during the next 48 weeks?
a) 10% b) 20% c) 50% d) 80% e) 90%
13.
Lime must be added to most Iowa soils to correct unfavorable soil acidity approximately:
a) every 6 months.
b) every 12 months.
c) every 48 months.
d) every 240 months.
e) every year when legume meadow is grown.
14.
Fall application of ammonium fertilizers to benefit spring-planted crops should be delayed until the
soil temperature is below 50 degrees F. Earlier applications are likely to considerably increase
nitrogen losses by:
a) ammonia volatilization.
b) denitrification.
c) erosion.
d) ammonium fixation.
e) leaching.
15.
Identify the true statement concerning biological N2 fixation.
a) only a few animals can accomplish
b) is an energy-releasing process
c) only is accomplished when soil available N is high
d) can only be done by bacteria and actinomycetes
e) must have the active enzyme protected from nitrogen gas
16.
High levels of this ion cause soil aggregate dispersion, reducing aggregation and soil structure.
a) Na b) Ca c) Mg d) K e) Al
17.
According to your reading, residues on the surface of soil provide:
a) for more rapid residue breakdown.
b) for more water in the soil.
c) for high rates of P turnover.
d) for warmer surface temperatures in early spring.
e) lower surface (0-2 inch) levels of organic matter.
18.
A soil contains 0.5% Na2CO3. How much CaSO4·2H2O is required to neutralize this sodium
carbonate in 2 million pounds of soil? (Ca=40, S=32, C=12, Na=23, H=1, O=16)
a) 2 tons b) 4 tons c) 6 tons d) 8 tons e) no value is within 1000 lbs
19.
One of the important reasons for using ground limestone when wanting to raise the pH of an acid
soil is that it:
a) does not harm any kind of plant growth.
b) is the strongest known chemical for this purpose.
c) matches the decomposition rates of soil minerals.
d) supplies Ca and Mg in a mildly alkalizing form.
e) works more rapidly than any other chemical known.
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20.
Most of the high lime soils in Iowa have surface pH values near:
a) 6.4. b) 7.3. c) 8.0. d) 9.1. e) 9.8.
21.
Organic matter builds up in a waterlogged soil because:
a) nitrogen limits decomposition.
b) soils tend to be acid and without oxygen.
c) nitrogen gas is not available for decomposition to occur.
d) mycorrhizae are commonly overactive in a waterlogged soil.
e) phosphorus is lost from this environment, which limits microbial activity.
22.
In the future you accept a position in Sudan. At one location, the soil is unproductive and, on closer
inspection, you determine that the soil accepts water only very slowly. The soil most likely is a
________ soil.
a) high lime b) saline c) saline-sodic d) sodic
23.
Members of the genus Nitrobacter are responsible for:
a) increasing N2 in the soil.
b) loss of available N from the soil.
c) free-living N fixation.
d) fixation of N in association with a plant.
e) converting N to the leachable form NO3-.
24.
Which is likely the best choice for watering your house plants?
a) chlorinated, fluorinated public water supply
b) water through a water softener ("softened water")
c) caught rain water
d) water that contains greater than 2,250 µmhos/cm conductivity
e) no clear choice from above
25.
The best explanation as to why CaSO4 is not a satisfactory liming material is:
a) it is not the salt of a strong base.
b) it is not the salt of a weak base.
c) it is not the salt of a strong acid.
d) it is not the salt of a weak acid.
e) it doesn't contain a satisfactory cation or anion.
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POSSIBLE POINTS ARE INDICATED IN THE LEFT-HAND COLUMN.
26. Describe, in general, the mechanism of how a buffer pH works to determine a soil’s lime
requirement.
(5)
27.
A friend from Ohio is visiting north-central Iowa and notices that soybeans surrounding depressions
tend to have yellow leaves at the top of the plant. You explain this is because the soils have free
calcium carbonate. She asks why the soils in this position on the landscape have free calcium
carbonate. Explain.
(5)
28.
(5)
Describe how Bradyrhizobium in the soil enter a soybean plant and form a nodule.
29.
Explain specifically how the fineness factor for the availability of calcium carbonate is calculated in
Iowa.
(5)
Part 1 _______
Part 2 _______
Total _______
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