Soil color

Morphological property of soil

Soil color is often the most visually apparent property of soil. While color itself does not influence the behavior or practical use of soils, it does indicate important information about the soil organic matter content, mineralogy, moisture, and drainage. Soil can display a wide range of colors including brown, red, yellow, black, gray, white, and even blue or green, and vary dramatically across landscapes, between the various horizons of a soil profile, and even within a single clod of soil.

Dark brown or black colors typically indicate that the soil has a high organic matter content. Organic matter coats mineral soil particles, which masks or darkens the natural mineral colors. Additionally, soils which accumulate charcoal exhibit a black color.

Red colors often indicate iron accumulation or oxidation in oxygen rich, well aerated soils.

Soil in anaerobic, saturated environments may appear gray or blue in color due to the redox reduction and/or depletion of iron. In an anaerobic soils, microbes reduce iron from the ferric (Fe3+) to the ferrous (Fe2+) form. Manganese may also be reduced from the manganic (Mn4+) to the manganous (Mn2+) form, though iron reduction is more common in soil. Celadonite in hydrothermally altered basalt within the Mojave Desert has been observed to weather into a green colored smectite rich clay soil.

Yellow soils may indicate iron accumulation as well, though in less oxygen rich environments than red soils.

White colors are common in soils with salt, carbonate, or calcite accumulations, which often occur in arid environments.