Deck 14: Soil Phosphorus and Potassium

Question 1

In a soil at pH 5.0, most of the inorganic P is likely to be in the form of _______.

A)monocalcium phosphates
B)tricalcium phosphates
C)hydroxy apatites
D)hydrous iron and aluminum phosphates
E)phospholipids

Answer 1

D

Question 2

Non-point source losses of which element are considered to be a serious water pollution problem because the resulting high concentration of the element in stream water is toxic to most fish.

A)potassium
B)phosphorus
C)both a and b
D)neither a nor b

Answer 2

D

Question 3

In acid soils the principal chemical form of phosphorus available for plant uptake is ____.

A)P₂O₅
B)H₂PO₄^-
C)P³⁺
D)HPO₄^2-
E)P^3-

Answer 3

B

Question 4

The total phosphorus lost from various watersheds is most closely correlated with _____.

A)high soil permeability
B)low soil CEC
C)high percentage of forested land
D)extent of artificial drainage
E)high soil erosion

Question 5

The nutrient most often limiting the growth of aquatic plants and algae in unpolluted fresh water lakes is ______.

A)N
B)S
C)P
D)K
E)none of the above

Question 6

Other things being equal, a soil with 30% clay of the ____ type would be expected to have the greatest potassium -fixing capacity.

A)allophanic
B)2:1
C)1:1
D)crystalline iron oxide

Question 7

Compared to the same soil used for cropland, a forested soil would be expected to lose _____ total P to streams draining the watershed.

A)less
B)about the same amount of
C)more

Question 8

Other things being equal, a soil with 30% clay of the ____ type would be expected to have the greatest phosphorus -fixing capacity.

A)allophanic
B)2:1
C)1:1
D)crystalline iron oxide

Question 9

The amount of P lost from agricultural soils by the process(s) of _____ is generally considerably greater than the corresponding losses of potassium.

A)leaching
B)harvest removal
C)gaseous evolution
D)both b and c are correct
E)none of the above are correct

Question 10

In various parts of the world, soil phosphorus is associated with which of the following environmental problems?

A)soil degradation because of depletion of soil phosphorus
B)eutrophication of lakes because of a build-up of soil P in the watersheds
C)toxic levels of phosphate in groundwater supplies
D)both A and B
E)all of the above

Question 11

Loss of P to groundwater is likely to be most significant for which type of soil?

A)highly weathered tropical soils
B)silt loam soils formed in windblown loess
C)cultivated organic peat soils
D)sandy soils under pine forests (Spodosols)
E)calcareous soils

Question 12

In acid soils the principal chemical form of potassium available for plant uptake is ____.

A)K₂O
B)H₂KO₂^-
C)K⁺
D)HKO₂^2-
E)P^-

Question 13

Mycorrhizae improve the nutrition of many plants by ______.

A)transporting phosphorus through the soil to the plant root
B)fixing atmospheric phosphorus into forms readily used by plants
C)masking P-fixation sites on the surface of certain soil minerals
D)readily dissolving iron and aluminum phosphate compounds
E)making the root cell membrane more permeable to phosphate ions

Question 14

In most soils, mineralization of soil organic matter is an important source of plant available ____.

A)potassium
B)phosphorus
C)both A and B
D)none of the above

Question 15

If a manager can afford only a limited amount of soluble P fertilizer for a calcareous soil with low phosphorus availability, the best plant growth is likely to be obtained if the P fertilizer is applied _____.

A)well in advance of the plant's main period of nutrient uptake
B)evenly across the entire area to be fertilized and mixed thoroughly with the soil in the root zone
C)in narrow bands or localized concentrations
D)in combination with ground limestone
E)a combination of both B and D would be best

Question 16

Compared to land that is not disturbed by tillage, conventionally plowed cropland usually loses much more ______.

A)dissolved P
B)particulate P
C)total P
D)both B and C are correct
E)none of the above is correct

Question 17

Approximately what percentage of the P in surface soils is typically found in organic forms?

A)0.1 to 0.5%
B)1 to 5%
C)5 to 15%
D)25 to 75%
E)95 to 98%

Question 18

The sites in certain clay minerals which fix potassium ions are also capable of fixing which other ion?

A)NO₃^-
B)NH₄⁺
C)H₂PO₄^-
D)Ca²⁺
E)H⁺

Question 19

In what range of soil pH is phosphorus generally most available to plants?

A)3.5-4.5
B)4.5-5.5
C)5.5-7.0
D)7.0-8.0
E)>8.0

Question 20

Application of phosphorus fertilizer usually makes plants more susceptible to diseases.

Question 21

The amount of K lost in subsurface drainage waters from humid region forested watersheds is generally far greater than the amount of P lost in this manner.

Question 22

Because of the complimentary ion effect, potassium is more readily leached from an acid soil than from a neutral soil.

Question 23

A soil with a very low equilibrium phosphorus concentration (EPC) is likely to be characterized by a very low potential buffering capacity (PBC).

Question 24

Luxury consumption of potassium most often occurs in coniferous forests growing on low potassium soils where the ecosystem can least afford it.

Question 25

Although only about 2 to 5 percent of the total P in most surface soils is in organic form, this form supplies nearly all the P taken up by plants.

Question 26

Most soils with a high phosphorus fixing capacity are inherently fertile.

Question 27

Eroded sediment usually contains about half as much P per kg as does the soil remaining on the eroded site.

Question 28

Water running off from a bare field whose soil had an EPC of 0.1 mg/L would be expected to be lower in P concentration than runoff from a field whose soil had an EPC of 2 mg/L.

Question 29

The term, eutrophication, comes from the Greek word meaning "to suffocate" and connotes anaerobic decomposition in soils.

Question 30

Deep rooted vegetation such as forest trees can increase the available potassium content of surface soil horizons even though no potassium is added to the soil profile.

Question 31

For soils with significant pH dependent charge, raising the pH with limestone tends to increase the availability of potassium in the soil.

Question 32

For an unfertilized temperate region forested soil with a large amount of interlayer fixed potassium, but a low amount of readily available potassium, the level of readily available potassium is expected to be higher in early spring than in late fall.

Question 33

For optimum growth of herbaceous plants such as cassava, corn, and lettuce, a concentration of at least 1.0 mg/L P should be dissolved in the soil solution.

Question 34

In a soil with a very low potential buffering capacity, the most efficient approach to using potassium fertilizer would be to apply frequent small doses rather than a single large dose.

Question 35

During the last several decades, modern agriculture in the industrialized countries has tended to deplete cropland soils of their supply of available P.

Question 36

Unlike the use of nitrogen fertilizer on forests, the use of potassium fertilizer can be expected to increase the trees' resistance to diseases and/or pests.

Question 37

The fixation of large amounts of potassium from applied fertilizer would reduce the cation exchange capacity of a soil.

Question 38

Annual plants deficient in P usually flower and mature more rapidly than P-sufficient plants.

Question 39

The amount of both P and K fertilizer applied to US farmland has increased dramatically since 1980 as American farmers attempt to maximize profits and meet record demands for food.