What Makes Some Dirt Red in Color?

Some soils are distinctively red in color while others are brown or black. Colour is determined by numerous things, including mineral makeup conditions, weathering and content. Many red lands, such as Georgia’s famous clay, acquire their color by the presence of iron oxides. Gain useful insight into the characteristics of your soil by knowing what its color means.

Soil Color and Drainage

Patterns and color found inside the subsoil offer significant clues to some soil conditions. While soil will be dull and dark well-drained soil is brighter in color. Vibrant red colour results from iron. Waterlogged, anaerobic conditions retard oxidation, leading to dull yellowish-colored or gray soil. Bright red or brownish-red subsoil generally indicates good motion of air and water. Undergo periods of standing water or soils that drain slowly develop mottling that may include both brightly colored brown and red stains mixed with dull gray stripes and spots.

Organic Content

Colour is a good indicator of organic content–the amount of decomposed plant and animal material . Dark brown or black topsoil contains a high proportion of organic matter. Excessively moist soils tend to retard the formation of colours, but don’t necessarily indicate a deficiency of iron. Soil of any color indicates a proportion of organic matter. Wind, sun and water erosion reduce content, leading to soil.

Parent Material

Colour is associated with the parent material from which it was formed. Red soil might be derived from stone, such as the sandstone common into the desert areas of Nevada, California and Arizona. Hematite — that the mineral from which iron ore is obtained — is a frequent source of color for many lands, particularly those in zones or dry areas. Red soil may come and manganese because the stone is broken down through weathering which become oxidized. For instance, the land of the Piedmont region of Georgia was made from deposits of gneiss and white, black and gray granite. Over time, the rock material was reduced to dust, including oxidized iron which colored the soil red.


Occasionally called”red clay lands,” ultisols are among the 12 orders of land, identified by the U. S. Department of Agriculture’s Universal Soil Classification System. Reddish in color, ultisols are located in portions of Africa, Asia and South America and hot, humid areas such as the Southeastern United States. These lands are often highly acidic and form in extremely weathered geologic areas. If correctly amended with lime and fertilizer, ultisols are low in nutrients and contain high amounts of clay but may be utilized for agriculture.

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