About Lesson
Soil Color
- Soil color doesn’t directly influence soil behavior but indicates composition, mineral content, and environmental conditions.
- It provides clues about drainage, organic matter, and chemical reactions within the soil.
Factors Affecting Soil Color:
a. Organic Matter Content:
- Darker soils = Higher organic matter (e.g., black, dark brown).
b. Mineral Content:
- Iron, manganese, and carbonates influence soil color.
c. Drainage Conditions:
- Well-drained soils = Red/brown; poorly drained = Gray/blue.
d. Climate:
- Arid regions = Light-colored due to salt accumulation.
e. Mineral Composition & Soil Color
|
Mineral |
Formula |
Color |
Soil Condition |
|
Ferric Oxide (Hematite) |
Fe₂O₃ |
Red |
Well-aerated soils |
|
Hydrated Ferric Oxide (Limonite) |
Fe₂O₃·nH₂O |
Yellowish-brown |
Semi-aerated soils |
|
Ferrous Oxide |
FeO |
Bluish-grey |
Poorly drained soils |
|
Manganic Oxide |
MnO₂ |
Blackish-brown |
Oxidized manganese |
|
Manganous Oxide |
MnO |
Bluish |
Poorly aerated soils |
|
Calcium/Magnesium Carbonate |
CaCO₃/MgCO₃ |
White |
Arid regions |
Key Indicators from Soil Color:
- Red color → Iron oxides (Fe₂O₃) under oxidized conditions (good drainage).
- Dark color → High organic matter.
- Yellow color → Hydrated iron oxides (Fe₂O₃·nH₂O).
- Gray/Blue color (Gleying) → Waterlogged soils (FeO presence).
- Mottling → Fluctuating water table (poor drainage).
- Pale yellow with low pH → Acid sulfate soils.
Soil Color Description (Munsell Soil Color System):
Soil color is classified using Munsell Soil Color Charts based on three parameters:
- Hue: Dominant wavelength (e.g., red, yellow).
- Value: Lightness/darkness (higher value = lighter color).
- Chroma: Intensity/purity (low chroma = dull color).