More than 20 distinct soil regions can be found on the South American continent as a result of its geologic history, topography, climate, and vegetation. Three major groupings correspond to the continent’s three primary land regions—the lowlands, the highlands, and the Andes.
Low natural fertility is a conspicuous feature of soils in the humid tropic regions of South America. About half of the continent’s soils consist either of unconsolidated and nutrient-poor sediments (e.g., kaolins [china clays] and quartz sands) deposited in river basins, latosols (red soils leached of silica and containing residual concentrations of iron and aluminum sesquioxides), red-yellow podzols (acidic soils with a bleached upper horizon, or layer, that are low in lime), and regosols (azonal soils consisting mainly of imperfectly consolidated material and having a complex morphology). About one-fifth of the continent is covered by arid soils of various types in which agriculture is risky without irrigation.
Other regions, representing about 10 percent of the total area, are poorly drained, the soils being either gleys (clayey soils in which the substrate is bluish gray, generally sticky, and often structureless because of excessive moisture), groundwater laterites, grumosols (soils with a high content of expanding clays), or planosols (a type of soil found in humid climates in which soluble salts and minerals are leached out of the upper layers and are cemented or compacted at a lower level). In the Andes, slopes are often steep, and lithosols (shallow soils consisting of imperfectly weathered rock fragments) abound, accounting for another 10 percent of the continent’s surface. In the inter-Andean valleys and on some of the foothills, nevertheless, eutrophic soils (deposited by lakes, and containing much nutrient matter, but often shallow and subject to seasonal oxygen deficiency) can be found.
Fertile soils, therefore, extend over only about 10 percent of the surface of South America. The most important of these are brunizems (deep, dark-coloured prairie soils, developed from wind-deposited loess), chestnut soils, and ferruginous tropical soils. On the low coastal ranges, in the foothills of the western Andes, and on the nearby plains and terraces of Colombia and Ecuador, the soils consist mainly of red-yellow latosols, podzols, and alluvial soils. Soils in southern Brazil and Uruguay consist of brunizems, reddish prairie soils, and planosols. The Argentine Pampas, the largest fertile area on the continent, is uniformly covered with the so-called pampean loess, which is calcareous, rich in minerals, and mixed with volcanic sediment.Less rich soils are found in the uplands of northeastern and central Brazil, consisting mainly of sandy regosols in the north and red latosols in the south. The agricultural development of South America closely reflects the distribution of soils according to their fertility. It is mostly confined to the eastern mid-latitude plains, in which is concentrated the production of cereal grains and cattle grazing; to the subtropical and temperate parts of the Andes, from Colombia to Chile, where grazing takes place and a variety of crops are cultivated; and to eastern and southeastern Brazil, where coffee, cacao, soybeans, and sugarcane are grown, while the interior plateaus are devoted to cattle grazing.
Soil erosion has ravaged a large part of the continent. |According to some estimates, in several countries half or more of the presently arable land has been severely damaged or ruined by poor land management. In the Andes, land that once produced high yields of wheat is now abandoned. Mountain forests are still cleared for cattle grazing and cultivation, which greatly accelerates erosion and ruins the soil of the region for years thereafter. Soil damage has been less severe in areas of relatively flat terrain. Campaigns for soil conservation or restoration have been implemented in most countries. "South America" © Emmanuel BUCHOT, Encarta, Wikipedia
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