Exam 2 Flashcards
What is soil texture?
The distribution of particles into different size classes less than 2 mm and then divided into sand, silt, and clay.
What particle is greater than 2 mm?
coarse fragment or gravel
How large are sand particles?
2-0.05 mm
How large are silt particles?
0.05-0.002 mm
How large are clay particles?
<0.002 mm
What makes a good ribbon?
A soil containing more than 40% clay is sticky enough to form a ribbon
2 inches long or longer.
What makes a fair ribbon?
A soil containing 27-40% clay is sticky enough to form a ribbon at least 1 inch long but not longer than 2 inches.
What makes no ribbon?
The ribbon formed by a
soil containing less
then 27% clay will be
less than 1β long
What does a gritty soil texture tell you?
The individual particles are large enough that one can feel a significant number of particles in a moist soil sample.
What does a smooth or slippery soil texture tell you?
A soil high in silt will feel smooth (lacking the grittiness of sand) or slippery without feeling sticky (a property of clay).
What does a sticky soil texture tell you?
βThe feel of a
moist soil sample
which contains
significant amounts of
clay. Stickiness of clay
allows one to form a
ribbon.
What is the hydrometer method?
Soil particles are dispersed with a sodium meta-phosphate and then agitated. The different soil particle will then settle at different speeds. Smaller particles settle slowly. Larger particles settle fast.
What soil separate has the largest surface area?
a) Gravel
b) Sand
c) Silt
d) Clay
d) clay
What soil separate would have a particle diameter of 0.2 mm?
a) Gravel
b) Sand
c) Silt
d) Clay
b) sand
What is the difference between soil texture and structure?
Texture refers to the sizes of the individual particles that make up the soil (i.e., sand,
silt & clay).
β Structure refers to how these particles may be stuck together to form crumbs or
larger structures.
What is soil structure?
the shape that the soil takes based on its physical and chemical properties.
What is the name of soil aggregates (clumps) that are bound together?
Peds
How does soil structure develop?
Wetting and drying, burrowing of macroorganisms, and Growth of plant roots.
What soil structure is broken into individual particles that do not stick together. Commonly found in sandy soils and C horizons.
Single grained soil structure
What soil structure has no visible structure. Is hard to break apart, appears in very large clods, and is commonly found in the C horizon?
Massive soil structure
What soil structure is thin, flat plates of soil that lie
horizontally, which are usually found in compacted soil?
Platy soil structure.
What soil structure has vertical columns of soil that have a
salt βcapβ at the top and found in soils of arid climates and
generally in the subsoils (B-horizon).
Columnar soil structure
What soil horizon has vertical columns of soil that might
be a few cm long and usually found in B-horizon.
Prismatic Soil structure
What soil structure has Irregular blocks that are usually 1.5 to 5.0 cm in diameter and commonly found in the B-horizon.
Blocky soil structure?
What is Sub-angular Blocky soil structure?
β Like blocky (Irregular blocks that are usually 1.5 to 5.0 cm in diamete) but slightly more rounded. Commonly found in
the B-horizon.
What is Granular soil structure?
Resembles cookie crumbs and is usually less than 0.5 cm in diameter. Commonly found in A-horizons
where roots have been growing.
How does organic matter content change soil?
the stability of the structure will be higher with more SOM
How does fungal hyphae stabilize soil?
Fungal hyphae are
surrounding an
aggregate like a net,
protecting individual
aggregates from
destruction.
What soil structure is common in sandy soils?
a) Granular
b) Columnar
c) Structureless single grain
d) Platy
c) Structureless single grain
What soil structure is commonly found in the A-horizon?
a) Granular
b) Columnar
c) Structureless single grain
d) Platy
a) Granular
What is soil consistency?
The soils resistance to deformation of
rupture, and degree of cohesion and
adhesion.
What are the four stages of soil consistence?
Loose, Friable, Firm, and extremely firm
What is the liquid limit of a soil?
moisture
content at which a
fine-grained soil no
longer flows like a
liquid.
What is the Plastic limit of a soil?
moisture
content at which a
fine-grained soil can no
longer be remolded
without cracking.
What effect does organic matter have on the soilβs color?
It darkens the soil.
What is a matrix color?
The dominant color in the soil
What is Mottling?
Spots or blotches of color in the soil that differ from the matrix color.
What are redoximorphic features?
Mottles that relate to the aeration, drainage, and alterations between aerobic and anaerobic of the soil.
What effect does manganese have on soil color?
Purple black to dark black
What effect does Hematite have on soil color?
Blood red
What effect does Goethite have on soil color?
Yellowish brown
What effect does Hydrated ferric oxide have on soil color?
reddish brown
What effect does carbonates (calcite) have on soil color?
Whitish
What effect does Glauconite have on soil color?
Greenish
What effect does Fe 3 ferric have on soil color?
Red or yellow
What effect does Fe 2 ferrous have on soil color?
Gray to blue
How does the Munell color book work?
Soil color is determined by comparing the color of the soil to the chips in the color charts.
What is soil color consist of?
Hue, Value, and Chroma
What is Hue and how is it shown in the munell color value?
the dominant spectral color of the rainbow - yellow, reds, orange. Shown in the 10YR part of the munell color value.
What is Value?
the relative darkness or lightness of
the soil color. Shown in the numerator of the fraction (5/).
What is Chroma?
Chroma is the relative purity or strength of the color. Intensity or saturation of the hue. Shown in the denominator of the fraction (/5)
What makes dark soils?
decomposed organic matter
What makes yellow soils?
commonly associated
with the presence or absence of iron.
What makes red soils?
Very intense weathering under well-aerated conditions cause formation of the red-colored minerals hematite (Fe2O3). The red soils in NC are also caused by oxidized iron coating around sand particles.
What makes Gray Soils?
Ferrous iron is water soluble and is lost from the soil leaving behind the gray colors primarily associated with silica.
What does Red, yellowish, and gray soil mean for iron?
Lots of iron oxide and well drained (red), some drainage (yellowish), and poorly drained (gray)
What are redox features?
Redox reactions cause fluxuations in the Fe 2 and Fe 3 levels which have different colors associated with them
What makes white subsoil?
White sub-horizons in acidic, sandy soils are often indicative of spodic conditions. Similar features might be present if
there are large accumulations of calcium, sodium or carbonates
The grey color of soil can indicate that the soil has iron and is not well drained.
a) True
b) False
A) True
What is bulk density?
Mass of a volume of undisturbed oven dry soil. Units are g/cm3 or Mg/m3
.
What is the bulk density equation?
π©πππ π«ππππππ = πΎπππππ ππ πΆπππ π«ππ πΊπππ (π) /π½πππππ ππ πΊπππ (πππ)
What is particle density?
The density of solid particles only (solid phase). Units are
g/cm3 or Mg/m3
What is the particle density equation?
π·πππππππ π«ππππππ = πΎπππππ ππ πΆπππ π«ππ πΊπππ (π)/ π½πππππ ππ π·ππππππππ (πππ)
What is porosity?
Total pore space or a measure of the soil volume that holds air and water.
What is the relationship between porosity and bulk density?
they are inversely related
What are macropores?
large pores, water drains rapidly through them due to the force of
gravity.
What are micropores?
small pores, tend to retain water so tightly, its unavailable to plants. Think about capillary action!
What are mesopores?
medium-sized
pores, is the pore space where
you will find plant-available
water. Held tighter than the
force of gravity but not so tight
that plants canβt extract the
water.
What is the porosity equation?
πππππ ππ‘π¦ =(πππ‘π’πππ‘ππ ππππ ππππβπ‘ π β ππ£ππ π·ππ¦ ππππ ππππβπ‘ (π))/ ππππ ππππ’ππ (ππ3)
How can porosity be found with bulk density and particle density?
πππππ ππ‘π¦ = 1 β(π΅π’ππ π·πππ ππ‘π¦ (π/ππ^3)/ππππ‘ππππ π·πππ ππ‘π¦ (π/ππ^3))
What is a normal particle density?
2.65 g/cm^3
Do clay soils or sandy soils have more pore space?
Clay soil because they have smaller and more pores
Compaction will decrease the bulk density of a soil.
a) True
b) False
b) False
As soil bulk density increases, the porosity of the soil increases.
a) True
b) False
b) False
Soil consistence changes with changes in soil water content.
True or False?
True
Conservation tillage can have a significant effect on transpiration of water from a rapidly growing crop of corn.
True or False
False
Structure refers to the shape and size of the aggregates formed by individual particles binding into peds.
True or False
True
Fungal hyphae have an important influence on soil structure because they ________.
A) create large channels that enhance water flow and aeration
B) stabilize macro aggregates
C) help to flocculate the soil colloids
D) are active in the formation of soils crusts
E) all of the above
B) stabilize macro aggregates
Which type of structure is typically found in sodium-rich sub-surface horizons?
A) sub-angular blocky
B) columnar
C) platy
D) granular
E) prismatic
B) columnar
Texture refers to the sizes of the individual particles that make up the soil minerals.
True or False
True
Which of the following is not a textural class name?
A) silt
B) sandy silt
C) clay
D) sand
E) loam
B) sandy silt
Bulk density is constant and does not change as you dig deeper into lower soil horizons.
True or False
False
Soil tilth refers to ________.
A) the moisture content at which a soil is best suited for tillage
B) ratio of bulk density to particle density
C) the bearing strength of a soil under a given downward force
D) the physical suitability of a soil for plant growth
E) micro-aggregates produced as a by-product of tillage
D) the physical suitability of a soil for plant growth
For any soil, the bulk density is always lower than the particle density.
True or False
True
Practices that add organic matter and reduce tillage can be expected to most significantly increase the ________ in a soil.
A) total porosity
B) fineness of texture
C) macropores
D) bulk density
C) macropores
Oxidized (Fe3+) iron-oxides are red whereas reduced (Fe2+) iron-oxides are gray.
True or False
True
Dull gray colors are characterized by ________.
A) low chromas
B) mixed hues
C) high color values
D) gray hues
E) low color values
A) low chromas
The drainage class of a soil (the degree to which the soil becomes water-saturated during the year) can be judged by the presence and location of gray colors in the soil profile.
True or False
True
Tillage when the soil is excessively wet can destroy soil structure, which can increase the soil bulk density.
True or False
True
The plasticity index is used to determine soil texture.
True or False
False
All particles greater than 2.0 mm in diameter are collectively called silt.
True or False
False
Light-colored surface soils are likely to be warmer than dark-colored surface soils if soil moisture and other conditions are the same.
True or False
False
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.
A) iron
B) silt
C) humus
D) clay
E) any of the above
D) clay
Water that plants uptake and then release back into the atmosphere is called:
a) Evaporation
b) Transpiration
c) Evapotranspiration
d) Runoff
b) Transpiration
What is Cohesion?
the attraction of water molecules for
each other primarily due to hydrogen bonding.
What is Adhesion?
the attraction of water molecules for
solid surfaces. Water adsorption to the surface of
soil via H-bonding.
What is capillary movement?
the movement of water up a wick
made of hydrophilic solid materials
The force between two water molecules is called____________, while the force between a water molecule and soil particle is called_____________.
Cohesion, Adhesion
What is gravitational potential?
Potential energy generated by gravity pulling water down.
What is Matric Potential?
Matric potential results from cohesion and adhesion. Causes negative potential (work must be done to extract water)
What is Osmotic Potential?
The greater the concentration of solutes the more negative is the water potential (energy is required). Water moves toward the higher concentration to reach an equilibrium concentration. (is negative)
When the force of gravity is smaller than the force of adhesion, the water will
stay in the soil.
True or False
True
What force results from cohesion and adhesion and is a negative force (i.e., work
must be done to overcome it)?
a) Gravitational
b) Capillary
c) Matric
d) Osmotic
c) Matric
What does it mean if the soil is saturated?
macro, meso and micro-pores
are filled with water.
What is gravitational water?
The water lost from a soil following drainage due to the force of gravity. Water held in the macropores.
What does it mean if the soil is at field capacity?
the amount of water a soil can hold against the pull of gravity. Where gravitational water stops draining.
What does it mean if the soil is at wilting point?
water is held tight as a thin
βfilmβ surrounding soil particlesβ¦ Adhesive
forces are far greater than gravity. The water is held in the micropores.
What does it mean if the soil is at the Hydroscopic coefficient (air-dried)?
Which is soil left out to dry
at room temperature.
What is the water content of different soils at field capacity?
15-25% for sandy soil; 35-45% for loams; 45-50% for clay soils
What is plant-available water?
water between field capacity and permanent wilting point is
plant-available water. The water is held in the mesopores.
What is Unavailable Water?
water between permanent wilting point and oven dry is unavailable
water. The water is held in the micropores and unavailable for plants to use.
How is soil moisture measured using porous block?
The resistance of electrodes embedded in a porous block is proportional to its water content. The wetter a block is, the lower the resistance measured across two embedded electrodes.
How does a tensiometer used to measure soil moisture?
water in the tensiometer leaves through a porous end that air cannot leave through which creates a vacuum
How does a Time Domain Reflectometry (TDR) measure soil moisture?
Measuring the time it takes for an electromagnetic pulse to move a few centimeters in soil. The presence of water in soil affects the speed of the electromagnetic pulse, slowing it down.
What soil texture can hold the most water?
a) Loamy sand
b) Loam
c) Silt loam
d) Silty clay
d) Silty clay
What water freely drains in the soil and is responsible for a lot of the leaching of
nutrients from soil?
a) Gravitational
b) Plant-available
c) Capillary
d) Hydroscopic
a) Gravitational
Wilting point is characterized by:
a) The most amount of water a soil can hold
b) The amount of water available to plants
c) The amount of water tightly held to soil particles
d) The rate at which water moves through the soil
c) The amount of water tightly held to soil particles
What pore size is plant-available water held in?
a) Macropores
b) Mesopores
c) Micropores
d) Cannot be determined with the given information
b) Mesopores
How is soil water content estimated in soil?
a) Single-ring infiltrometer
b) Double-ring infiltrometer
c) Tensiometer
d) Hydrometer
c) Tensiometer
What are three methods for measuring soil moisture?
Time Domain Reflectometry (TDR), tensiometer, porous block
What is the equation for Gravimetric Water Content?
πΊπππ£ππππ‘πππ πππ‘ππ πΆπππ‘πππ‘=(πππ‘ ππππβπ‘ π β ππ£ππ π·ππ¦(π))/ ππ£ππ π·ππ¦ (π)
What is the equation for Saturated Water Content?
πππ‘π’πππ‘ππ πππ‘ππ πΆπππ‘πππ‘ =(πππ‘π’πππ‘ππ π β ππ£ππ π·ππ¦(π))/ ππ£ππ π·ππ¦ (π)
What is the Field Capacity Water Content Equation?
πΉππππ πΆππππππ‘π¦ πππ‘ππ πΆπππ‘πππ‘ =(πΉππππ πΆππππππ‘π¦ π β ππ£ππ π·ππ¦(π))/ ππ£ππ π·ππ¦ (π)
What is the Wilting Point Water Content equation?
ππππ‘πππ πππππ‘ πππ‘ππ πΆπππ‘πππ‘ = (ππππ‘πππ πππππ‘ π β ππ£ππ π·ππ¦(π))/ ππ£ππ π·ππ¦ (π)
What is the Hygroscopic (air dry) water content?
π»π¦ππππ πππππ πππ‘ππ πΆπππ‘πππ‘ =
(π΄ππ π·ππ¦ π β ππ£ππ π·ππ¦(π))/
ππ£ππ π·ππ¦ (π)
What is the equation for gravitational water content?
πΊπππ£ππ‘ππ‘πππππ πππ‘ππ πΆπππ‘πππ‘ =
(πππ‘π’πππ‘ππ π β πΉππππ πΆππππππ‘π¦ (π))/ ππ£ππ π·ππ¦ (π)
What is the Plant-Available Water Content equation?
πππππ‘π΄π£πππππππ πππ‘ππ πΆπππ‘πππ‘ =
(πΉππππ πΆππππππ‘π¦ π β ππππ‘πππ πππππ‘ (π))/ ππ£ππ π·ππ¦ (π)
What is the equation for Unavailable Water Content?
ππππ£πππππππ πππ‘ππ πΆπππ‘πππ‘ =
(ππππ‘πππ πππππ‘ π β ππ£ππ π·ππ¦ (π))/ ππ£ππ π·ππ¦ (π)
What are the two ways to calculate Volumetric water content?
VWC = GWC x Bulk Density
ππππ’πππ‘πππ πππ‘ππ πΆπππ‘πππ‘ =
(πππ‘ ππππβπ‘ π β ππ£ππ π·ππ¦(π))/ πππ‘ππ ππππ’ππ (ππ3)
How do you calculate depth of water?
Depth of Soil x VWC = Depth of Water
What soil will infiltrate the greatest amount of water?
a) Beach sand
b) A silt loam soil under potato production
c) A loam soil under frosted conditions
d) A compacted clay soil
a) Beach sand
A soil has a platy texture, lots of micropores, and has a slow infiltration rate. What is
the soil texture?
a) Sandy
b) Silty
c) Loamy
d) Clayey
d) Clayey
Drainage systems are designed to increase gas exchange between the soil and
atmosphere, so the soil can get more CO2
True or False
False
What are the two categories of erosion?
Geological (not humans) and human-accelerated erosion
What is the three step process for erosion?
- Detachment
- Transport
- Deposition
What are the three types of erosion?
Sheet erosion, Rill erosion, and Gully erosion
What is Sheet erosion?
Uniform erosion from
the entire soil surface
following detachment
due to raindrops
What is Rill erosion?
The removal of soil by
concentrated water running
through little streamlets.
Rills are less than 4 inches
deep, are can be repaired
by tillage or minimal land
leveling.
What is Gully erosion?
Channels deeper than 18
inches that cannot be
erased by cultivation or
simple land leveling
What soil particle size is the most easily eroded?
a) Gravel
b) Sand
c) Silt
d) Clay
c) Silt
What is the Universal Soil-loss Equation?
π΄πππ’ππ π πππ πππ π πππ ππππ = π
Γ πΎ Γ πΏπ Γ πΆ Γ π
* R = rainfall and runoff factor
* K = soil erodibility factor
* LS = slope and length factor of area
* C = cover/vegetation and management factor
* P = practices put in place to prevent erosion
What are the 5 factors in the Universal Soil-loss Equation?
R = rainfall and runoff factor
* K = soil erodibility factor
* LS = slope and length factor of area
* C = cover/vegetation and management factor
* P = practices put in place to prevent erosion
What is the Wind Erosion Prediction Equation?
π΄πππ’ππ π πππ πππ π πππ ππππ = π πΌ Γ πΆ Γ πΎ Γ πΏ Γ π
β I = soil erodibility
β C = climate
β K = soil-ridge-roughness
β L = field width
β V= vegetative cover
What are the 5 factors in the Wind Erosion Prediction Equation?
β I = soil erodibility
β C = climate
β K = soil-ridge-roughness
β L = field width
β V= vegetative cover
Wind erosion is generally not affected by:
a) Soil pH
b) Soil texture
c) Soil moisture
d) Soil crusting
a) Soil pH
The matric potential is due to the attraction of water molecules to soil solid surfaces.
True or False
True
Which of the following means of estimating soil water levels gives a direct measurement of the water content?
A) neutron scattering
B) gravimetric determinations
C) gypsum blocks
D) tensiometer
E) pressure membrane
B) gravimetric determinations
The tenacity with which water is held in soils is directly related to the soil moisture content, the higher the moisture level the greater the attraction of the water to the soil.
True or False
False
Which of the following sources of water have the shortest average residence time?
A) clouds
B) oceans and ice caps
C) soil moisture
D) groundwater
A) clouds
Where high-value crops or individual ornamental shrubs are to be grown and water is expensive, the most efficient type of irrigation to use would be ________.
A) furrow
B) center pivot
C) basin flooding
D) drip or trickle
D) drip or trickle
The osmotic potential would likely be lowest in soils of which of the following orders?
Question 6Select one:
A. Ultisols
B. Histosols
C. Oxisols
D. Spodosols
E. Aridisols
E. Aridisols
Which of the following processes are most apt to encourage good soil aeration?
A. reaction of oxygen with organic matter
B. diffusion of oxygen from the soil to the atmosphere
C. organic matter decomposition
D. creation of more macropores
E. root respiration
D. creation of more macropores
Evaporation from a south-facing slope in Russia would likely be higher than from a north-facing slope.
True or False
True
Land drainage is beneficial because ________.
A. it increases the availability of iron and manganese in acid soils
B. it slows down the rate of soil warming in the spring
C. it increases the water-to-air ratio in the soil pores
D. it increases the depth of root penetration in the soil
E. it increases the alternate of expansion and contraction due to freezing and thawing of soils
D. it increases the depth of root penetration in the soil
At the soil moisture status βair dry,β water can easily be extracted by plants.
True or False
False
βLivingβ terraces involving rows of deep rooted grasses planted on the contour would be considered as contributing to which factor in the Universal soil-loss equation?
L, K, P, S, or R
P
Wind erosion accounts for about what percent of the total soil erosion losses in the United States?
A. 5%
B. 20%
C. 10%
D. 75%
E. 35%
E. 35%
The key to preventing soil erosion by water on both farmland and landscaping job sites is ________.
A. to grade or till the soil until a smooth surface is achieved
B. to keep the soil surface covered with vegetation
C. to keep the soil moist (with irrigation if necessary)
D. to practice good landscape sanitation by clearing away any weeds and old plant residues
E. to provide adequate surface and subsurface drainage
B. to keep the soil surface covered with vegetation
The universal soil-loss equation (USLE) suggests that soil erosion loss is a product of all but one of the following factors ________.
A. sloped steepness
B. soil drainage
C. vegetative cover
D. climate
E. slope length
B. soil drainage
The P factor in the Universal soil-loss equation is concerned with all but one of the following ________.
A. contour tillage
B. soil erodibility
C. strip-cropping
D. terraces
E. vegetative covers
B. soil erodibility
Which of the following statements about soil erosion is not true?
A. Soil erosion losses per hectare of cropped land are higher in Asia and Africa than the United States.
B. Soil erosion losses of potassium exceed those of nitrogen and phosphorus.
C. Downstream off-site costs of erosion are often higher than those in upstream fields from which the soil came.
D. The rate of soil erosion loss in the United States declined from 1980 to 1995.
E. Less than 20 percent of the total soil erosion in the United States comes from croplands.
E. Less than 20 percent of the total soil erosion in the United States comes from croplands.
Conservation tillage systems are said to have all of the following advantages but one over conventional tillage systems ________.
A. it encourages higher microbial population numbers in the soil
B. it involves the use of less toxic weed control practices
C. it increases the hydraulic conductivity of the soil
D. its labor and energy requirements are lower
E. it reduces soil erosion
B. it involves the use of less toxic weed control practices
The R factor of the Universal soil-loss equation is concerned with ________.
A. climate
B. residue cover on the soil
C. terraces
D. soil erodibility
E. slope steepness
A. climate
A soil has been managed using a no-till system for 10 years following many years of conventional tillage operations. Which of the following changes in surface soil properties would you expect due to the no-till management system?
A. The earthworm population would decline.
B. Organic matter content would increase.
C. Bulk density would increase.
D. Soil pH would increase.
E. Aggregate stability would decline.
B. Organic matter content would increase.
