Soils of Cerrados, the Brazilian Savannas

Abstract

Cerrados are the savanna-like vegetation of central Brazil. The first accounts on Cerrado soilsCerrado soils date back to the 1950´s, but increasing knowledge about soil characteristics under this vegetation derived from the outstanding expansion of modern agriculture on mostly low fertility, acid and deep cerrado soilsCerrado soils. We report the current knowledge about soils under Cerrado vegetation within the Brazilian territory, emphasizing its genesis and classification considering the Brazilian System of Classification of Soils-SiBCS, and land use aspects. In central Brazil, the Cerrado Biome covers extensive areas of Goiás, Distrito Federal, Tocantins, Bahia, Maranhão, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Piauí, Rondônia and São Paulo states, and many disjunct, isolated areas across Brazil, occupying more than 2,000,000 km2. Geomorphologically, cerrados are mainly found on extensive highland plateaus, but also occur in gently dissected to hilly landforms. Most Cerrado soils are dystrophic (base saturation less than 50%), and the few eutrophic soils identified always present strong limitations to a normal plant development, either physical or chemical. With the exception of clayey Latossolos of high plateaus, practically all other soils, besides the low natural fertility, present some physical limitations to plant development, such as: presence of abundant gravels and/or concretions (petroplinthite, mainly); high water table; high stoniness or rockiness; low water holding capacity; sandy or medium light texture; shallow depths. The Latossolos with clayey texture of the Central Tablelands and Plateaus are the preferred soils for high tech grain production, and commonly have an acric character, with positive ΔpH, in addition to the low natural fertility. Other Latossolos under Cerrado are either (i) of medium texture and low water retention capacity, or (ii) are clayey with very low CEC. The high aluminum saturation (>50%), postulated by pioneer authors as a conditioning factor of the Cerrado vegetation is controversial, and has not been confirmed, since many soil surveys throughout Brazil revealed the occurrence of Cerrado vegetation on soils without high Al saturation (such as the acric types). It is consensual that Cerrado occurrence is more related to soil water availability than to soil fertility, even though Cerrado on waterlogged soils are also found. The Central Brazilian Plateau, representing the core area of Cerrado, is part of a very old and stable landmass, unaffected by marine invasions and glaciers, where widespread planation and erosion allowed a very extensive smooth surface to develop. Most vegetation in the Central Plateau has been subjected to Quaternary climate oscillations, from semiarid climates during glacial periods, to humid climates during interglacials. The common occurrence of Cerrado in the Central Plateau High Tablelands (Chapadas) is closely associated with deep Latossolos of clayey or very clayey texture. However, different types of Cerrado, from Grassy to Woodland (Cerradão), are found, and such variations cannot be explained solely by chemical or physical attributes, but rather by external, anthropogenic factors, such as burning intensity, cattle grazing and selective clearing for wood or charcoal production, besides topographical and hydrological attributes. Despite the general low fertility, high productivity and high yields of soya, sugarcane, eucalyptus, rice, wheat, cotton and maize are commonplace in the cerrados, highlighting the robust knowledge Brazil attained in converting low fertility soil into areas where two successive crops are now possible. However, conservation issues are now pressing, since Cerrado vegetation, a major biodiversity hotspot in the neotropics, is vanishing at alarming speed.