Soils of the tropics and the world food crisis.

The properties and potential of soils of the tropics are poorly understood. The old idea that laterite is formed when tropical soils are cleared is true of only a small proportion of the area. In most features, soils in the tropics are similar or equivalent to soils in the temperate regions. Specifically, soil organic matter contents, commonly believed to be low in the tropics, are essentially similar to those of the temperate regions. While the basic concepts about physical and chemical behavior developed in the nonglaciated temperate regions are directly applicable to the tropics, the development of soil management practices for sustained food production involves different strategies because of environmental and economic constraints. A major distinction is made between the development of high base status and low base status soils. With the former, soil management practices should be aimed at maximizing the potential of high-yielding varieties and improving intercropping systems with relatively intensive fertilizer inputs. With the low base status soils of the vast savanna and jungle areas energyrelated inputs should be optimized by (i) selecting of crop varieties and species more tolerant to nutritional deficiencies or toxicities, (ii) applying fertilizers at lower rates than those recommended by classic marginal analysis, and (iii) increasing the efficiency of applied fertilizers in such soils.