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Exam 9: Soil Acidity

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Question 21

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Which of the following does not describe aluminum hydroxy ions (such as Al(OH) ₂⁺) in the soil?

A) They are more prominent in acid than in neutral soils.
B) They affect the pH of the soil solution through hydrolysis.
C) They block negative sites on some clays thereby reducing the cation exchange capacity.
D) They influence the swelling of some clays by entering into the interlayer spaces.
E) They are commonly applied to help reduce the soil pH for acid-loving plants.

F) B) and E)
G) B) and C)

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Question 22

True/False

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The buildup of excess salts in irrigated soils can result in increased pH if the salts are high in sodium bicarbonate.

A) True
B) False

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Question 23

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If you wanted to quickly increase the pH of a soil to 7.5 to combat a disease in cabbages you are about to plant you should use hydrated lime rather than ground limestone.

Sulfur can be used to increase soil acidity and to reduce alkalinity.

The drainage of certain wetlands has resulted in extreme soil acidity.This is due primarily to which of the following processes that take place when the soil is drained?

Fungi are much more sensitive to strong acid conditions than are bacteria or actinomycetes.

You are using pure limestone (CaCO₃) to provide the calcium needed to exchange with acid cations in a soil with a maximum potential cation exchange capacity of 20 cmol_c/kg.How many kg of this limestone would you need to add to a hectare furrow slice (2.0 x 10⁶ kg) to reduce the percentage acid saturation from 40 to 10%, assuming that all the calcium added exchanged with aluminum or hydrogen ions?

The acidity of "acid rain" can be traced to the reaction of CO₂ in the atmosphere forming carbonic acid (H₂CO₃).

If you want to quickly (in just a few days) increase the pH of a soil from 5.5 to 7.0, which of the following would you use?

Poor plant growth in a well-drained irrigated soil in an arid region (pH=8.0) is most likely due to ________.

Residual soil acidity is that acidity remaining in the soil after limestone has been applied.

When the soil pH = 5.3, manganese is more likely than aluminum to be toxic to plants.

Loblolly pine tolerates higher levels of acidity than beech or maple trees.

The presence of neutral salts in an alkaline soil has a tendency to increase the pH of the soil.

The cation exchange capacity of humus increases if pH increases.

Under which of the following conditions would you favor a finely ground dolomitic limestone as your choice of a liming material?

Hydrogen ions dominate the exchange complex of very acid soils (pH<5).

Which of the following would occur when lime is added to the surface of a soil at pH 6.0?

The amount of limestone required to increase the pH from 5 to 7 would likely be higher for an Oxisol than for an Alfisol.

Bright brownish or reddish colored soil or saprolite layers encountered during excavation are likely to be result in acid sulfate soil problems if exposed to the air.