Soil Color & Its Causes
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Factors 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 Horizon
• Usually indicates the presence of organic
matter
• This is a characteristic of the A horizon
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Sub-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 Classifications
• Light
• Medium
• Dark
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Color Determination in the field
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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 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…
• Indicates a difference in the soil’s mineral
origin (parent material)
• Or change in soil development
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Mottles
• 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.
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