The Nature and Sustainability of Brazilian Amazon Soils

Around 45 per cent of the world’s humid tropical forests and savannas are found in South America and three-quarters of these are situated in the Amazon Basin. Taking the definition of the humid tropics to be those regions where there is less than a 5 degrees C variation in the mean monthly average temperature between the three coldest and the three warmest months, and with four months where potential evapotranspiration is greater than precipitation, the total world area is in the order of 1,500 million hectares with about a third or 500 million hectares in the Amazon (Nicholaides et al., 1984). According to a recent agronomic point of view, at least half of this area is considered to be potentially arable land or suitable for grazing (Sanchez et al., 1982a). A radically different point of view has been presented by a number of ecologists, such as Sioli (1980), Goodland and Irwin (1975) and Goodland (1980), who do not see either sufficient evidence that an agricultural technology has been developed to overcome the severe constraints of the environment, or that there is sufficient justification for removing one of the world’s most diverse ecosystems and replacing it by near-monocultural forms of land-use. Whichever point of view or compromise prevails, it is readily apparent that a sound understanding of the environment is essential and that the nature and dynamic properties of the soils forms a crucial part.