Test 2 Flashcards
the bulk of gaseous interchange in soils takes place by ___?
diffusion
a well aerated soil is characterized by a relative abundance of ___?
NO3 ions
Compared to upland soils, weland soils would be characterized by an abundance of ___?
methane
the following is the reduced form of th essential element depicted.
NH4+
The redox potential is a measure of ___?
the tendency of a substance to accept or donate electrons
Soil A has a redox potential of 400mV, soil B -200mV. Of the two soils, soil A is more apt to be characterized by an abundance of ___?
molecular oxygen
the partial pressure of oxygen in the atmosphere is 0.21 bar and that of nitrogen 0.78, Which of the following partial pressure levels would you expect to find in the pores of moderately well drained soil?
.15 oxygen
if you owned a dairy farm with poorly drained clay soils in a humid temperature region which of the following would be most satisfactory from the standpoint of soil aeration and temperature?
ridge till system
which of the following processes are most apt to encourage good soil aeration?
creation of more macropores
forest fires result in sufficiently high soil temperatures to cause vaporization and movement of certain organic compounds in soils. the main effect of these compounds is to ___?
reduce the water infiltration and percolation through the profile
which of the following is considered necessary features for an area to delineated as wetland?
hydric soils
A mineral soil has a water content of 25kg water per 100 kg dry soil. what is the approximate specific heat of this soil, expressed in calories per kilogram
360
the primary characteristic of subsoils that accounts for the ability of a grand circulation heat pumps to moderate temperatures in houses in both summer and winter is
the high specific heat of the soil
Soils rich in which type of clay would provide the most troublesome site on which to build a home?
smectite
If you were looking for a soil with high CEC and were not concerned with the soils physical properties which of the following would most likely fit your needs?
Mollisol
The negative charges associated with semectite clay crystals are due mostly to_____.
isomorphous substitution of Mg for Al in the octahedral sheet
You are working with a soil colloid known to have a reasonably high potassium level a CEC of about 20cmol/kg of clay and little tendency to swell when wetted. Which of the following is it most apt to be the dominant clay material in this soil?
fine-grained mica
Which cation would you expect to be most tightly held in a soil at pH 4.5?
Al+++
If you were seeking a soil colloid with high capacity to adsorb cationic pollutants, but also with a consistent capacity to doso even as the pH varied from 4.0 to 7.5, which of the following would you choose?
montmorillonite
The electronegative charge on 2:1 type silicate clays is due primarily to _____.
Which of the following is NOT a characteristic of soil colloids
low water holding capacity
The swelling/shrinking tendency of some silicate clay amterials is due primarily to
the movement of water molecules in and out of the interlayers of the crystal
Allophane differs from other silicate clays in all ways but one of the following:
the presence of negative charges on the colloidal particles.
Anion exchange by the formation of outer sphere complexes is of least importance in the plant absorption of ____
NO3
A 1 kg soil sample has a 2 cmol of Al+++ on the exchange complex. Addition of which of the following would most effectively replace about half of this Al?
8 mol Ca++
Some soil colloids exhibit positive charges under highly acid conditions. To what are these charges likely due?
protonation of some hydroxyl groups of excess H ions
A well-drained soil under a rain forest in Brzil contains significant amount of silicate clay. Which of the following is it most apt to be?
kaolinite
Which of the following silicate clays would be least apt to be formed from the alteration of primary minerals?
iron or aluminum
Humus is an important soil colloid. It differs from 2:1 type minerals in all but one of the following characteristics.
Capable of adsorbing cations.
Whihc of the silicate clays would likely have the highest level of potassium in the crystal structure?
fine-grained mica
In the B horizon of which order would you most likely find a soil with the highest buffering capacity?
Vertisol
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
What does NOT descrive the role of aluminum hydroxyl ions such as Al(OH)2 in the soil
They are commonly applied to help reduce the soil pH for acid loving plants.
The exchange complexes of strongly acid pH(4.5) mineral soils are saturated mainly with______.
exchangeable Al+++ ions
You are using pure limestone (CaCO3) to provide the Ca needed to exchange with acid cations in a soil with a maximum potential CEC of 20cmol/kg. How many kg of the limestone would you need to add a hectare furrow slice (2,000,000 kg) to reduce the percentage acid saturation from 40 to 10% assuming that all the Ca added exchanged with Al or H ions?
6,000
Which of these essential elements is it most likely to be toxic to plants in a soil at pH 5.0?
manganese
Which of the following trees would expect to fare most poorly in a soil at pH 5.0?
walnut
Phosphorous availability is very low in most strongly acid soils because of its reaction with _____.
iron
Assume you want to grow azaleas in a soil with pH 6.0. The application of which of the following would you use?
elemental sulfur
Under which of the following conditions would you favor a finely ground dolomite limestone as your choice among liming materials?
need to provide magnesium in addition to calcium
In humid regions applications of limestone are repeated every few years primarily because of ______.
An organism that subsists by eating predators would function as a(n) __________ in the soil ecosystem.
tertiary consumer
Which of the following groups of organisms are responsible for greatest amount of organic matter decomposition in soils?
microflora
Which of the following groups is NOT considered to include important primary consumers in the soil ecosystem?
predators
Compared to the bulk soil in which the earthworms live, earthworm casts contain
more of most plant available nutrients
Which group of soil organisms include the largest number of autotroph species
bacteria
In nature, beneficial mycorrhizae form with the roots of _______
grasses, coniferous trees, legumes, broad leaf trees (all of these)
Vesicles and absuscules are structure typically formed ________
none of the above
Members of this (these) microbial group(s) are responsible for a major proportion of the nitrogen fixed globally in symbiosis with higher plants.
actinomycetes and bacteria (a and b)
Disease suppressive soil often results from _____.
proper fumigation with a strong volatile biotoxin, heating the soil by natural solarization or by steam heat, repeated tillage to keep a soil free of living plants for at least one year, and regular additon of a variety of organic material that stimulate diverse microorganisms. (all of the above)
