Which soil color hue indicates iron oxides and varying drainage?

• A. Gray color
• B. Black color
• C. Red or yellow hues indicate iron oxides and varying drainage
• D. White color

Answer: (C)

Soil color reveals how iron changes state with drainage. Red and yellow hues come from iron oxides like hematite and goethite. These oxides form when the soil is oxidizing, which happens where there is enough drainage for air to enter. When drainage varies—seasonally or with depth—the iron repeatedly oxidizes and sometimes reduces, and the resulting color signals are typically red or yellow, often with mottling as moisture conditions swing. By contrast, gray colors indicate reduced iron under consistently wet, poorly drained conditions; white colors point to leaching or mineral accumulations; black colors come from high organic matter.