Geography – Soils in rainforests and savannas | e-Consult

Oxisols (found in tropical regions) and Latosols (similar soils found in tropical and subtropical regions) are formed in areas with high rainfall and alternating wet and dry seasons. The key weathering process is intense chemical weathering, particularly hydrolysis. This is driven by high temperatures and humidity, leading to the breakdown of parent material (often basaltic lava flows) and the leaching of soluble minerals like calcium, magnesium, and silica. This leaching process leaves behind insoluble iron and aluminium oxides, which give these soils their characteristic reddish-brown colour.

The alternating wet and dry seasons are crucial. During the wet season, intense rainfall promotes chemical weathering and leaching. During the dry season, evaporation concentrates salts in the soil profile. This process, known as 'pedoturbation', causes the soil to crack and crumble, further enhancing aeration and drainage. The lack of significant organic matter input due to the rapid decomposition in warm, wet conditions also contributes to the low organic matter content of these soils.

Oxisols/Latosols are primarily found in tropical regions near the equator, such as parts of Africa (e.g., Congo Basin), South America (e.g., Amazon Basin), and Australia (e.g., Queensland). Their development is strongly influenced by latitude and proximity to the equator, where high temperatures and rainfall are consistent. The geological history of the area, particularly the presence of basaltic lava flows, also plays a role in their formation. The soils are generally very acidic and have poor nutrient availability, making agriculture challenging without significant input of fertilizers.