Soil Science Final Review

Which type of soil structure is typically found in surface soil (A horizons)?

Granular

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

Roots extend into moist soil area. Water flows to the roots by capillarity action.

Which of the following plants would be most apt to tolerate high soil salinity?

Cotton

In which soil order would recent alluvium most likely be a common parent material?

Entisols

T/F: Andisols are found mostly near recently active volcanoes.

True

Humus is an important soil colloid. It differs from 2:1 type minerals in all but one of the following characteristics (select the one).

structural framework of the particles

The water in the soil typically differs from pure water because the soil water

1. contains organic compounds 2. contains mineral nutrients 3. is restrained in its flow by attraction to particle surfaces

After drying to eliminate the water in plant litter, which two elements account for about 80% of the dry weight?

C and O

T/F: While 2:1 type clays have significant internal surfaces, their external surfaces are generally much more extensive.

False

If you want to reclaim a saline soil, which of the following practices would you most likely use?

Leach the soil with water high in calcium and magnesium.

Which of the following is a greenhouse gas contributed to the atmosphere by soils?

Nitrous oxides, carbon dioxide, methane.

T/F: Conservation tillage is not practical in some areas of the Northern part of the United States because the practice lowers the surface soil temperature in the spring of the year.

True

T/F: Early snowfall that arrives before the cold winter weather has frozen the soil generally increases the penetration of water into the soil.

True

significant portion of the global production of methane comes from the activity of termites.

True

Which of the following processes are most apt to encourage good soil aeration?

creation of more macropores

Compared to silt, clay-sized soil particles are characterized by ______.

greater attraction for water

Some irrigation systems have stimulated the formation of saline and saline-sodic soils. What contributes to this process?

inadequate drainage systems to remove soluble salts

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

25 to 75%

Which of the following added to a soil would be likely to result in the greatest level of soil organic matter after several years of decomposition?

5 Mg of carbon in plant roots

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

5.5 - 7.0

In a typical mineral soil in optimal condition for plant growth, approximately what percentage of the pore space would be filled with water and what percentage filled with air?

50% water and 50% air

Green plant residues such as grass clippings or a green manure crop generally have a water content of about ____% by weight.

75

Disease suppressing soil often results from _____.

Adding organic materials to the soil that stimulate diverse microorganisms

The osmotic potential would likely be lowest in soils of which of the following orders.

Aridisols

which of the following horizons has the process of illuviation most likely occurred?

B Horizon

If a dry soil high in certain types of ____ is moistened, it is likely to swell up with enough force to crack pavements and building foundations.

Clay

Which of the following sources of water have the shortest average residence time?

Clouds

The mixed angular gravel, rock, and soil found at the foot of a slope is typical of what type of parent material?

Colluvial

Which type of structure is typically found in sodium-rich sub-surface horizons?

Columnar

Soil detritivores feed principally on ___.

Dead tissue

T/F: A pedon is a 3 dimensional field unit occupying about 1000 square meters (1 hectare) of land area.

False

T/F: All but a few nematodes are pests, attacking either economic or wild plants.

False

T/F: Eutrophication is enhanced by the presence of pesticides in the water draining from agricultural soils.

False

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

False

T/F: Humus has a much higher cation adsorption capacity at pH 5.5 than at pH 8.0.

False

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

False

T/F: Of the silicate clays, smectite has the least tendency to expand upon wetting and shrink upon drying.

False

T/F: On the average, agricultural soils in the US are currently being depleted of their nitrogen supply.

False

T/F: Research has shown that most herbicides and insecticides used in agriculture drastically reduce the numbers of living meso- and microorganisms in soils for several years after the application of these chemicals.

False

T/F: Some 60 percent of the water that is actively involved in the hydrologic cycle worldwide is found in soils.

False

T/F: 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.

False

T/F: The cation capacity of soil humus is two to three times greater than that of an equal volume of high CEC silicate clays.

False

T/F: The cation exchange capacities of alkaline soils are commonly lower than those of comparable soils in humid regions.

False

T/F: The total number of microorganisms in a hectare of soil is far greater than the number of macroorganisms, but the total biomass of macroorganisms in 1 hectare is greater than the total biomass of microorganisms.

False

A homeowner in New Mexico attempted to grow azaleas in a well drained soil (pH 7.5) but the plants were stunted and the leaves were yellow. What is the most likely cause of this constraint?

Fe deficiency

Gypsum is the most widely used chemical for the reclamation of sodic soils. What characteristic likely accounts for this popularity?

Gypsum is abundant and low priced.

Histosols

If the soils are to be used for crop production, for which soil order would land drainage be most critical?

If the average transpiration (T) loss from leaf surfaces in a particular watershed is 10 mm/day, you expect the evaporation (E) from the soil surface to be _____.

Impossible to calculate from the data given

5

In a load of 10 cubic meters of topsoil, approximately how many cubic meters of the volume would be solid material?

Phosphorus availability in acid soils is constrained by the presence of significant quantities of reactive ______.

Iron

The following statements is correct.

Lacustrine parent materials have been subject to weathering for shorter periods of time than residual parent materials nearby.

Biomass consists of ______.

Living organism and cells

An acid soil is known to contain toxic quantities of a certain plant nutrient. Which of these essential elements is it most likely to be?

Manganese

Compared to upland soils, wetland soils would be characterized by an abundance of _____.

Methane

Which of the following groups of organisms are responsible for greatest amount of organic matter decomposition in soils?

Microflora

soil solution

Most of the different nutrients essential for growth are supplied to plants directly from the

A well aerated soil is characterized by a relative abundance of _____.

NO3- (nitrate) ions

Organic matter accumulation is most pronounced in the ____.

O horizon

The addition of large quantities of plant residues to the soil generally ____ the incidence and severity of soil-borne plant diseases.

Reduces

A landscaping contractor wants to change the texture of a silt loam soil to meet the specifications for a loam. S/he would most likely do so by adding ______ to the soil and mixing it well.

Sand

The map units on a detailed soil map in a county soil survey report are most likely to be labeled with names from which category of soil taxonomy?

Series

Which of the categories of soil taxonomy provides the greatest specificity of soil properties?

Series

Texture describes the ____ of particles in a soil.

Sizes

Which of the following pools contain the largest amount of the world's carbon?

Soil

Soils in this order are commonly sandy in texture, quite acidic, and develop primarily under coniferous trees in cool to cold climates.

Spodosols

The amount of different sizes of mineral particles in a soil defines the soil___

Texture

Which of the following is not true with respect to the hydrologic cycle?

There is a net migration of some 40,000 km3 of water in clouds from the land area to the ocean areas.

T/F: In desert areas, the soil under scattered clumps of natural vegetation is usually depleted of nutrients compared to the unvegetated soil between clumps.

True

T/F: Iron and aluminum hydrous oxides are characteristic of soils that are highly weathered chemically.

True

T/F: Leguminous forest trees, such as Locust, enrich the soil in nitrogen, to the benefit of non-nitrogen fixing plants growing nearby.

True

T/F: Leguminous forest trees, such as Locust, enrich the soil in nitrogen, to the benefit of non-nitrogen fixing plants growing nearby. .

True

T/F: Nitrogen fertilization is a significant cause of acidity in many cultivated soils.

True

T/F: Nitrogen taken up by plants growing in a compost-treated soil is indistinguishable from the nitrogen taken up by plants growing in a fertilizer-treated soil.

True

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

True

T/F: Soil colloids are too small to be seen with an ordinary light microscope.

True

T/F: The cation exchange capacity of a soil is determined primarily by the amount and kind of colloids in the soil and by the pH.

True

T/F: The pollution of ground water is often increased by the presence of macropores in soils.

True

T/F: The soils of the world contain more carbon than all the world's vegetation and the entire atmosphere, combined.

True

T/F: Tillage when the soil is too wet is likely to increase the soil bulk density.

True

T/F: Vertisols are characterized by high contents of swelling-type silicate clays.

True

Among the soils of which order would you most likely find the highest buffering capacities?

Vertisol

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?

Vertisol

Cu

Which of the following is (are) essential plant nutrients?

N

Which of the following is considered to be a plant macronutrient?

If you wanted to find a soil where physical weathering dominated over chemical breakdown you would be most apt to find it in ______.

a desert region of Arizona

A soil with a bulk density equal to 0.35 Mg/m3 is most likely what type of soil?

a peat soil

For which substance would the particle density equal the bulk density?

a quartz pebble

A soil pedon is ____.

a three-dimensional unit that embodies the primary characteristics of an individual soil

The presence of rocks such as shale and sandstone indicate the existence of _______.

ancient seas

2.) The sulfur dioxide in the atmosphere ______.

can be an important source of sulfur nutrition for plants, is a major contributor to acid rain, comes from fires such as fossil fuel burning, volcanoes and forest fires.

The process of aerobic respiration is a significant source of which of the following gases?

carbon dioxide

Ultisol in the Congo River basin in Africa

describes a soil likely to contain a significant content of low activity clays?

The exchange complexes of strongly acid (pH 4.5) mineral soils are saturated mainly with _____.

exchangeable Al3+ ions

Plant transpiration efficiency at a given location is markedly influenced by _____.

fertilization practices used and the plant species being grown

A farmer started irrigating a soil some 10 years ago but in recent years yields have declined and the soil physical condition has deteriorated. Which of the following most likely accounts for this situation?

high SAR of the irrigation water

Which of the following characteristics of irrigation water is most apt to stimulate the formation of a sodic soil?

high SAR values

Normal alkaline soils are not characterized by ______.

high levels of exchangeable sodium

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

high soil erosion

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?

higher field capacity

A wildlife biologist in South Africa notes that the soils on south-facing slopes are wetter and deeper than those on north-facing slopes, and therefore support more wildlife. What likely accounts for this difference?

higher soil temperatures on the north slopes

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 ____

if their water potential were expressed in A=-30; B=-40

Increasing the organic matter content of a soil is likely to

increase the soil's water holding capacity

Capillarity in soils _____.

involves both adhesion and cohesion

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

iron deficiency

Brown and red colors in subsurface horizons are caused by __ in the soil.

iron oxides

Which of the following human actions is most apt to result in a long term increase in soil pH?

irrigation with high sodium salt-containing waters

Which of the following is (are) major sources of the carbon dioxide now being added to the atmosphere in excess of the amount taken out by plants?

loss of soil organic matter, burning of fossil fuels, and destruction of natural forests.

Which of the following is not a characteristic of soil colloids?

low water holding capacity

Compared to the bulk soil in which the earthworms live, earthworm casts contain ____.

more of most plant-available nutrients

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

need to provide magnesium in addition to calcium

Which of the following is not a major factor in determining the soil aeration status?

nitrogen gas

The matric potential of soil water is _____.

not influenced appreciably by the force of gravity

Unsaturated water flow _____________.

occurs on soils that are at field capacity

The great majority of nitrogen (95 to 98%) in soils can be found in the form of _____.

organic compounds

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?

oxidation of sulfur-bearing minerals that produces sulfuric acid

Char is made up of _____.

pyrolized plant materials

Which of the following actions would best assure good aeration in a soil?

remove excess water

If you owned a dairy farm with poorly drained clay soils in a humid temperate region which of the following would be most satisfactory from the standpoint of soil aeration and temperature?

ridge-till system

Igneous rocks can best be characterized as

rocks formed when molten magma solidifies

The most common form of on-site waste water treatment for homes not hooked up to sewer lines is the _______.

septic tank and drain field

Fungal hyphae have an important influence on soil structure because they ______.

stabilize macro aggregates

In most soils the overall population (numbers) of microorganisms changes with time, generally following changes in the _____.

supply of decomposable organic matter

Mechanical weathering processes result in:

the disintegration of rocks due to differential expansion of minerals

The likelihood of polluting groundwater with pesticides and plant nutrients is enhanced by _____.

the presence of macropores in the soil

A soil profile consists of

the set of layers seen in a vertical cross section of a soil

Mycorrhizae improve the nutrition of many plants by ______.

transporting phosphorus through the soil to the plant root

Igneous, sedimentary, and metamorphic are three _________.

types of rocks

Which of the following is not considered one of the five major factors influencing soil formation?

valence state

Which of the following best characterizes the field capacity of a soil?

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