Soil Color & Its Causes

1. Soil Color & Its Causes

2. Factors that give soil color • Organic matter • Weathered mineral material composing the soil • Quantity and condition of iron present

3. Dark Color in the A Horizon • Usually indicates the presence of organic matter • This is a characteristic of the A horizon

4. 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

5. Basic Color Classifications • Light • Medium • Dark

6. Color 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

7. 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

8. Change in soil color… • Indicates a difference in the soil’s mineral origin (parent material) • Or change in soil development

9. 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.