Soil color
Encyclopedia
Soil colour does not affect the behavior and use of soil, however it can indicate the composition of the soil and give clues to the conditions that the soil is subjected to.
Soil can exhibit a wide range of colour; gray, black, white, reds, browns, yellows and under the right conditions green.
Varying horizontal bands of colour in the soil often identify a specific soil horizon
. The development and distribution of color in soil results from chemical and biological weathering, especially redox reactions. As the primary minerals in soil parent material weather, the elements combine into new and colorful compounds. Aerobic conditions produce uniform or gradual color changes, while reducing environments result in disrupted color flow with complex, mottled patterns and points of color concentration.
However the presence of water also affects soil colour by affecting the oxidation rate. Soil that has a high water content will have less air in the soil, specifically less oxygen. In well drained (and therefore oxygen rich soils) red and brown colours caused by oxidation are more common, as opposed to in wet (low oxygen) soils where the soil usually appears grey. This knowledge can be used to form an educated guess about soil drainage in the area.
The presence of specific minerals can also affect soil colour. Manganese oxide causes a black colour, glauconite
makes the soil green, and calcite
can make soil in arid regions appear white.
Soil can exhibit a wide range of colour; gray, black, white, reds, browns, yellows and under the right conditions green.
Varying horizontal bands of colour in the soil often identify a specific soil horizon
Soil horizon
A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...
. The development and distribution of color in soil results from chemical and biological weathering, especially redox reactions. As the primary minerals in soil parent material weather, the elements combine into new and colorful compounds. Aerobic conditions produce uniform or gradual color changes, while reducing environments result in disrupted color flow with complex, mottled patterns and points of color concentration.
Causes of Soil Colour
Soil colour is influenced by the content of organic matter and water as well as the presence and oxidation state of iron and magnesium. Yellow or red soil indicates the presence of iron oxides). Dark brown or black colour in soil indicates that the soil has a high organic matter content. Wet soil will appear darker than dry soil.However the presence of water also affects soil colour by affecting the oxidation rate. Soil that has a high water content will have less air in the soil, specifically less oxygen. In well drained (and therefore oxygen rich soils) red and brown colours caused by oxidation are more common, as opposed to in wet (low oxygen) soils where the soil usually appears grey. This knowledge can be used to form an educated guess about soil drainage in the area.
The presence of specific minerals can also affect soil colour. Manganese oxide causes a black colour, glauconite
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
makes the soil green, and calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
can make soil in arid regions appear white.