Data/hora: 06/06/2024 02:11:11

Biblioteca(s): 	Embrapa Cerrados; Embrapa Solos.	
Data corrente: 	06/11/2001	
Data da última atualização: 	06/11/2001	
Autoria: 	RESENDE, M.	
Título: 	Mineralogy, chemistry, morphology and geomorphology of some soils of the Central Plateau of Brazil	
Ano de publicação: 	1976	
Fonte/Imprenta: 	S.l.: Purdue University, 1976.	
Páginas: 	237p.	
Idioma: 	Inglês	
Notas: 	PhD Thesis.	
Conteúdo: 	Soil sequences from the Central Plateau of Brazil (Western Minas Gerais) developed from basaltic, sandstone, and clayey sediments were sampled. Oxisols from other parts of the country were used to test wider applicability of relationships studied. Particular attention was given to the relationship of landforms to vegetatation and soils. ERTS imagery was used to map broad soil landscape units. The soil samples and some rocks in different stages of weathering were examined in the laboratory for further studies. X-ray, DTA, IR, sequential extraction by dithionite-citrate-bicarbonate, magnetic susceptib lity and optical methods were used. Step-like land-surface characterize the study area. Highly permeable soils and lateritic (ironstone) gravel on the edges of the broad, very smooth surfaces (chapadas) protect these old surfaces against further erosion. It is suggested that the cerrado, a basically species-rich, low soil fertility adapted plant formation evolved, in this area, in the chemically very poor phyllitic-quartzitic rocks or preweathered sediments. Humid-dry climatic cycles, phased to interglacial-glacial periods, determined expansion-contraction of cerrado. During the contraction, in a humid climate, cerrado formed outliers in the chemically poor sites. Gibbsite-kaolinite ratio tends to be higher for cerrado soils than forest soils, and the ratios increase with iron content. Low organic matter regime (biomass production per unit time), more effective precipitation, or older surfaces are possible explanations of the higher ratios. Basaltic rock tends to form gibbsite. Lower silica content in the rock and adsorption of it by poorly crystalline iron oxides affect this phenomenon. Goethite with a high content of A1OOH, up to 30 molar percent, is mainly responsible for yellower colors of Oxisols (Latosols). The almost universal presence of goethite, even if in minute amounts in Oxisols, indicates high stability. Only 1% of finely powdered hematite changes Munsell hues of a clayey soil from 10YR to 5YR. The almost monomineralic iron oxide phase of yellower Oxisols justifies their separation. Goethite tends to be related to kaolinite reflecting basically a greater organic carbon regime. A reduced organic carbon regime in a still relatively humid climate affects the gibbsite-kaolinite system before changing the goethite-hematite system. In this case both gibbsite and goethite can be high. Magnetic susceptibility after heating samples up to 900o graus C shows na abrupt increase at 500o graus C. The increase is related to organic matter content. A reduction-oxidation mechanism seems to be operating but maghemite was not positively identified in the cooled material. The lack of positive evidence by x-ray and DTA for the presence of maghemite in the clay fraction of hematite-rich soil seems to indicate that the very small size and relatively high isomorphus substitution of hematite could be responsible for the high magnetic susceptibility of these soils	
Palavras-Chave: 	Brasil; Morfologia; Morphology.	
Thesagro: 	Mineralogia; Solo.	
Thesaurus Nal: 	Brazil; mineralogy; soil.	
Categoria do assunto: 	--	
Registro original: 	Embrapa Cerrados (CPAC)	
Exemplares: 	CNPS - (4475-1) - ADD - TS - -- - 76030 - RES/76 - 1997.01873 - DIS
CPAC - (20260-1) - ADD - TS - -- - CRI5583 -  - CRI5583 - DIS