characterizing soil horizons physical properties of soils
TRANSCRIPT
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Characterizing Soil HorizonsCharacterizing Soil Horizons
Physical Properties of Soils
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SolidsVoids
AvenuesStorageDistributionMovement
Interactive MediaMineralsOrganic matterReactivity
Idealized Surface Soil
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Parent Material to Soil
Parent Material
Bedrock
Additions
Losses
Translocations
Transformations
Bedrock
Differentiation
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Soil Horizons
Roughly parallel layers in the soil with varying composition and properties
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Criteria for Characterizing Criteria for Characterizing Soil HorizonsSoil Horizons
ColorColor
TextureTexture
DensityDensity
StructureStructure
Organic matterOrganic matter
MineralogyMineralogy
ChemistryChemistry
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Value
Chroma
Hue
Soil ColorSoil Color
dominant spectral color; related to the wavelengthof light. Related to the proportions of red to yellow.
related to total amount of light reflected. measure of the strength
of spectral color
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Hue = 10 YRValue = 6Chroma = 3
Munsell Color 10 YR 6/3
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Physical Criteria for Delineating HorizonsPhysical Criteria for Delineating Horizons
ColorColor
TextureTexture
StructureStructure
DensityDensity
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The Soil Mineral Component: Texture
the size of soil particles
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Soil texture refers to the relative amounts of three distinct sizeseparates comprising the soil
mineral component.
Sand Silt Clay
Sizes classes of particles
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Soil TextureSoil TextureDiameter
Sand (2.0 – 0.05 mm) Quartz
Silt (0.05 – 0.002 mm) Quartz /Feldspars/mica
Clay (<0.002 mm) Secondary minerals
Dominant Minerals
sandsiltclay
100%Quartz Distribution
Class
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Importance of Soil Texture
Soil PorosityParticle Surface Area
(Distribution of particle sizes)
Water/Gas MovementReactivity
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Soil Porosity
Porosity – the total volume of soil pores- the distribution of pore sizes
Sand Silt Clay
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Texture, Pore Sizes, and Water
Large particles yield large pore spacesSmall particles yield small pore spaces
Water moves rapidly and is poorly retained in Coarse-textured sandy soils.
Water moves slowly and is strongly retained inFine-textured, clayey soils.
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Sands
Clays/iron
Rapid
Slow
Water Retained
Poor Retention
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Surface Area and Particle Size
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Each face is 4 mm2 Each face is 1 mm2
6 faces x 4 mm2 = 24 mm2 6 faces x 1mm2 x 8 cubes = 48 mm2
If each of the resulting cubes was divided similarly, the surface area would increase 16 times more
2 mm 2 mm
2 mm
1 mm
1 mm
1 mm
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Surface AreaSurface Area
Specific Surface Area = Surface Area mass
cm2
g
units
Interface with the environment
nutrients
gassesO.M.
water
microorganisms
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Specific Surface Area
Separate SSA (cm2/g)Sand 30Silt 1500Clay 3,000,00016 g of clay
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Soil A
100 g soil
Soil B
95 g sand 4 g silt 1 g clay
90 g sand 5 g silt 5 g clay
95 g sand x 30 g/cm2 = 2850 cm2
4 g silt x 1500 g/cm2 = 6000 cm2
1 g clay x 3 M g/cm2 = 3 M cm2
Total = 3,008,850 cm2
90 g sand x 30 g/cm2 = 2700 cm2
5 g silt x 1500 g/cm2 = 7500 cm2
5 g clay x 3 M g/cm2 = 15 M cm2
Total = 15,010,200 cm2
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Soil Horizons
Texture
Clay Content
Surface Area
Potential Reactivity
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Soil Textural Classes
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Soil Textural Triangle
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Sand <10%Loamy sand 10 – 15%Sandy loam 15 – 20%Sandy clay loam 20 – 35%Sandy clay 35 – 55%Clay > 50%
Florida Soils
clay
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70% sand, 20% silt, 10% clay70% sand, 20% silt, 10% clay
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60% sand, 10% silt, 30% clay60% sand, 10% silt, 30% clay
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Measuring Soil Texture
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Texture-by-Feel
Relative amounts of 3 soil separates:
Sand, Silt, and Clay
Gritty smooth plastic
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Texture-by-FeelSoil
SandNo Ball
Loamy SandNo Ribbon
Grittiness, Smoothness
Low Clay Medium Clay High Clay
Increasing Ribbon Length
Field Analysis
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Texture by Feel
Sand = Gritty
Silt = Smooth
Clay = Sticky, Plastic
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Laboratory Analysis of Soil Texture
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Laboratory AnalysisLaboratory Analysis
Sedimentation – Sand, Silt, and Clay Fraction
gravity
dragdrag
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SandSilt
Clay
SandSilt
Clay
sandsilt
Sedimentation
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Quantifying Sedimentation Rates
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Stokes’ LawStokes’ Law
Velocity V(cm/s) = g (dp-dL) D2
18ų
g = gravitydp = density of the particledL = density of the liquid
ų = viscosity of the liquid
KV = D2
K = 11,241 cm-1 sec-1
1 cm · sec
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Stokes’ LawStokes’ Law
V = K D2
K = 11,241 cm-1 sec-1
Sand: D = 1 mm 0.1 cm
V = 11,241 x (0.1)2
= 112.4 cm/sec
1 cm · sec X cm2
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Stokes’ LawStokes’ Law
V = K D2
K = 11,241 cm-1 sec-1
clay: D = 0.002 mm 0.0002 cm
V = 11,241 x (0.0002)2
= 0.00045 cm/sec
1 cm · sec X cm2
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050
100150200250
300350400
450500
0 0.5 1 1.5 2 2.5
Particle Diameter (mm)
Set
tlin
g V
elo
city
(cm
/sec
)
sandsilt
clay
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SedimentationSedimentation
1 minute Sand settles out
4 hours Silt settles out
sand1 min.silt 4 hr.
suspension
The density of a soil suspension decreasesas particles settle out.
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Stem
Scale
Bulb
weight
t = 0 t = 1 min
Hydrometer MethodHydrometer Method
hydrometer
0 g/L
Pure distilled water (18o C) = 0 g/L
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Hydrometer MethodHydrometer Method
Time = 0 sec density = 40 g/L
Add 40 g soil to 1 liter of water
Time = 1 min. density = 10 g/L
Sand settled = 40 g– 10 g= 30 g
Sand (%) = 30 g sand = 0.75 = 75%
40 g soil
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Time = 4 hrs density = 4 g/L
Hydrometer MethodHydrometer Method
What is being measured?
Clay content = 4 g
Silt % = 100% - (75% + 10%) 100% - 85%
= 15 %
Clay % = 4 g clay = 0.10 = 10% 40 g soil
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Sand = 75%Silt = 15%Clay = 10%
Sandy Loam
Hydrometer MethodHydrometer Method
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Reactivity, Water Movement
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Next: Density, Structure, Porosity