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Soil Science > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

Which of the following accurately describes a characteristic of the water molecule?
A. The H to O to H angle is approximately 90o C.
B. The two H atoms are on diametrically opposite ends of the molecule.
C. It has a positive and a negative side.
D. It is attracted to surfaces with negative but not positive charges.
E. It is held in soils by adhesion but not adsorption.

A

It has a positive and a negative side.

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2
Q

Capillarity in soils _____.
A. involves both adhesion and cohesion
B. is enhanced by the symmetrical nature of the water molecule
C. is independent of the matric potential in soils
D. is not involved in the process of water uptake from soils
E. does not account for unsaturated water movement in soils

A

involves both adhesion and cohesion

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3
Q

Two soil samples, A & B, at different soil moisture levels are placed in contact with each other. Water will more likely move from soil A to soil B if their water potentials, expressed in kPa, are:
A. A=-5; B=+5
B. A=-5; B=-5
C. A=-20; B=-10
D. A=-30; B=-40
E. A=-100; B=-50

A

A=-30; B=-40

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4
Q

The osmotic potential would likely be lowest in soils of which of the following orders
A. Aridisols B. Histosols C. Oxisols D. Ultisols E. Spodosols

A

Aridisols

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5
Q

The matric potential of soil water is _____.
A. influenced greatly by the content of salts in the soil
B. not influenced appreciably by the force of gravity
C. is generally higher than that of pure water outside the soil
D. is little affected by soil solids
E. is lower in a sandy soil with 20 percent soil water than in a clay soil with same percentage of moisture

A

not influenced appreciably by the force of gravity

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6
Q

Which of the following best characterizes the field capacity of a soil?
A. maximum capacity of a soil to hold water
B. water content of a soil with water potential of about -10 kPa
C. the total capillary water in a soil
D. a wetted soil prior to the removal of the gravitational water
E. soil with water potential of -1500 kPa

A

water content of a soil with water potential of about -10 kPa

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7
Q

Which of the following means of estimating soil water levels gives a direct measurement of the water content?
A. gypsum blocks B. neutron scattering C. gravimetric determinations
D. tensiometer E. pressure membrane

A

gravimetric determinations

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8
Q

Unsaturated water flow _____________.
A. is faster than saturated flow
B. is driven primarily by the force of gravity
C. is stimulated by the osmotic potential
D. is slower on sands than on clays if the soil moisture content is high
E. occurs on soils that are at field capacity

A

occurs on soils that are at field capacity

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9
Q

In which of the following situations would you expect downward movement of soil water through the profile to be most rapid?
A. uniformly textured sandy loam profile
B. sandy loam in upper layers with a clay band underneath
C. sandy loam in upper layers with a layer of coarse gravel underneath
D. clay texture throughout the profile
E. silt loam in upper layers underlain by a sandy layer

A

uniformly textured sandy loam profile

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10
Q

At which of the following soil moisture potentials (expressed as kPa) is the soil water held most tightly?
A. +5 B. 0 C. -31 D. -1500 E. -3100

A

-3100

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11
Q

At which of the following soil moisture potentials (expressed as kPa) is the waters’ energy level lowest?
A. +5 B. 0 C. -31 D. -1500 E. -3100

A

-3100

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12
Q

Soils high in organic matter commonly hold more available water than comparable soils with lower organic matter levels. This is most likely due to what characteristics of the high O.M. soils
A. larger micro pore space B. lower permanent wilting percentage
C. higher field capacity D. higher capacity of the O.M. to hold water tightly
E. higher clay content

A

higher field capacity

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13
Q

In which of the following “forms” of soil water are pesticides, excess plant nutrients and waste chemicals most apt to move through soils?
A. gravitational B. unsaturated C. available D. hygroscopic E. capillary

A

gravitational

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14
Q

Which of the following statements concerning applications or capabilities of soil moisture measuring devices is (are) true for the use of a drying oven and balance?
A. requires “destructive sampling” for each measurement
B. good to turn on automatic irrigation at -5.0 kPa
C. used to turn on irrigation when soil moisture potential reaches -20.0 kPa
D. gives same reading for loamy sand and silt loam if both contained 15% moisture
E. both A and D

A

Both A/D

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15
Q

The expression, P - ET -SS estimates the ________ a watershed.
A. soil water content of B. discharge volume from C. evaporation from D. interception in

A

discharge volume from

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16
Q

The water potential at the leaf surfaces expressed in kPa is most likely to be _____.
A. -10 B. 33 C. -33 D. -500 E. -31,000

A

-500

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17
Q

Plant transpiration efficiency at a given location is markedly influenced by _____.
A. organic residue cover on the soil B. tillage practices used
C. fertilization practices used D. the plant species being grown
E. both C and D

A

Both C/D

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18
Q

Which of the following will increase the evaporation (E) from the soil surface?
A. adding straw mulch to the soil surface
B. the use of no-till culture
C. stubble mulch farming
D. plastic mulch
E. none of the above

A

E None

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19
Q

Which of the following locations in the United States would have the highest evaporation (E) from the soil surface in July?
A. a bare, unirrigated dry land soil in Colorado
B. an unirrigated soil in South Carolina growing cotton
C. a furrow-irrigated cotton field in Arizona
D. a forest woodland in Illinois
E. a corn field in New York

A

a furrow-irrigated cotton field in Arizona

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20
Q

Urban development of land under natural vegetation or agriculture usually greatly _____ soil infiltration capacity and therefore greatly increases _______.
A. decreases …… stream bank erosion.
B. increases …… stream bank erosion.
C. decreases …… groundwater recharge.
D. increases …….groundwater recharge.

A

decreases …… stream bank erosion.

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21
Q

The likelihood of polluting groundwater with pesticides and plant nutrients is enhanced by _____.
A. the presence of macropores in the soil
B. light tillage of the upper centimeter or so of soil
C. the use of tillage to control weeds
D. the production of oats rather than wheat
E. conventional tillage as a choice compared with conservation tillage

A

the presence of macropores in the soil

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22
Q

Which of the following irrigation systems produces the most biomass per unit of water applied?
A. flood irrigation
B. furrow irrigation
C. drip irrigation
D. sprinkle irrigation
E. furrow-dike irrigation

A

drip irrigation

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23
Q

Groundwater _____.
A. is a source of water above the vadose zone in a soil
B. moves downward in the vadose zone through the capillary fringe
C. moves laterally but not vertically below the soil profile
D. is found mostly in shallow layers just below the argillic
E. is a major source of water for irrigation in the United States

A

is a major source of water for irrigation in the United States

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24
Q

Land drainage is beneficial because _____.
A. it increases the alternate of expansion and contraction due to freezing and thawing of soils
B. it increases the water-to-air ratio in the soil pores
C. it slows down the rate of soil warming in the spring
D. it increases the depth of root penetration in the soil
E. it increases the availability of iron and manganese in acid soils

A

it increases the depth of root penetration in the soil

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25
Q

If you dug a deep hole in your back yard and water started to seep into the hole it would fill the hole up to ________.
A. the infiltration rate B. the percolation rate
C. field capacity D. the water Table
E. the liquid limit

A

the water Table

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26
Q

Where high-value crops or individual ornamental shrubs are to be grown and water is expensive, the most efficient type of irrigation to use would be ______.
A. center pivot B. basin flooding C. furrow D. drip or trickle

A

drip or trickle

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27
Q

Which of the following is not a characteristic of soil colloids?
A. very small size B. high external surfaces
C. electronegative charges D. ability to exchange ions with the soil solution
E. low water holding capacity

A

low water holding capacity

28
Q

If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants, but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5, which of the following would you choose?
A. montmorillonite B. kaolinite C. fine-grained mica D. humus E. chlorite

A

montmorillonite

29
Q

Soils rich in which type of clay would provide the most troublesome site on which to build a home?
A. Fe, Al oxides B. kaolinite C. fine-grained micas D. chlorite E. smectite

A

smectite

30
Q

If you were looking for a soil with high cation exchange capacity and were not concerned with the soil’s physical properties, which of the following would most likely fit your needs?
A. Aridisol B. Oxisol C. Vertisol D. Mollisol E. Ultisol

A

Vertisol

31
Q

The swelling/shrinking tendency of some silicate clay minerals is due primarily to _____.
A. the presence of cations attracted by the negative charges on the internal surfaces
B. the movement of water molecules in and out of the interlayers of the crystal
C. varying thickness of the film of water covering the external surface of the particles
D. expansion in the width of the interlayers due to movement of larger ions such as K+
E. the high Mg2+ contents in the octahedral layers

A

the movement of water molecules in and out of the interlayers of the crystal

32
Q

Which of the following silicate clays would be least apt to be formed from the mere alteration of primary minerals?
A. smectite B. vermiculite C. chlorite
D. fine-grained micas E. iron or aluminum oxides

A

iron or aluminum oxides

33
Q

A well drained soil under a rain forest in Brazil contains significant amounts of a silicate clay. Which of the following is it most apt to be?
A. chlorite B. fine-grained mica C. smectite D. kaolinite E. vermiculite

A

kaolinite

34
Q

As biotite weathers in soils, which of the following would not likely develop by mere alteration of this mineral?
A. fine-grained mica B. kaolinite C. smectite D.chlorite E. vermiculite

A

kaolinite

35
Q

Humus is an important soil colloid. It differs from 2:1 type minerals in all but one of the following characteristics (select the one).
A. structural framework of the particles
B. CEC dependence on soil pH
C. influence of isomorphous substitution
D. capable of adsorbing cations
E. influence on soil aggregate stability

A

D: capable of adsorbing cations

36
Q

Which of the silicate clays would likely have the highest level of potassium in the crystal structure?
A. kaolinite B. chlorite C. smectite
D. fine-grained mica E. vermiculite

A

fine-grained mica

37
Q

True or False: The polarity of water helps account for the attraction of water molecules for each other.

A

True

38
Q

True or False: The hydrogen end of a water molecule is attracted to positively charged cations such as Na+ and Ca2+.

A

False

39
Q

True or False: The property of cohesion in water stems from the attraction of water molecules for soil solids.

A

False

40
Q

True or False: The adsorption of water on soil surfaces encourages capillarity.

A

True

41
Q

True or False: The tenacity with which water is held in soils is directly related to the soil moisture content; the higher the moisture level the greater the attraction of the water to the soil

A

False

42
Q

True or False: Water molecules have polarity primarily because each contains two H atoms and only one O atom.

A

False

43
Q

True or False: The soil water potential is a measure of the potential of a soil to hold water.

A

False

44
Q

True or False: The osmotic potential is dependent upon the presence of salts and other solutes in the soil.

A

True

45
Q

True or False: The matric potential is due to the attraction of water molecules to soil solid surfaces.

A

True

46
Q

True or False: Water will move from one site in a soil with a water potential of -5 kPa to an adjacent site with a water potential of -40 kPa.

A

True

47
Q

True or False: Although the total soil water content of a clay soil is about the same as a nearby well structured silt loam, the clay will likely provide more available water to plants because of its higher abundance of small pores.

A

False

48
Q

True or False: The effect of soil organic matter on the amount of water available to plants is due to organic matter influence on total soil porosity as well as to the water-supplying power of the soil organic matter

A

True

49
Q

True or False: Plant roots gain access to soil water primarily by the growth of the roots into moist soil

A

False

50
Q

True or False: Capillary movement is made possible by the processes of cohesion and adhesion.

A

True

51
Q

True or False: Osmotic and matric potentials are commonly negative because the soil water has a lower energy level than that of pure water.

A

True

52
Q

True or False: Filling the bottom half of a flower pot with gravel will greatly improve the aeration of the soil-mix in the top half

A

False

53
Q

True or False: Early snowfall that arrives before the cold winter weather has frozen the soil generally increases the penetration of water into the soil.

A

True

54
Q

True or False: The water potential in soils is generally considered lower than that in the atmosphere.

A

False

55
Q

True or False: Evaporation from the soil surface (E) is determined to a large degree by soil surface wetness.

A

T

56
Q

True or False: Evapotranspiration includes vapor losses both from the soil surface and from the leaves of plants

A

T

57
Q

True or False: Soil and crop management generally has a greater influence on evaporation from the soil surface (E) than on transpiration (T) from leaf surfaces.

A

T

58
Q

True or False: Vapor loss from a south-facing slope in Australia would likely be higher than from a north-facing slope.

A

F

59
Q

rue or False: Sprinkle irrigation is generally more efficient in the use of water than drip irrigation, especially for high-valued crops.

A

F

60
Q

True or False: Hydraulic redistribution or hydraulic lift dries out shallower soils during dry periods, allowing trees to take advantage of water deeper in the soil profiles.

A

F

61
Q

True or False: Soil colloids are too small to be seen with an ordinary light microscope.

A

T

62
Q

True or False: While kaolinite particles are larger than those of other major silicate clays, the surface area of kaolinite per kilogram is much smaller than that of the 2:1 type minerals like smectite and vermiculite.

A

T

63
Q

True or False: Of the silicate clays, smectite has the least tendency to expand upon wetting and shrink upon drying.

A

F

64
Q

True or False: In most soils of the arid regions of Nevada, smectite is more prominent than in most soils in warm, humid Georgia.

A

T

65
Q

True or False: You would expect the cation exchange capacities of Ultisols to be lower than those of Aridisols if the soil textures are about the same.

A

T

Soil Science (1 decks)

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