Soil Fertility Exam 1 Questions

Soil texture class is used to describe groupings of soil particle size with distinct properties and behavior. If Dr. Gan (5ft 2) is a large clay particle, what would a coarse sand particle look like

1 mile

Which of the soil separates has the greatest surface area per gram

Clay

Which texture would have the highest water holding capacity due to the presence of micropores

Clay

Assuming comparable texture, which soil structure would have the greatest permeability

Strong subangular blocky

Kaolinite is a white clay mineral; despite this many soils containing kaolinite are Red to Yellow in color, what causes this color in the soil?

Iron oxides

Pamunkey is the official state soil of Virginia, and it is classified as Fine-loamy, mixed, semiactive, thermic Ultic Hapludalfs. Which soil order does this soil belong to?

Alfisols

Which soil order is most widespread in Virginia

Ultisols

Alfisols and Ultisols differ in what way?

Ultisols generally have lower base saturation in the diagnositc subsoil than Alfisols

Mollisols are productive soils, what vegetation do they commonly form under

Grassland

In clay minerals aluminum forms the basis for which sheet

Octahedral

Which of the following is a 1:1 clay mineral type?

Kaolinite

Isomorphous substitution is an example of what

Permanent charge

During isomorphous subsitution Si4+ in the tetrahedral layer is replaced by which cation?

Al3+

The majority of CEC in kaolinite comes from what source

pH dependent charge

Which is the best weathering order (least weathered to most weathered) for these clay types? (iron/aluminum oxides, 1:1 clays, 2:1 clays)

2:1 clays, 1:1 clays, iron/aluminum oxides

Which mineral below is likely to have the highest CEC?

Vermiculute

A highly weathered, oxide rich soil is limed from pH 4.8 to 6.2. Which chages are most likely

CEC increases and AEC decreases

Fine grained mica is a 2:1 clay mineral, however it does not expand. What holds fine grained mica layers together

Potassium K

Sand and silt have broken edge bonds, why do they contribute relatively little CEC compared with clay

Sand and silt have small surface areas making the negative charges insignificant

Which relationship best describes potential acidity

Exchangeable acidity + residual acidity

Why do ammonium-based nitrogen fertilizers generally acidify soil.

Nitrification of NH3+ produces H+

Following nitrification of ammonium fertilizer, which process most directly cause the loss of base cations from the rooting zone and produces persistent soil acidification

Nitrate leaching with Ca2+ and Mg2+

Which statement best describes the principal action of agricultural lime

Carbonate derived alkalinity nuetralizes H+, which Ca2+ replaces acidic cations on soil surfaces

What is a major benefit of liming a strongly acidic mineral soil

It reduces Al toxicity and improves root growth

A farmer has a hand-held pH meter and measures soil pH in a field A as 4.8 and field B as 5.5. Which field needs more liming to raise pH to 6.5

Can’t decide; need more information

You are helping a corn grower with soil testing in two different fields with similar management histories. Testing results from the Virginia Soil Testing Lab indicate that field A has a buffer index = 5.5, and field B has a buffer index (6.2). Which field needs more money to raise the pH to 6.2

Field A

A soil test report recommends 2.0 tons of pure CaCO3 equivalent per acre. Which statement is correct for a lime product with 80% CCE?

More than 2.0 tons of product per acre is needed

Which soil condition is most directly associated with clay dispersion and poor infiltration

High Exchangeable sodium

Which management strategy is most appropriate for reclaiming a sodic soil

Apply gypsum, provide drainage, and leach the displaced sodium