Despite evidence to the contrary, the belief persists that the soils of the humid tropics are incapable of supporting sustainable agriculture and forestry. This belief is based on three main misconceptions about tropical soils: laterite formation, low soil organic matter content, and the role of nutrient recycling in agricultural systems.

LATERITE FORMATION

It has often been claimed that most soils of the humid tropics, when cleared of forest cover, will degrade irreversibly, ultimately forming brick-like layers known as laterite. Advances in the classification and mapping of soils show that areas in which laterite formation is a real threat are very limited and predictable (Sanchez and Buol, 1975). Only 6 percent of the Amazon region, for example, has soft plinthite in the subsoil, the substance capable of hardening into laterite if exposed by erosion. These soils occur in flat, poorly drained lands, where the danger of erosion is minimal. However, arid and semiarid regions of West Africa contain large areas of lateritic soils, especially in the West African Sahel.

Hardened laterite of geologic origin occurs in scattered areas in the humid tropics, where it serves as excellent road-building material. Low-cost roads in the Peruvian Amazon, which is essentially devoid of laterite formations, are inferior to those of the Brazilian state of Pará, where laterite outcrops occur. The laterite formation hazard, still frequently mentioned in the literature, is therefore of minimal importance