A review of soil and soil-related constraints to development in Amazonia

Abstract

The Amazon Basin is a major landscape feature in South America, comprising a substantial proportion of the land area of at least four (Brazil, Venezuela, Colombia and Peru) states. To these states and others with Amazonian territories, this land area is generally characterized by low population densities; for example the Brazilian Amazon comprises approximately 40 per cent of the land area of Brazil, but is occupied by less than 4 per cent of the country's population. Viewed in terms of production this land is considered by many to be wasted, and there are considerable political and economic pressures to develop the area. A major area of current and planned development is in the broad sphere of agricultural production, either by improving the productivity of established programmes or by expanding the area cleared for agriculture. However, to date few schemes have been successful. The most extensive soils in the Amazon Basin are oxisols, ultisols and, to a significantly lesser degree, alfisols. The major constraints to agricultural development are chiefly soil and soil related, which may include low cation exchange capacity, deficiencies of plant nutrients and aluminium toxicity. Once the natural ecosystem is disrupted for agricultural production, and where care is not taken in the clearance of the natural vegetation, there may be physical constraints on production as soil stuctural properties are disrupted. When intensive agricultural production is established on cleared lands it is difficult to sustain it beyond the first few years without substantial inputs of fertilizers. The future potential of this area may only be fully realized if agricultural activities take account of the efficient manner in which the natural ecosystem functions, paying particular attention to the cycling of organic matter and the maintenance of a vegetation cover. Trees, in some form of agroforestry system, may offer the only sustainable agricultural production system.