Geography – Soils in hot arid and hot semi-arid environments | e-Consult

Laterite soils are characteristic of tropical areas with alternating wet and dry seasons. Their formation is a result of intense chemical weathering of parent material, typically volcanic or sedimentary rocks, under high temperatures and rainfall. The key processes involved are:

• Intense Chemical Weathering: High temperatures and alternating wet and dry periods lead to significant chemical breakdown of the parent rock. This is particularly effective in dissolving soluble minerals like feldspar and silica.
• Leaching: Heavy rainfall leaches out soluble minerals, leaving behind insoluble residues. This process is crucial for the accumulation of iron and aluminium oxides.
• Oxidation: The presence of moisture and oxygen promotes the oxidation of iron and aluminium, forming iron and aluminium oxides. These oxides are responsible for the characteristic reddish colour of laterite soils.
• Precipitation: As the soil solution becomes saturated with dissolved minerals, these minerals precipitate out, forming a hard, often cemented, surface layer. This contributes to the soil's characteristic hardpan.

Parent Material: Laterite soils typically develop from volcanic or sedimentary rocks rich in basalt, sandstone, or shale. The presence of these materials provides the necessary minerals for weathering and the formation of iron and aluminium oxides. The climate must be consistently warm and humid to facilitate the chemical weathering processes.

Characteristics of Laterite Soils:

• Reddish colour due to iron and aluminium oxides.
• Hardpan layer, making cultivation difficult.
• Low fertility due to leaching of essential plant nutrients.
• Poor water retention.