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Soils > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Soil texture

A

-relative proportion of primary particles (sand silt clay)

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2
Q

Larger particles are called ______ and have an effective diameter of

A
  • sand
  • 2 - .05mm
  • have irregular size and shape
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3
Q

Smaller particles are called ___ and have an effective diameter of

A
  • clay
  • less than .002 mm
  • colloidal are less than .001 mm
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4
Q

Medium size particles are called ____ and have an effective diameter of

A
  • silt

- .05 - .002mm

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5
Q

Equation for specific surface area

A

=surface area divided by unit mass or volume

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6
Q

Characteristics of sandy soils

A
  • low water holding capacity, organic matter, fertility, and compaction potential
  • rapid water drainage, well aerated
  • susceptible to wind erosion and resist to water erosion
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7
Q

Characteristics of silty soils

A
  • medium water holding capacity, organic matter, fertility, drainage, and aeration
  • ver susceptible to wind and water erosion
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8
Q

Characteristics of clay soils

A

-slow drainage and poor aeration
-high water holding capacity, organic matter, fertility
-if dispersed, susceptible to wind and water erosion
if aggregated, not susceptible to wind and water erosion

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9
Q

Colluvial soil texture _____

Lacustrine soil texture ____

A
  • sand

- clay

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10
Q

Soil structure

A
  • aggregation of primary particles into secondary units

- peds, aggregates

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11
Q

GRADES OF SOIL STRUCTURE
Weak soil structure:
Moderate soil structure:
Strong soil structure:

A

WEAK: poorly formed, indistinct peds, barely observable in place
MOD: well formed peds, evident in undisturbed soil
STRONG: well formed peds distinct in undisturbed soil

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12
Q

Genesis of soil structure: aggregate formation

A

-physical processes
-wetting and drying
freezing and thawing
-physical effects of roots and activity of soil organisms
-long vs short term tillage

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13
Q

Biological processes that enhance aggregate stability

A
  • soil organic matter (SOM)
    - microbial decomposition products
    - root exudates
    - fungal hyphae exudates
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14
Q

Soil structure genesis II, Aggregate STABILITY

A
  • Inorganic material (interacts with organic matter)
  • silicate clay
  • Fe and Al oxides
  • Cations
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15
Q

Site quality

A

-relative measure of the vegetative production capacity of a site for a give purpose

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16
Q

Benefits of soil structure

A
  • INCREASED
    - porosity
    - aeration
    - infiltration
    - percolation
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17
Q

Partical density

A
  • mass per unit volume of soil solids
  • compressed
  • assumed particle density is 2.65 Mg/m^3
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18
Q

Bulk density

A

-mass per unit volume of dry, undisturbed soils
-soil particles plus pore space
=mass (dry) divided by volume

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19
Q

Total pore space =

A
  • soil moisture tension at 0 bars or 0 kPa
  • =100 - ((BD/PD)*100)
  • PD = 2.65
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20
Q

what is the assumed particle density?

A

2.65Mg/m^3

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21
Q

Factors influencing total pore space and bulk density

A
  • STRUCTURE: BD is lower for well developed granular structure
  • ORGANIC MATTER: DB decreases with increasing OM bc there are more small particles, OM contributes to structure
  • DEPTH: DB increases with depth in profile bc there is less freezing/thawing and physical activity
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22
Q

Factors influencing TPS and BD

A

-management practice
-traffic on moist soils = soil compaction
-DB increases with this
-tillage
-DB increases long-term and decreases short term
-long-term is a potential harm
-texture
-DB decreases with finer texture soils so TPS
increases

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23
Q

Hectare furrow slice (HFS)

A
  • 2.2 million kg/HFS
  • 2,000,000 lb/ac (AFS)
  • kg/ha divided by 1.1 = lb/ac
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24
Q

Equation for soil weight

A

-BD x Volume

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25
Q

Ways of measuring bulk density

A

1) core method: V=(pi)h(r^2), BD=m/v
2) clod method: V=displaced water, BD=m/v
3) Excavation: V - with beads, water, urethane foam, BD=m/v
4) Gamma Radiation
5) Freezing: V=water displaced BD=m/v
6) 3D scanning technique

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26
Q

Macropores

A
  • large diameter pores
  • water flows freely if drainage is unimpeded
  • .08 to 5+mm in size
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27
Q

Micropores

A
  • small diameter pores
  • hold water against the force of gravity
  • .03 to .08 diameter
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28
Q

Harvesting impacts of soil structure

A
  • most severe when soils are wet
  • recovery may require freezing
  • poorly sorted sands are most susceptible
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29
Q

Soil physical properties influence soil water:

A

-availability, storage, and movement
-function of pore size distribution and attraction of soil
solids for water

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30
Q

Hydrogen bonding equals high

A
  • boiling pt
  • viscosity
  • specific heat
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31
Q

consequences of polarity

A
  • hydrogen bonding
  • cohesion (water molecule attraction for each other
  • adhesion (water molecule attraction for soil surfaces)
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32
Q

Free energy

A
  • measure of capacity of water to do work
  • water moves from high to low free energy
  • affected by the three sources in the soil
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33
Q

The three little forces affecting free energy

A
  • Matric (attraction of soil solids for water, reduces free energy)
  • Osmotic (attraction of ions for water, reduces free energy)
  • Gravitational (elevation increases free energy)
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34
Q

Total soil water potential

A
  • sum of component potentials

- amnt of work required to transport unit quantity of pure water reversibility and isothermally

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35
Q

Field capactiy

A
  • moisture content of soil 2-3 days after a soaking rain
  • when soil moisture potential is -.1 to -.33 bars
    • or -10 kPa
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36
Q

Wiliting point

A
  • moisture content of soil at which plants wilt

- when soil moisture potential is -15 bars or -1500 kPa

37
Q

1 bar equals ____ kPa

A

100

38
Q

Available water equation

A

=FC-WP

39
Q

Hydroscopic coefficient

A
  • moisture content of air dry soil

- when soil moisture potential is -31 bars or -3100 kPa

40
Q

Gravimetric moisture content

A

=(wet-dry)*100/dry

-percentage

41
Q

Volumetric moisture content

A

gmc x BD

-percentage

42
Q

Factors influencing available water

A
  • texture
  • organic matter
  • thickness
43
Q

soil compaction impacts on available water

A
  • air filled porosity
  • soil structure
  • soil depth/layering
44
Q

Hysteresis

A
  • moisture content of a soil at a given soil water potential

- higher when the soil is drying that when it is wet

45
Q

What does Ksat represent

A
  • saturated hydroulic connectivity
  • pore size/shape/connectivity
  • decreases with time and depth
46
Q

What physical properties result in higher Ksat

A
  • sandy texture

- stable granular structure

47
Q

Preferential flow

A
  • non uniform water movement through soil (macropores)

- free water flows through megapores

48
Q

Unsaturated flow

A
  • driven by gradient in matric potential
  • .001 rate of saturated flow
  • higher for fine texture
49
Q

Well aerated soil

A

-gas exchange sufficiently rapid to replenish oxygen and prevent buildup of carbon dioxide

50
Q

Diffusion

A
  • movement across a gradient in response to a gradient

- 10,000x greater in air filled compared to water filled pore

51
Q

Field soil oxygen availability regulated by

A
  • soil macroporosity texture and structure
  • soil water content air filled porosity
  • oxygen consumption by roots and soil organisms
52
Q

4 methods of assessing soil aeration

A
  • Content of O2 and other gases
  • Air-filled soil porosity
  • Oxygen diffusion rate
  • Redox potential
53
Q

Assesing soil aeration: content of o2 and other gases

A
  • O2 > .1 L/L (10%) required most upland plants

- CO2 > .1 L/L (10%) toxic most upland plants

54
Q

Assesing sol aeration: air filled soil porosity

A

-<20% of TPS or < 10% soil vol

55
Q

Assessing soil aeration: oxygen diffusion rate

A

<0.3 ug/cm^2/min: top growth ceases

<0.2 ug/cm^2/min: root growth ceases

56
Q

Assessing soil aeration: Redox potential (Eh)

A

-tendency of a system to reduce or oxidize

57
Q

IRIS and MIRIS tubes

Ways to measure reduction

A
  • IRIS: indicator of reduction in soils (in Montezuma)

- MIRIS: Mn indicator of reduction in soils

58
Q

Redox potential (Eh) of a well drained soil

A

> .4volts

59
Q

Factors affecting soil aeration

A
  • macropore space
  • biochemical reaction rates
  • season
60
Q

Impact of poor aeration

A
  • reduced root growth
  • reduced root nutrient and water uptake
  • reduced microbial decomposition rate
  • buildup of toxic materials
  • WETLANDS
61
Q

Aeration problems and management alternatives

A
  • improve drainage (ditches, drainage tile, raised beds) to remove water
  • manage for appropriate species
62
Q

Hydric soils

A
  • formed under conditions of saturation, flooding, or ponding long enough during to the growing season to develop anaerobic conditions in the upper part
  • saturated, reduced soils
63
Q

Soil temperature

A
  • affects physical, chemical, and biological soil processes (winter burn)
  • Q10: rate of chemical rx doubles with increase in 10 degrees C
64
Q

Factors influencing soil temperature

A
  • LATITUDE: decreasing NRG input N or S from equator
  • ALTITUDE: decreases 6 deg C per 1000m increase in altitude
  • ASPECT/SLOPE: in the northeast, SW slopes are warmer and drier than NE slopes
  • DEPTH: temp variations cease below 10m depth
  • COVER: ground (living and nonliving)
65
Q

Soil thermal properties

A
  • SPECIFIC HEAT: ratio of the amnt of heat nrg required to raise the temp of a substance 1 degree C compared to that required for the same vol of water
  • HEAT OF VAPORIZATION: amnt of nrg required to vaporize water
66
Q

Heat transfer is soil (Qh)

A

Qh=K(change in T)/x
-K = thermal conductivity
x=distance

67
Q

Thermal conductivty (K) is influenced by:

from heat transfer equation

A
  • soil moisture
  • organic matter content
  • soil texture
  • bulk density
68
Q

Soil temperature and root growth

A
  • minimal range: 0 to 7 deg C
  • optimal range: 10 to 25 deg C
  • Max range: 25 to 35 deg C
69
Q

Frost heaving

A

-formation of segregated ice lenses and volumetric expansion of water during freezing

70
Q

3 requirements of frost heaving

A

1) prolonged period of subfreezing temp
2) frost susceptible soils
3) source of water

71
Q

Accelerated erosion

A

-in response to human activities

72
Q

Geologic erosion

A

-in the absence of human activities

73
Q

Process of soil erosion

A
  • detachment
  • transport (wind, water)
  • Deposition
74
Q

Types of water erosion

A
  • Sheet erosion
  • Rill erosion (miniture gullies)
  • Gully erosion
75
Q

Common models to predict erosion

A
  • WEPP SWAT models

- USLE RUSLE models

76
Q

WEPP

A

-water erosion prediction project
-simulation model that predicts PROCESSES (hydrologic, plant growth, and litter decay), ON AND OFF SITE EFFECTS OF (raindrop impact, splash erosion, etc.)
-soil surface is classified into rill and inter rill
-rill: dG/dx = Di + Dr
-interrill component: Di = KiI^2GeCeSf
Dr = rill detatchment/deposition rate
Di = interrill sediment delivery rate to rills

77
Q

SWAT

A
  • soil and water assessment tool
  • super model comprised of many individual models
  • simulates hydrological processes in large, heterogenous watersheds
  • hillslope erosion (sheet and rill) processes
  • uses modified MUSLE subroutine among other models
78
Q

USLE

A
  • Universal Soil Loss Equation
  • A = RKLSCP
  • R=rainfall erosivity
  • K=soil erodibility
  • LS=topographic factor (slope length (L) x slope gradient (S))
  • C=cover management factor
  • P=support practice factor
79
Q

Vadose zone

A

-zone of aeration above the permanant water table

80
Q

Soil consistence

A

-resistance of a soil to compress under mechanical stress

81
Q

Heat of vaporization

A

-the amount of energy required to turn a liquid into a gas

82
Q

Wind erosion transport mechanics

A

1) SALTATION: short bounces along the ground. 50 to 90% of the movement in wind erosion
2) SOIL CREEP: lateral movement of soil 5 to 25% of total movement
3) SUSPENSION: “dustcloud” particles in the air 15-40% total movement

83
Q

Factors affecting wind erosion

A
  • wind velocity, and turbulence
  • surface roughness
  • soil properties (BD, particle size, moisture of soil)
  • vegetation
84
Q

CRP

A
  • conservation reserve program
  • paying farmers to remove land for production
  • has significantly reduced the amnt of annual soil erosion
85
Q

What is erosion?

A

-the detachment, transport, and deposition of particles

86
Q

Calculation for macropore space

Calculation for micropore space

A

TPS-FC

TPS-macropore

87
Q

how to determine which soil has a finer texture on graph

A

-the one with a greater soil moisture at a given soil moisture tension

88
Q

Difference between mineral soil and organic soil

A

-mineral soil typically have a bulk density greater than 1, organic soils typically have BD much less than 1

Soils (3 decks)

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