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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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Pop Quiz Question: Direction of water flow?

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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 =

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Questions