Chemical Properties of Red Soil
Red soil is red because of the presence of a particular chemical compound present in them. The mineral iron (chemically represented as Fe) can form two distinct oxides upon reaction with oxygen: ferrous oxide (FeO, one atom of Fe, one of oxygen) and ferric oxide (2 atoms of Fe and 3 of oxygen). Red soil is rich in the purple reddish ferric (Fe203) oxide.
Red soil ie seen as the result of continuous weathering of minerals in a humid climate without new soil formation. The soil is continually lixiviated (washed down) so it is stripped down of minerals and organic matter. The only mineral that survives this lixivation process is the ferric oxide which is highly insoluble in water.
The Food and Agriculture Organization of the United Nations (FAO) has developed a classification system for soil. The World Soil Classification, or World Soil Map, offers a good guide to understanding the various types of soil that exist in the world. Under this classification system, red soil is grouped under the general term of Acrisols
Acrisols are groups of red and yellow colored soil that result from the accumulation of the chemical property, iron oxide (colloquially known as rust) which is highly insoluble in water. Other nutrients such as calcium (Ca) and potassium (K) are usually deficient in acrisols and red soil. Agriculture is difficult (and in some cases almost impossible) in red soil due to the mineral deficiencies of them. Without external supplementation (fertilization), acrisols and red soil (with lime 'minerals' and organic matter and phosphates) are easily exhausted.
The presence of red soil in an area denotes the existence of long processes of weathering and exhaustion. In a sense, red soil can be seen as eroded soil that needs attention and much more soil management so they can be continued to be used properly.