Mastering 1-3 Flashcards
Soil colloids are, by definition
smaller than 1 or 2 micrometers in diameter
True or False: organic matter has a much higher CEC at pH 5.5 than at pH 8.0
false
If you were attempting to construct a waste-holding pond on sandy soil, you would haul in clayey soil to line the pond bottom to prevent it from leaking. The best kind of clay to use for this purpose would be
smectite
Which of the listed soil colloids has a reasonably high K-level, a CEC of about 20 cmolc/kg, and a low tendency to swell when wetted?
fine-grained mica
Allophane differs from other silicate clays in all ways but one of the following?
the presence of negative charges on the colloidal particles
True or false: A 2:1 silicate clay consists of one octahedral sheet sandwiched between two tetrahedral sheets.
true
True or false: you would expect the cation capacity of Ultisols to be lower than those of Aridisols if the soil textures are about the same.
true
Soils in humid, tropical regions under rain forest are most closely associated with which type of colloid?
Fe and Al oxides
The electronegative charge on 2:1 silicate clays is due primarily to
isomorphic substitution of a central atom for another in the crystal structure of the clay
Soils rich in which type of clay would provide the most troublesome site on which to build a road?
smectite
Which cation would you expect to be most tightly held in soil at pH 4.5?
Al 3+
A black, heavy soil (Vertisol) in Texas (semi-arid climate) contains significant amounts of a silicate clay. Which colloid is most likely present?
smectite
Which of the following is NOT a characteristic of soil colloids?
low water holding capacity
Isomorphous substitution creates net negative charges in clay micelles. A typical example of this process is the substitution of
Mg 2+ for Al 3+ in an octahedral sheet
In cation exchange rxns, hydrated cations adsorbed to the surface of a colloidal particle are replaced by
other hydrated cations
If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants like Cu 2+ but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5, which of the following would you choose?
montmorillonite
If you were seeking a soil colloid with a high capacity to adsorb cationic pollutants like Cu 2+ but also with a consistent capacity to do so even as the pH varied from 4.0 to 7.5, which of the following would you choose?
montmorillonite
In soils, water vapor will move
from areas of warmer to cooler soil
Under unsaturated conditions, water is soil
can become stagnant when the soil texture abruptly changes from fine to coarse
Soils rich in iron oxide are
yellowish-brown or reddish
The bulk of soil-air gas exchange takes place by which process?
diffusion
The difference between the wilting point and field capacity is
known as the available water capacity
What would significantly increase ventilation?
draining the soil of excess water
What is a necessary feature for an area to be delineated as a wetland?
hydric soils
Alternate freezing and thawing of soils result in “heaving” of plants, the destruction of shallow building foundations, and formation of patterned ground. This is caused primarily by what?
the expansion of water when it freezes
Which of the listed sets of soil properties would result in the warmest soil temperature (at 5 cm depth) on a sunny day in early spring in New York state?
albedo = 0.15, water content = 0.15, SW aspect, bare soil surface
The Eh of a soil (pH = 6.5) was reported to be -0.15 volts (-150 mV). This Eh level indicates that
the soil is anaerobic, so that microorganisms are reducing sulfate as electron acceptors instead of oxygen and producing a toxic gas (H2S) that smells like rotten eggs
True or False: Clay soils have smaller pores and hold considerably less water than sandy soils.
False
If the total water potential in the soil around a plant root were –50 kPa, water would move from the soil into the root if the water potential inside the root cells were ___ kPa.
-100
Forest fires result in sufficiently high soil temperatures to cause the vaporization and movement of organic compounds in soil. Which is the main effect of these compounds?
reduce infiltration and percolation
What is not an indicative feature of a waterlogged soil?
the soil has a high clay content
Which of the following is NOT a major factor in determining the aeration status of a soil?
the concentration of nitrogen gas in the soil
In temperate regions, a surface mulch, such as from leaf litter in a forest or crop residues in no-till farming, will cause the soil to be ______ than it would be if bare (unmulched).
warmer in late fall
cooler in early spring
and wetter most of the time
True or False:Poorly drained soils or soils saturated by water tend to be yellowish-brown or reddish.
false
Definition of field capacity?
The percentage of water remaining in a soil 2-3 days after it was saturated and free drainage has ceased.
Ecosystem services provided by wetlands?
storage and filtration of water
storage of carbon
stabilization of regional climate
recreational value
Under saturated conditions,
the flow of water is greater in soil with a greater hydraulic conductivity.
Which is an effective measure to prevent the thaw of permafrost underneath a building?
placing the building on stilts to elevate the building above the ground
The redox potential is a measure of what?
the tendency of a substance to accept of donate electrons
The process of aerobic respiration is a significant source of which of the following gases?
carbon dioxide
The soil horizon in which leached mineral particles such as clay and salts tend to accumulate is the
B horizon
___ weathering alters the internal structure of rock materials
chemical
potassium feldspar weathers in the presence of water containing
carbonic acid
iron weathers through the process of
oxidation
a greenhouse gas called ___ influences the rate of chemical weathering
carbon dioxide
True or False: The greater the depth of water percolation, the greater the depth of weathering and soil development.
true
Soils developing from sand and silt carried by the wind are referred to as
eolian
Which weathering would predominate: a cold, wet environment at high elevation, in which freezing and thawing is common
physical/mechanical
Which weathering would predominate: a cold, dry environment experiencing uplift, in which material is being removed by erosion from an underlying pluton/intrusive igneous rock
physical/mechanical
Which weathering would predominate: a hot, humid climate with heavy precipitation that occurs all year
chemical
Which weathering would predominate: a warm, wet environment with above average yearly rainfall and several stormy seasons each year
chemical
Which weathering would predominate: a hot environment with many short but intense rainstorms
chemical
Which weathers faster granite or basalt?
Basalt
Which weathers faster cracks or no cracks?
cracks
About how long does it take for parent rock to be converted into good soil?
2000–20,000 years
Which of these is NOT an ecosystem service provided by soils.
Large amounts of the greenhouse gases carbon dioxide and methane are locked up in soils.
What is salt weathering?
the formation of minerals in rock cracks during the evaporation of salty water, forcing rock apart
What do freeze-thaw and salt weathering have in common?
Both freeze-thaw and salt weathering require rain and force rocks apart physically.
What do freeze-thaw and salt weathering have in common?
Both freeze-thaw and salt weathering require rain and force rocks apart physically.
True or False: Microorganisms contribute to the formation of soils.
true
The rocky area at the bottom of the photo would be considered which section of a soil profile?
unconsolidated material
The reacttion 2KAISi3O8 + 2H+ + 9H20 → H4Al2Si2O9 + 4H4SiO4 + 2K is an example of
hydrolysis
As an igneous rock weathers in a humid climate, the soil formed has […].
lower concentrations of calcium (Ca) and magnesium (Mg) than did the rock. This is because chemical weathering transfers Ca and Mg ions into the soil solution from where they can be taken up by plant roots or leached into the groundwater.
An important source of acidity in soils that contributes to chemical weathering in soils with circum-neutral pH is
carbonic acid, formed from the interaction of soil water and carbon dioxide produced by the respiration of plant roots and soil microorganisms.
An important source of acidity in soils that contributes to chemical weathering in soils with circum-neutral pH is
carbonic acid, formed from the interaction of soil water and carbon dioxide produced by the respiration of plant roots and soil microorganisms.
When a fire occurs in a prairie, it burns very quickly through the grasses. The soil layer most directly affected in this type of fire will be the __________ horizon.
O
True or False: Eluviation refers to the leaching of minerals and finer soil particles from the upper layers to the lower layers of soil.
true
True or False: soils develop very rapidly, within several years.
false
Under which conditions are the processes of weathering, leaching, and input of organic material from plants into soil maximized?
warm temperatures and abundant water
True or False: An E horizon is more likely to develop in grassland soils than in forest soils.
false
