Abstract--Many soils developed from volcanic rocks in southern Brazil exhibit spontaneous magnetization caused by the presence of fine-grained maghemite (3J-Fe203), but few attempts were made to quantify or characterize this important soil component. To that end, clays were separated from freely drained soils derived from acid (>~63% Sit2), intermediate (54-62% SiO~), and basic (--<53% Sit;) igneous rocks produced by the Paranfi flood volcanism. The sample set included soils with a wide range of pedogenic development on different landscape positions. The Fe oxide mineralogy of these samples was examined by using a combination of selective dissolution, magnetic susceptibility, and X-ray diffraction (XRD) techniques. Hematite and maghemite were the primary Fe oxides in mature soils (Oxisols, Ultisols, and Alfisols) developed from basic rocks; whereas goethite was dominant in all other soils, especially those formed from acid-intermediate rocks. The association of maghemite with basic rock materials suggests that it was primarily formed by oxidation of lithogenic magnetite. A strong, positive correlation (R 2 = 0.89) was obtained between mass specific magnetic susceptibility (X) of the clay fractions and maghemite contents estimated by XRD. Either method could be used for quantitative analyses, but X was more sensitive than XRD at low maghemite concentrations (<2 wt. %). The clay-sized maghemites were superparamagnetic with an estimated value for the mass specific magnetic susceptibility (X~f) value of 91,000 • 10 -8 m 3 kg ~ and frequency dependent variations of 10-15%. The maghemites also had low unit cell constants, which, if attributed entirely to replacement of Fe by AI, would correlate with AI substitutions in the range of 5-16 mole %. Selective dissolution of the soil maghemites was achieved by treatment of Fe oxide concentrates with 1.8 M I-I2SO 4 at 75~ for 2 h.

RESUMO: Os sistemas de preparo e manejo do solo determinam as condições físicas para o crescimento das plantas e produtividade das culturas. O objetivo deste estudo é o de avaliar algumas propriedades físicas de um Latossolo Vermelho distrófico, cultivado com mandioca, após dois anos de implantação em diferentes sistemas de preparo do solo. Os tratamentos utilizados foram: Plantio Direto (mobilização do solo somente ao longo das linhas de plantio); Preparo Mínimo (escarificação a 0,30 m, seguido de gradagem niveladora) e Preparo Convencional (aração, com arado de aiveca a uma profundidade de 0,25 m, seguido de gradagem niveladora). Avaliaram-se, nas camadas de 0-0,10 m e 0,10-0,20 m, as seguintes propriedades físicas do solo: densidade, volume de macroporos, microporos, a porosidade e a resistência do solo à penetração das raízes, a cada 0,05 m, até à profundidade de 0,40 m, em três diferentes épocas. Constataramse maiores valores de densidade do solo e menores valores de macroporosidade na camada de 0-0,10 m no plantio direto e preparo mínimo do solo. Resultados similares foram obtidos na avaliação da resistência do solo à penetração, independente da época de avaliação e da umidade do solo. Os sistemas de preparo mínimo e preparo convencional do solo proporcionam condições físicas menos restritivas ao crescimento das plantas, quando comparado com o plantio direto. Avaliações de médio-longo prazo são necessárias face às mudanças dinâmicas na qualidade física do solo, impostas pelos sistemas de preparo e manejo do solo e da cultura. Palavras-chave: propriedades físicas do solo, estrutura, plantio direto, escarificação, compactação SOIL BULK DENSITY, POROSITY AND RESISTANCE TO ROOT PENETRATION IN AN OXISOL MANAGED BY DIFFERENT SOIL TILLAGE SYSTEMSABSTRACT: Soil tillage and management affect soil physical conditions for plant growth and crop productivity. The objective of this research was to evaluate some soil physical properties of an Typic Haplorthox located in the Northwest region of the State of Paraná, Brazil, after two years of different tillage systems, with same crop. The tillage systems used were: No-tillage (cultivated only along the crop row -NT), Minimum Tillage (subsoiling to the 0.30 m depth, followed by leveling -MT) and Conventional Tillage (plowing with moldboard plow to the 0.25 m depth, followed by leveling -CT). The following soil physical properties were evaluated at the depths of 0-0.10 m and 0.10-0.20 m: soil bulk density (Bd), soil porosity, and the soil resistance to root penetration (SRP), which was evaluated at each 0.05 m up to 0.4m, during three different periods. The results suggest showed higher values of Bd and smaller values of macroporosity in the 0-0,10 m layer for NT and MT. Similar results were obtained for SRP, independently of the time of evaluation and soil water content. MT and CT may provide favorable soil physical conditions to the growth of the crop when compared to NT. Medium to long-term evaluations are necessary due to the dynamic changes in soil physical quality, res...

Recebido em 19/5/00; aceito em 4/10/00 APPLICABILITY OF ADSORPTION MODELS TO THE STUDY OF COPPER BEHAVIOUR IN CLAYEY SOILS. It was evaluated the applicability of Langmuir, Freundlich and Temkin models to copper adsorption in three classes of soils. Fractions of each soil were added to test tubes containing growing concentrations of the metal in solution. The tubes were shaken and the copper concentrations were determined in the extracts by atomic absorption spectrometry (AAS). The models offered a good fit for the experimental data indicating that presence of silicated clay had high influence on copper sorption. The Langmuir isotherm showed high influence of the organic matter in the absorption phenomenon. It was evidenced the importance of further studies related to Temkin model. Keywords: adsorption isotherms; heavy metal; tropical soils. Quim. Nova, Vol. 24, No. 3, 324-330, 2001. Artigo INTRODUÇÃOVarios estudos ambientais indicam que o homem tornou-se o mais importante fator no ciclo biogeoquímico de metais pesados. A mobilização destes poluentes para a biosfera tem alcançado níveis preocupantes 1 . O solo é um componente muito específico da biosfera, pois além de ser um depósito geoquímico de metais contaminantes, controla também o transporte destas substâncias para a atmosfera, a hidrosfera e a biota. A presença destes contaminantes no ambiente possibilita a bioacumulação e a biomagnificação na cadeia alimentar, proporcionando distúrbi-os nos processos metabólicos dos seres vivos. A bioacumulação e a biomagnificação encarregam-se de transformar concentrações normais em concentrações tóxicas para diferentes espécies da biota e para o próprio homem 2 . Deste modo, a poluição do solo por metais pesados tem sido reconhecida como um importante problema ambiental, podendo ocasionar riscos ainda desconhecidos para a saúde de gerações futuras 3 . O cobre, além de ser um metal pesado 4 , atende aos critérios de essencialidade para plantas e microrganismos, sendo classificado como micronutriente. A literatura 5 descreve a concentração média deste metal no solo como de 20 µg.g -1 com variações na faixa de 6 a 80 µg.g -1 , porém, pode ser acrescido ao meio por resíduos urbanos e industriais, pesticidas e fertilizantes, entre outros 2 . Em grandes concentrações, pode proporcionar efeitos tóxicos ao tecido vegetal e causar a deficiência de outros nutrientes essenciais através de interações antagônicas 6 . A dinâmica do cobre no solo é bastante complexa e altamente afetada por inúmeros fatores do meio, principalmente a composição química, física e mineralógica do solo, a quantidade de matéria orgânica e o pH 7 . Para uma melhor compreensão dos fatores que controlam o comportamento deste metal no solo, faz-se presente um breve comentário a respeito das características químicas e mineralógicas do meio em questão.O solo pode ser definido como uma mistura de materiais inorgânicos e orgânicos, formados a partir de uma série de processos operantes na superfície terrestre que ocasionam a decomposição de rochas e minerais primári...

In the present paper, the adsorption of amino acids (Ala, Met, Gln, Cys, Asp, Lys, His) on clays (bentonite, kaolinite) was studied at different pH (3.00, 6.00, 8.00). The amino acids were dissolved in seawater, which contains the major elements. There were two main findings in this study. First, amino acids with a charged R group (Asp, Lys, His) and Cys were adsorbed on clays more than Ala, Met and Gln (uncharged R groups). However, 74% of the amino acids in the proteins of modern organisms have uncharged R groups. These results raise some questions about the role of minerals in providing a prebiotic concentration mechanism for amino acids. Several mechanisms are also discussed that could produce peptide with a greater proportion of amino acids with uncharged R groups. Second, Cys could play an important role in prebiotic chemistry besides participating in the structure of peptides/proteins. The FT-IR spectra showed that the adsorption of amino acids on the clays occurs through the amine group. However, the Cys/clay interaction occurs through the sulfhydryl and amine groups. X-ray diffractometry showed that pH affects the bentonite interlayer, and at pH 3.00 the expansion of Cys/bentonite was greater than that of the samples of ethylene glycol/bentonite saturated with Mg. The Mössbauer spectrum for the sample with absorbed Cys showed a large increase ( approximately 20%) in ferrous ions. This means that Cys was able to partially reduce iron present in bentonite. This result is similar to that which occurs with aconitase where the ferric ions are reduced to Fe 2.5.

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