1 Important/significant foundation soil physical properties Color Redoximorphic features Texture...
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Transcript of 1 Important/significant foundation soil physical properties Color Redoximorphic features Texture...
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Important/significant foundation soil physical properties
ColorRedoximorphic features Texture StructureConsistence Coarse fragments Reaction
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Important/significant foundation soil physical properties
• Color – not an influence, but an indicator and diagnostic resource
• Texture – the composition (sand, silt, clay), the feel, the classification (triangle) - micropores
• Structure – how the particles are aggregated, bound together – macropores
• Consistence – how the soil holds together, feels, can be worked when wet; assessing texture
• Coarse fragments – rocks don’t hold water!• Soil reaction – acid or base, leached or not
leached, saturated or not saturated
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• Color reflects physical, chemical and/or biological composition and processes
• Dark brown-black = organic matter• Bright-light = leached or bleached zones• Subsoil color reflects parent material• Subsoil color reflects redox status
oxidation = aerated
reduction = anaerobic, lacking oxygen
Carbonates, sulfates, chlorides affect color
Mottles, speckles, blotches – alternating wet and dry conditions.
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Soil color as a diagnostic tool Color reflects the parent material, the soil formation
process, and the hydraulic properties of the soil
• There are two ways to ‘look at’ soil color – • 1) as a diagnostic tool – what happened!• 2) as a characterization/classification tool –
what will happen!
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Soil Color
Coloring agents in the soil Effect/expression of
Organic matter darkens the soil
Iron (Fe):primary coloring agent in the subsoil
orange brown colors associated with well drained soils are the result of Fe oxide stains coating individual particles.
Manganese (Mn) is common in some soils
very dark black or purplish black color
Matrix color the dominant color in the soil
Mottling spots or blotches of color in the soil that differ from the matrix color
Redoximorphic features mottles that relate to the aeration, drainage, and alterations between aerobic and anaerobic of the soil
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Redoximorphic featuresmottles that relate to the aeration and drainage status of the soil, and alterations between aerobic and anaerobic conditions of the soil
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A B C D
Deal or No Deal!
As a generalization – soils of fine, very uniform texture and very limited particle size distribution often have ‘internal drainage’ limitations.
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Alisol – poorly drained clay loam soil due to dense sub-surface
horizon rich in clay and aluminum
Poorly drained silty clay loam derived from alluvial deposits on a modern-day
flood plain
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Deep, poorly drained fine sandy loam formed in
sandy marine deposits, flood-plains and depressions.
Shallow water table
Moderately well drained, slow permeability, deep to water
table. Smectite clay; highshrink-swell properties
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Soil colors associated with soil attributes.
Soil color Soil attributes
Environmental conditions
Brown to black (surface horizon)
accumulation of organic matter (OM), humus
low temperature, high annual precipitation amounts, soils high in soil moisture, and/or litter from coniferous trees favor an accumulation of OM
Black (subsurface horizon)
Accumulation of manganeseParent material (e.g. basalt)
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Bright-light- nearly white
Elluvial horizon (E horizon)
In environments where precipitation > evapotranspiration there is leaching of sequioxides, carbonates, and silicate clays. The elluviated horizon consists mainly of silica
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Brown to black (surface horizon); surface well-drained, good aeration. Darker vertical soil deposits are remnants of burrowing animals.
The technical term is krotovina (crotovina): an animal burrow that has been filled with organic or mineral material from another soil horizon.
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Reddish brown subsoil, suggesting good drainage, aeration. Note the buried A horizon, with additional subsoil material above – suggesting colluvial deposition or some form of mass action in recent past. Zone of elluviation below the buried A horizon
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Bright-light; eluvial zonebelow the relatively shallow organic horizon near surface; the light-colored soils, the abundanceof red and yellow suggesta well-drained soil. Consider-ing that elluviation has also occurred, one would concludethat this would be a suitablesite – good internal drainage,appears to have good waterholding capacity.
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Redox – reduction-oxidation status• Reduction – oxygen is
depleted from the soil, the soil may be anaerobic, iron and manganese chemistry change, resulting in color changes.
• Mottles/Gleying• Oxidation – oxygen is
present in the soil, the soil is aerobic, leaching is likely occurring, light color of soil.
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Yellow to reddish
Fe3+ (oxidized iron)
Well-aerated soils
Gray, bluish-green
Fe2+ (reduced iron)
Poorly drained soils (e.g. subsurface layer with a high bulk density causes waterlogging, or a very fine textured soil where permeability is very low), anaerobic environmental conditions
White to gray
Accumulation of salts
In arid or subhumid environments where the evapotranspiration > precipitation there is an upward movement of water and soluble salts in the soil
White to gray
Parent material: marl, quartz
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An explanation of the Munsell color wheel and Munsell color charts
Hue: It is the dominant spectral color, i.e., whether the hue is pure color such as yellow, red, green, or a mixture of pure colors.
Value: It describes the degree of lightness or brightness of the hue reflected in the property of the gray color that is being added to the hue.
Chroma: It is the amount of a particular hue added to a gray or the relative purity of the hue.
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Standardizing Color – the Munsell Color Chart
• Munsell Color System • Hue refers to the dominant
wavelength of light (color) (red, yellow, green, etc.).
• Value refers to the lightness and darkness of a color in relation to a neutral gray scale.
• Chroma is the relative purity or strength of the Hue.
• Notation
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Hue = 5YR
Value = 2.5 – 8
Chroma = 1-8
So, for example: a soil horizon with a Munsell color description of 5YR 5/4 =