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
