This study investigated the influence of soil factors on the structure, richness and distribution of woody Cerrado species within the National Forest of Paraopeba, Minas Gerais State, Brazil. Individuals with basal stem circumference $ 10 cm were sampled in five plots of 20 3 100 m. The study was conducted in five environments with different physiognomies and types of soils. A total of 132 species were recorded. The species with the greatest importance values varied between different areas, as did structure. Canonical correspondence analysis ordination showed three different groups closely related to soil fertility and Al levels. These relations were also confirmed by Pearson's correlation where richness was positively related to pH, K, Ca, Mg and P and negatively to Al. The basal area was positively correlated with levels of P, Mg, Ca and T (base saturation) and negatively with Al, also using Pearson's correlation. Likewise, density was positively correlated with Mg and negatively with Al. The analysis shows that soil fertility and the concentration of Al are two of the most important factors responsible for structural and floristic variation and for differentiating dystrophic and mesotrophic Cerradão.

The Indian black earth (IBE) anthrosols (Terra Preta) overlying deep weathered kaolinitic soils of Western Amazonia represent one of the most interesting features of the Amazon Basin, with broad implications to human ecology. We studied one IBE site, in particular the chemical composition and forms of phosphate and potassium, micropedological attributes, and their ecological implications. In the IBE anthrosol, high levels of available P were due to the presence of comminuted fish and animal bone apatite. Flakes of 2 : 1 layer silicates rich in K occurred in pottery remains in the IBE, indicating that they were manufactured from neighbouring 'Várzea' soils. Amazon 'Várzea' environs were the only source of the soil material for pottery, since K-rich 2 : 1 minerals are not present in Terra Firme kaolinitic sediments. High available and total P contents of IBE were related to abundant, very small particles (5–60 μm) of Ca-P and Al-P forms, resolved by s.e.m./EDS at very high magnification. These features originated in animal bones and fish spines that have chemically altered in the soil environment. Earthworm and other biological channels exhibited high Al/P contents, due to apatite ingestion, comminution, and alteration. In transitional horizons, abundant secondary Al/P was present in biological channels, indicating intense biological activity down to 1.5 m. In deeper B horizons, apatite fragments are rare. Charcoal residues of incompletely combusted wood are widespread down to the B horizon. No spatial or concentration relationships exist between P and total free-iron in the soil.

A typical altitudinal sequence of four soil profiles from one of the uppermost areas of the Mantiqueira Highlands (Minas Gerais State, southeastern Brazil) was studied regarding physical, chemical, mineralogical and micromorphological attributes. The soils were classified as a Terric Haplosaprist, a Humic Xanthic Hapludox, a Typic Haplorthod and a Humic Psammentic Dystrudept. All soils are gibbsitic, highly acidic and distrophic, with high aluminium saturation. The high organic carbon content and coarse texture favour the occurrence of podzolization. Intense hydrolysis and mineral dissolution occur in the studied pedoenvironments, with the presence of adsorbed Al polymers and organic matter bound Al forms. Podzolization can only be confirmed with the combined analysis of soil humic fractions, Al forms and micromorphological attributes. The conspicuous presence of gibbsite is attributed to past conditions of deep weathering and saprolite formation. Closed nutrient cycling is essential for environmental sustainability due to the very low nutrient reserve of soils and deep pre-weathered saprolites. The highland subtropical environment is an important site of natural carbon immobilization in the tropics in which histic/humic horizons are the most important loci of carbon inputs. D

RESUMOUm experimento foi realizado em casa de vegetação com o objetivo de examinar as modificações provocadas por ciclos de umedecimento e secagem em amostras de Latossolos com diferentes mineralogias, em agregados integrais ou quando destruídos por moagem. Amostras de terra fina seca ao ar foram passadas em peneira de 1,0 mm e subdivididas em grupos: solo integral não moído e solo moído em almofariz e passado em peneira de 0,105 mm. O solo moído foi ainda subdividido em solo moído puro ou adicionado de ácido húmico purificado. Os materiais foram montados em cilindro de alumínio e submetidos a dez ciclos sucessivos de umedecimento e secagem, realizados por ascensão capilar, seguidos por secagem ao ar, com intervalo de sete dias entre cada ciclo. Após o término dos ciclos, os solos foram impregnados com resina de poliéster, montando-se seções finas para microscopia, as quais foram levadas para observação em microscópio ótico e fotografadas. As imagens obtidas foram digitalizadas, analisadas e quantificadas por meio do programa QUANTIPORO, desenvolvido no Departamento de Solos/Universidade Federal de Viçosa. Os resultados mostraram completa modificação na forma e no padrão da estrutura após a aplicação dos ciclos nos tratamentos que sofreram destruição de agregados por moagem. Essas mudanças foram atribuídas a uma reacomodação dos agregados fragmentados com a retração do plasma, que se seguiu ao processo de secagem. Todos os materiais estudados mostraram uma estrutura bem diferente da estrutura primária original destes solos. Não se observou qualquer tendência à reversão da estrutura após os dez ciclos, demonstrando que outros fatores, além dos físico-químicos e mineralógicos, devem ser invocados para explicar a gênese de microagregados em Latossolos.

Despite the agricultural importance of Indian Black Earth (IBE) in the Amazon region, there are few studies that report on the relation between soil texture and chemical fertility of IBE. These soils of pre-Colombian origin, with high contents of P, Ca and other nutrients are found across the Amazon valley. IBE profiles were studied to evaluate the total contents of P, its primary chemical forms and the P transformation phases in areas with IBE soils of variable texture and in adjacent reference soils. The soil texture strongly influenced soil fertility, changing in terms of transformation of the primary P forms and, consequently, predominant P forms in IBE. Soils with texture varying between clay and heavy clay had higher total P contents and primary Ca-P forms. Highest P-Al and lowest total P amounts were observed at the site Rio Preto da Eva, where texture varies from sandy loam to sandy clay loam. In the IBE with clay texture the amounts of soluble P, extracted with NH4Cl were highest, although different from Mehlich 1-extractable amounts.