Deck 5: Soil Water: Characteristics and Behavior

Question 1

Which of the following statements concerning applications or capabilities of soil moisture measuring devices is (are) true for the tensiometer?

A) requires "destructive sampling" for each measurement
B) good to turn on automatic irrigation at -50 kPa
C) used to turn on irrigation when soil moisture potential reaches -200 kPa
D) would give the same reading for both a loamy sand and a silt loam if both contained 15%
E) both A and D

Answer 1

B

Question 2

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

Answer 2

A

Question 3

Which of the following statements concerning applications or capabilities of soil moisture measuring devices is (are) true for the electrical resistance block?

A) requires "destructive sampling" for each measurement
B) good to turn on automatic irrigation at -50 kPa
C) used to turn on irrigation when soil moisture potential reaches -200 kPa
D) would give the same reading for both a loamy sand and a silt loam if both contained 15%
E) both A and D

Answer 3

C

Question 4

The following are characteristics of a 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.

Question 5

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

Question 6

Which of the following expressions in kPa is most apt to characterize the gravitational potential of a clay loam surface soil?

A) -5
B) -30
C) 0
D) +5
E) -3100

Question 7

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

Question 8

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

Question 9

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

Question 10

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

Question 11

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

Question 12

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

Question 13

Plant roots obtain access to soil water in which of the following ways?

A) The roots contract and leave room in the pores for the water to move in.
B) Roots extend into moist soil area.
C) Water vapor moves from the wet soil areas to the root surfaces.
D) Water flows to the roots by capillarity.
E) both B and D

Question 14

The water content in a soil is known to be .2 m³/m³ and the potential of pure water outside the system is assumed to be 0. If the soil is a clay loam you would calculate the soil water potential (in kPa) to be

A) 0
B) -5
C) 20
D) -20
E) impossible to calculate with the data given

Question 15

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

Question 16

Which of the following statements concerning applications or capabilities of soil moisture measuring devices is (are) true for the capacitance probe?

A) requires "destructive sampling" for each measurement
B) good to turn on automatic irrigation at -50 kPa
C) used to turn on irrigation when soil moisture potential reaches -200 kPa
D) would give the same reading for both a loamy sand and a silt loam if both contained 15%
E) both A and D

Question 17

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

Question 18

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

Question 19

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

Question 20

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

Question 21

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

Question 22

The soil water potential is a measure of the potential of a soil to hold water.

Question 23

Hysteresis is the phenomenon whereby a soil has the same water content/potential relationship when it is being dried as when it is being wetted.

Question 24

The adsorption of water on soil surfaces encourages capillarity.

Question 25

Filling the bottom half of a flower pot with gravel will greatly improve the aeration of the soil-mix in the top half.

Question 26

Plant roots gain access to soil water primarily by the growth of the roots into moist soil.

Question 27

The matric potential is due to the attraction of water molecules to soil solid surfaces.

Question 28

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

Question 29

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.

Question 30

Capillary movement is made possible by the processes of cohesion and adhesion.

Question 31

The water potential at the field capacity for most soils is in the range of -10 to -30 kPa.

Question 32

Gypsum or nylon electrical resistance blocks are most useful in estimating the soil water content if the soil is quite dry.

Question 33

The property of cohesion in water stems from the attraction of water molecules for soil solids.

Question 34

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 volume of small pores.

Question 35

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

Question 36

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.

Question 37

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

Question 38

The magnetic resonance technique of estimating soil moisture levels can also be used to estimate salt contents.

Question 39

The polarity of water helps account for the attraction of water molecules for each other.

Question 40

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.