Soils Up Close: The Soil Profile and Horizon Characteristics.
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Transcript of Soils Up Close: The Soil Profile and Horizon Characteristics.
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Soils Up Close:The Soil Profile and Horizon Characteristics
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I. The Soil Profile
A. Profiles vs. Pedons
Soil Profile: a two-dimensional body, commonly studied in artificial cuts.
Soil Pedon: a three-dimensional body, with the same thickness as a profile, but with a surface area that ranges between 1 and 100 square meters.
From: Birkeland, 1999
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I. The Soil Profile
B. Gaining the 3rd Dimension
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I. The Soil Profile
B. Gaining the 3rd Dimension
1.Roadcut/Construction Excavation
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I. The Soil ProfileB. Gaining the 3rd Dimension2. Pit Excavation
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I. The Soil Profile
B. Gaining the 3rd Dimension
3. Soils Augering
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I. The Soil Profile
C. Major Components of Soil
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I. The Soil Profile
C. Major Components of Soil
Mineral Matter 45%
Organic Matter 05%
Water 25%
Air 25%
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II. Soil Profile Horizons
A. Master Horizons
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I. The Soil ProfileA. Master Horizons……
OAEBCR
Solum
Solum: Consists of the surface and subsoil layers that have undergone the same soil forming conditions.
Epipedon: “over the soil"; the uppermost layer of soil that serves as the diagnostic horizon.
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R
E
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E
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E
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“Zone of Leaching”Or
“Zone of Eluviation”
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Zone of illuviaton
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Diagnostic properties (B horizon)• Thickness
• Color
• Texture
• Structure
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R
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II. The Soil Profile
C. Subhorizons
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Subhorizons
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Subhorizons
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Subhorizons
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Subhorizons
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III. Soil Profile Characteristics
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III. Soil Profile Characteristics
A. Texture
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III. Soil Profile Characteristics
A. Texture
1.Major categories
Boulder
Stones
Cobble
Gravel
Sand
Silt
Clay
600 mm
250 mm
76 mm
2 mm
0.05 mm
0.002 mm
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Texture< 0.002 mm
2.0 to 0.05 mm 0.062 to 0.05 mm
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Texture< 0.002 mm
2.0 to 0.05 mm 0.05 to 0.002 mm
Common in B Horizons
Common in A Horizons
Common in A Horizons over Granites
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work
• Reflects character of Parent Material
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work
• Reflects character of Parent Material
• Affects processes within the soil
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work• Reflects character of Parent Material• Affects processes within the soil
– Degree of horizon development (fine vs. coarse-grained soils)
– Drainage properties– Engineering properties
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work
• Reflects character of Parent Material
• Affects processes within the soil– Degree of horizon development– Drainage properties– Engineering properties– Degree of chemical reactivity– Water retention
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III. Soil Profile Characteristics
A. Texture
2. Importance of Texture in Soils Work
• Reflects character of Parent Material
• Affects processes within the soil– Degree of horizon development– Drainage properties– Engineering properties– Degree of chemical reactivity– Water retention– Erositivity– Tilth
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III. Soil Profile Characteristics
A. Texture
3. Determining Texture
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Qualitative Methods
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Qualitative Methods
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III. Soil Profile Characteristics
A. Texture
3. Determining Texture
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III. Soil Profile Characteristics
A. Texture
3. Determining Texture
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20 ml pipette
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Determine the settling velocity of a clay particle.
Given:Clay = 0.002 mmΡw = 1.00 gm/cm3
ρs = 2.70 gm/cm3
µ = 1.002 * 10-3 (kg/m*s) g = 981 cm/s2
Find V
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Munsell Color Chart
HueValueChroma
III. Soil Profile Characteristics
B. Color 1.Mechanics
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III. Soil Profile Characteristics
B. Color
Hue: Actual color of the soil relative to The primary colors.
7.5 YR is 75% yellow, 25% red
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III. Soil Profile Characteristics
B. Color
Value: Lightness or darkness of color.Value of 8 will be very light, whereasValue of 2 is dark.
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III. Soil Profile Characteristics
B. Color
Chroma: Strength of color, e.g., theamount of pigment in the sample.A chroma of 7 reflects intense color,whereas a chroma of 2 exhibits aweak color.
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Munsell Color Chart
LIGHT/DARK(VALUE)
PIGMENTATION(COLOR)
Hue
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2. The Application of Munsell Colors
a. Good Drainage (Well Drained)•Oxidizing Conditions
Yellow-Brown-Red Colors
Fe 2+ → Fe 3+
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2. The Application of Munsell Colors
a. Good Drainage (Well Drained)
•Oxidizing Conditions
Yellow-Brown-Red Colors
Fe 2+ → Fe 3+
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2. The Application of Munsell Colors
b. Poor Drainage (Reducing Conditions)
Greyish-green-blue Colors
“Gleyed Colors”
Fe 3+ → Fe 2+
Hues > 5Y or “Gleyed Page”
of Munsell Chart
Low Chromas (~1)
“Mottles or Redox Features”
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“Mottles or Redox Features”
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III. Soil Profile Characteristics
C. Structure
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III. Soil Profile Characteristics
C. Structure
1.In General:
•An aggregation of soil particles called peds
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III. Soil Profile Characteristics
C. Structure
2. Significance
•Critical in soil drainage (determines infiltration rates)
•Aeration, root penetration, nutrient retention, tilth
•Related to genesis and rock type
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III. Soil Profile Characteristics
C. Structure
3. Types/Categories
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Sand and Organics
Sand
Soil Drainage Problems
Well drained, well developedsoils in Virginia
Related to alkaline(salty) soils, and/orexpansive clays
Common in A Horizon in VA
A
E,BxKmBq,BmBs
Bt
Bt
Bn
Horizon
Bt
Loose/Granular
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Very FineFine
MediumCoarse
Very Coarse
“Durability”
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Very FineFine
MediumCoarse
Very Coarse
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III. Soil Profile Characteristics
D. Organic Matter
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III. Soil Profile Characteristics
D. Organic Matter
1.What is it, and where is it found?
Underdecomposed plant and animal tissue
Humus (“colloidal soil organic matter that decomposes slowly and colors soils brown or black”) from Birkeland, 1999
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III. Soil Profile Characteristics
D. Organic Matter
1.…..where is it found?
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III. Soil Profile Characteristics
D. Organic Matter
2. Importance
•Increases water holding capacity and tilth
•Increases cation exchange capacity (nutrient holding capacity)
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2. Importance•Increases water holding capacity and tilth•Increases cation exchange capacity (nutrient holding capacity)
•Produces chelating compounds (organic acids) that increase solubility of ions•Releases high amounts of carbon dioxide, which accelerates chemical weathering
– Sources of CO2:--atmosphere (0.03% concentration)
--soils (2 - 25% concentration)
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III. Soil Profile Characteristics
E. Bulk Density
A measure of the weigh of soil per unit volume
Important for studying soil moisture movement rates and rates of clay and carbon accumulation (pedogenesis)
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IV. The Larger View
A.The value of solid profile descriptions (qualitative and quantitative)
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Harden Indices
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