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Soil Color & Its CausesSoil Color & Its Causes

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Factors that give soil colorFactors that give soil color

1. Organic matter

2. Weathered mineral material composing the soil

3. Quantity and condition of iron present

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Dark Color in the A HorizonDark Color in the A Horizon

• Usually indicates the presence of organic matter

• This is a characteristic of the A horizon

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Sub-soil Color DeterminationSub-soil Color Determination

• Quantity and condition of iron

• Red colors = usually associated with unhydrated iron oxides and indicate a well drained soil

• Yellow colors = largely due to hydrated iron oxides and generally indicate a somewhat more moist condition than red colors

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Basic Color ClassificationsBasic Color Classifications

• Light

• Medium

• Dark

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Color Determination in the fieldColor Determination in the field

• ALWAYS USE MOIST SOIL

• Munsell’s color charts

• Absolute black = 0

• Absolute white = 10

• Light soils hue value = 7 or more

• Medium soils hue value = 5 – 6

• Dark soils hue value = 4 or less

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Munsell Color ChartsMunsell Color Charts

Hue = dominant spectral or “rainbow” color

• Red, Yellow, Blue, Green

Value = relative blackness or whiteness

• Reflected light

Chroma = purity of “color”

• Number increases and the color is more brilliant as grayness decreases

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Change in soil color…Change in soil color…

• Indicates a difference in the soil’s mineral origin (parent material)

• Or change in soil development

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MottlesMottles

• Spots of different colors in the soil

• Generally indicate that the soil has periods of inadequate aeration each year

• Usually rust colored

• Bluish, grayish, & greenish subsoils (gleying) – with or w/o mottles = indicate longer periods each year of waterlogged conditions & inadequate aeration.