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ENST200 > EXAM 2 - Chapters 4 & 5 > Flashcards

EXAM 2 - Chapters 4 & 5 Flashcards

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1
Q

Consistence

A

the ease with which a soil can be reshaped or ruptured; influenced by moisture

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2
Q

Coefficient of Linear Extensibility (COLE)

A

Measures the expansiveness of a soil; the soil is moistened to its plastic limit and molded into a bar that will shrink when air-dried (percent reduction in length of the soil bar)

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3
Q

Plastic Limit

A

the water content corresponding to an arbitrary limit between the plastic and semisolid states of consistency of a soil

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4
Q

Adhesion

A

the attraction of water molecules to other solid surfaces

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5
Q

Plant available water

A

water held with matric potentials between field capacity and the permanent wilting point

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6
Q

What is soil texture determined by?

A

the proportion of particles in different size ranges; sandy loam, silty clay, etc.

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7
Q

What are some biological processes that affect soil structure?

A

Activities of soil organisms, organic matter, tillage, iron/aluminum oxides

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8
Q

How does tillage affect soil structure?

A

it promotes and destroys aggregation; breaks large clods into natural aggregates that allow for root penetration but hasten the oxidative loss of soil organic matter that weakens soil aggregates

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9
Q

Micropores

A

areas filled with water that moves slowly and is not available to plants but acts as hiding places for some adsorbed organic compounds

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10
Q

Percolation

A

the process by which water moves downward in a soil

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11
Q

Wetting Front

A

a sharp boundary between a dry underlying soil and the already wet soil (after an intense rain -> gravity; at a wetting front -> matric)

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12
Q

Matric forces

A

attraction of water to soil solids which reduces the energy state of water near particle surfaces

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13
Q

What pressures are tensiometers useful between?

A

0 and -85 kPa

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14
Q

Wilting coefficient/wilting point/permanent wilting percentage

A

the amount of water retained by the soil when water potential is -1500 kPa

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15
Q

How does pore size affect capillary movement?

A

M/L pores in sandy soils allow for the rapid rise but lesser height; S pores in clay soils allow for the slow rise but greater heights

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16
Q

What is “too dry” in terms of the Least Limiting Water Range?

A

when soil strength exceeds 2000 kPa; in loose well-aggregated soils, this is close to the wilting point

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17
Q

How do soil organisms affect soil structure?

A

Burrowing and molding, the enmeshment of particles by sticky networks of roots and fungal hyphae, production of organic glues by microorganisms

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18
Q

What texture do physical processes affect more? Why?

A

Finer-textured soils (Clays) due to flocculation.

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19
Q

Flocculation

A

the mutual attraction among the clay and organic molecules, the start of aggregation that leads to a clay domain

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20
Q

How does organic matter affect soil structure?

A

soil particles become coated and encrusted during aggregation where they are bound together by interactions with silicate clays, Fe, and aluminum oxides

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21
Q

How do iron and aluminum oxides affect soil structure?

A

large amounts of iron and aluminum oxides coat soil aggregates that prevent breakdown when tilled or wetted

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22
Q

Describe granular soil structure types.

A

Spheroidal aggregates separate from each other in a loosely packed arrangement found usually in A horizons (high in OM); this is the principal type of soil structure affected by management

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23
Q

Describe platy soil structure types.

A

Relatively thin, horizontal sheetlike ped found in both surface and subsurface horizons; developed as a result of soil-forming processes

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24
Q

Describe blocky (sub-angular and angular) soil structure types.

A

irregular cube-like, molded by the shapes of surrounding blocks; angular is where the edges are sharp and the rectangular faces distinct whereas sub-angular is where rounding has occurred; found in B horizons and promotes drainage, aeration, and root penetration

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25
Describe prismatic soil structure types.
Vertically oriented prisms with an angular and flat horizontal structure, commonly associated with swelling clays (Vertisols)
26
Describe columnar soil structure types.
Vertically oriented columns with distinct, rounded tops found in subsoils high in sodium (natric horizons)
27
Microaggregates
particles 2-250 um in diameter comprised of tiny packets of VERY SMALL clay and OM
28
Macroaggregates
particles 0.25-5mm in diameter comprised of microaggregates
29
Macropores
allows for movement of air and drainage of water that accommodates plant roots
30
How do you find Particle Density?
mass solids/volume solids (g/cm^3)
31
What is particle density determined by? What is it not determined by?
Chemical composition and crystal structure; pore space or soil structure
32
How do you find Bulk Density?
mass solids/volume of the whole soil (g/cm^3)
33
What factors affect bulk density?
Soil texture (finer has lower densities because of pores); depth (greater depth = higher Bulk density)
34
How do you calculate % Porosity?
100-(1-(Db/Dp))
35
Plow Pan
a dense zone immediately below a plowed layer formed from compaction by the wheels of heavy machines
36
Surface Seal
a thin, partially cemented, low permeability layer material that inhibits water infiltration and increases erosion losses as a result of separation of aggregates and dilution of salts that clog soil pores
37
Shear Strength
a soils resistance to erosion
38
Proctor Test
- Used to guide efforts at compacting soil materials before construction; measures bulk density - soil is mixed with water and placed in a holder before it is compacted with a hammer to get a curve
39
Plasticity Index
- expansiveness of a soil which indicates the water-content range over which the soil has plastic properties - difference between the plastic limit and liquid limit
40
Describe the relationship of COLE and PI in smectitic soils versus kaolinitic ones?
Smectite clays have high liquid limits and plasticity, especially if saturated with sodium
41
What are the Atterberg Limits?
Shrinkage limit, liquid limit, plastic limit
42
Shrinkage Limit
The water content above which a mass of soil material will swell in volume, but below which it will shrink no further
43
Liquid Limit
The water content corresponding to the arbitrary limit between the liquid and plastic states of consistency of a soil
44
Unified System of Classification
A system used to classify soil materials for engineering uses that groups soils into coarse and fine where coarse grains are then sorted by grain size, amount of fines present and uniformity of grain size while fines are divided into silts, clays, OM, liquid limit, and PI
45
Infiltration
the process by which water enters the soil pore space and becomes soil water; measured using an infiltrometer (double-ring infiltrometer)
46
Cohesion
the attraction of water molecules to each other
47
Osmotic Forces
attraction of water to ions and other solutes that reduce the energy state of water in the soil solution; greater OM the lower osmotic potential
48
Submergence Potential
the positive hydrostatic pressure that occurs below the water table
49
Water Potential
the difference in energy levels between this pure water in the reference state and that of the soil water
50
What does a tensiometer do?
measures the attraction or tension of water; water-filled tube is placed in a porous ceramic cup closed at the top with an air-tight seal where water moves through a cup into the soil until the water potential is the same as the matric water potential, creating a vacuum that can be gauged
51
How do you find gravimetric water content?
mass water/dry soil
52
How do you find volumetric water content?
Db * gravimetric soil water content; compaction increases Ov
53
Field Capacity
the amount of water retained in the soil after all gravitational water has been drained away and gives wat to matric forces
54
Hygroscopic Water
soil water below the permanent wilting percentage that is held by colloidal soil surfaces; atmosphere with 98% relative humidity and equilibrium at -3100 kPa
55
Capillary Mechanism
the movement of water up a substance as a result of the attraction of water to the solid and the surface tension of water (Adhesion and cohesion)
56
What is the formula associated with capillary rise?
H = 0.15/r (cm)
57
Gravitational Water
water in the largest pores
58
Least Limiting Water Range
the range of water contents for which soil conditions do not severely restrict root growth
59
What is "too wet" in terms of the Least Limiting Water Range?
when less than 10% of pores are filled with air that limits root growth due to drowning; in loose, well-aggregated soils, this is close to field capacity
60
What is the effect of compaction on plant available water?
reduces the amount of water plants can take up; crushes macropores and large micropores which decreases the total pore space (Db increases); creation of smaller pores increases the permanent wilting coefficient and decreases available water content
61
What are the related properties of water?
Polarity: due to the alignment of atoms Hydrogen bonding: H atoms of one molecule are attracted to O atoms of another molecule which forms a low energy bond resulting in a high boil point, specific heat, and viscosity of water Hydration: cations become hydrated through O attraction
62
How does packing arrangement affect bulk density?
Loosely packed can result in lower bulk volume while the opposite is true

ENST200 (7 decks)

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