Soils of the humid tropical and equatorial zones are called latosols, or lateritic soils. They are characterized as follows:
(1) Chemical and mechanical decomposition of the parent rock is complete, owing to the favorable conditions of moisture and heat.
(2) Silica has been almost entirely leached from the soil.
(3) Sesquioxides of iron and aluminium have accumulated in the soil as abundant and permanent residual materials.
(4) Humus is almost or entirely lacking because of the rapidity of bacterial action in the prevailingly warm temperatures.
(5) The soil is distinctively reddish because of the presence of sesquioxides of iron.
The silicate clay minerals render the latosols relatively low in plasticity (stickiness) and remarkably porous. Consequently rainfall sinks readily into these soils.
True latosols are found only in warm, humid regions and, hence, correspond closely with the wet equatorial climate and the tropical wet-dry climate. Though the red-yellow podzolic soils show the effects of laterization, they are not to be classified as true latosols.
Latosols quickly lose their fertility under crop cultivation because excessive leaching has removed the plant nutrients in all but a thin surface layer. However, the soil is favorable for the luxuriant growth of broadleaf evergreen rainforest. Other large areas have the raingreen forest and woodland associated with the tropical wet-dry climatic regime.
An interesting feature of latosols is the local development of accumulations of iron and aluminium sesquioxides into layers that can be cut out as building bricks. The material is termed laterite. On exposure to the drying effects of the air, these blocks become very hard.
Valuable mineral deposits occur as laterites. These are thick layers of such minerals as bauxite (hydrous aluminium oxide), limonite (hydrous iron oxide), and manganite (manganese oxide). They are known as residual ores because they are not soluble in soil water and have continued to accumulate as the parent rock has weathered away and the silica and other soluble constituents have been removed. Important bauxite deposits of the Guianas of northern South America and western India are of this type. Valuable resources of manganese are in laterite deposits.
Variations of the latosols have been described as yellowish-brown lateriatic and reddish-brown lateriatic soils. Large upland areas of Africa and India within the tropical wet-dry climate regime have black and dark gray tropical soils. These dark soils may be related to special conditions of underlying bedrock. For example, the dark soils of peninsular India coincide rather well with the Deccan Plateau, underlain by basalts.
"The world is a book, and those who do not travel read only a page", St. Augustine said. Here at www.travel-university.org we believe that every page must be read and explored. Travel is an avenue of learning that no text or classroom can teach. The world is a living classroom and you the student. We invite you to the www.travel-university.org library where you can read general interest and detail oriented articles.
