João Carlos Ker

Análise de componentes principais de atributos físicos, químicos e mineralógicos de solos do bioma cerrado

Behavior differences between soils of the South-American and Velhas geomorphic surfaces of the Cerrado region, all of them under native vegetation cover, were evaluated by physical, chemical, and mineralogical characterizations, and principal component analyses. According to their sub-region and geomorphic surfaces, the soils were separated in three groups: 1. clayey to very clayey texture, low- and mesoferric; 2. medium to sandy texture, lowferric; 3. clayey to very clayey texture, ferric. Water retention in the surface horizons of the studied soils was positively correlated with the clay and organic carbon contents. Soils of Group 3 showed the greatest amount of exchangeable bases in the surface horizons, which is mainly a consequence of the greater recycling efficiency imposed by the local forest formation when compared to the Cerrado formation (verified in 31 of the 33 soil profiles of Groups 1 and 2). Soils of Group 3, formed from mafic rocks, were the most homogeneous in mineralogical terms, since all profiles were hematitic. In averages, Groups 1 and 2 presented an overlapping mineralogical composition, though Group 1 is more gibbsitic than Group 2. In comparison to the US Soil Taxonomy, the efficacy of the Brazilian Soil Classification System at discriminating the studied soils is higher owing to the use of the ferric character in conjunction with the other attributes both systems have in common. The principal component analysis supported the understanding of the pedologic environment differences and similarities identified in the field.

Pedogenesis on the uplands of the Diamantina Plateau, Minas Gerais, Brazil: a chemical and micropedological study

Abstract Little is known about the soil distribution on quartzitic uplands of Brazil. The Diamantina Plateau, where deeply weathered oxisols (latosols) and shallow sandy soils occur side by side, represents part of the higher and oldest planation on the quartzitic uplands of Minas Gerais State. We studied representative soils from the Diamantina Plateau to help understand the pedogenesis and landscape evolution of this part of Minas Gerais. We found evidence of a lithological and tectonic control on the distribution of soils in the landscape. Polygenetic oxisols (Acrustox) occur at the top of the landscape at altitudes of 1300 m or more, resting uncomformably on quartzitic saprocks (Xanthic types) or mafic rocks (Rhodic types). They change downslope to in situ Quartzpsamments and Haplorthods. In the B horizon of the Xanthic Acrustox, quartz grains smaller than 0.3 mm are surrounded by gibbsitic plasma, forming subspherical microaggregates. Microaggregates in the Bw horizon of all upland oxisols display inherited features of intense biological activity regardless of the parent material or texture. The nutrient-poor catena of Xanthic Acrustox–Ustic Quartzpsamments–Oxyaquic Haplorthods represents a sequence of increasing hydromorphic conditions downwards, in which clay minerals are destroyed in low pH and ferrolysis. In the poorly drained soils downslope, low pH and eH induce the movement of reduced Fe 2+ and organic matter (OM)-bound Al and Fe both per descendum and through lateral flow downslope. In the bottom, micromorphological features and the chemistry of organic matter indicated that some Bsh horizons represent buried A horizons subjected to post-burial podzolization, corroborating morphological field data. This indicates the pertinence of the study of humic fractions in defining the Bhs (spodic) horizons of Brazilian spodosols.

Atributos físicos, químicos e mineralógicos de solos da região das Várzeas de Sousa (PB)

Physical, chemical and mineralogical characteristics of soils from the meadows of Sousa (Paraiba State - Brazil) were studied, as well as the effect of alkaline and alkaline-earthy cations on humic substance stability. Furthermore, criteria of environmental distinction used by the small farmers and different forms of land use in the studied region were identified. Profiles from the classes Ustifluvents (Neossolo Fluvico), Haplustalfs (Luvissolo), Natrustalfs (Planossolo natrico), and Usterts (Vertissolo cromico) were therefore selected, sampled and analyzed. Besides sodium, magnesium also had an effective participation in clay dispersion, mainly in the Usterts. Fe2O3 contents were low in all profiles, with a probable prevalence of less crystalline forms. The calcium-sodic mineralogy of the silt fraction is in agreement with the relative high content of calcium, magnesium and sodium. The outstanding presence of vermiculite/smectite and ilite was observed in the soil clay fraction of all soils. The high iron content in the clay fraction of Usterts suggests, besides the presence of hematite, the occurrence of 2:1 expansible mineral, rich in iron, possibly nontronita. The pre-treatment for carbonate elimination (HCl 0.1xa0molxa0L-1), applied during the humic substance fractionation, caused increases of 300 and 340xa0% for the humic and fulvic acid fractions, respectively, and a reduction of 60xa0% in the humin fraction, suggesting a participation of calcium and of magnesium humates and fulvates in organic matter stabilization.

Caracterização física, química, mineralógica e micromorfológica de horizontes coesos e fragipãs de solos vermelhos e amarelos do ambiente Tabuleiros Costeiros

The objective of this study was to evaluate the physical, chemical, mineralogical and micromorphological characteristics of cohesive red, yellow and grayish soils in a toposequence of the Coastal Tablelands region in southern Bahia and northern Espirito Santo states. It was also sought to understand the mechanisms promoting their cohesion and fragipan formation. Therefore, the routine physical analyses, determination of the coarse clay/fine clay ratio, specific surface by BET-N2 and water vapor adsorption, magnetic susceptibility, scanning-electron microscopy analyses and the micromorphology of thin plates were carried out. Physical and micromorphological analyses indicated that the high content of very fine clays, especially those smaller than 0.2xa0µm, translocated among horizons or within a same horizon as dispersed clay, were responsible for the genesis of the cohesive horizons. The higher cohesion observed in the Yellow Argisol (Ultisol) found in a drier climate, compared to those in a more humid climate could be due to the less clayey granulometry and a larger amount of clay illuviation features.

Dispersão de Latossolos em resposta à utilização de pré-tratamentos na análise textural

The accuracy of particle size analyses depends on a complete dispersion of the soil sample and the maintenance of the stability of the dispersed phase. In some Latosols the dispersion is hindered by microaggregates of high stability. These clay particles are partially detached by chemical and mechanical dispersion and because of their size, account for a systematic overestimation of the silt fraction in the analyzed soil. In order to minimize the amount of pseudo-silt in particle-size analyses of Latosols, an experiment was carried out to test how the efficacy of dispersion was affected by the use of pre-treatments for the removal of cementing agents. The treatments were set up in a factorial arrangement of 7 x 22. Study material were samples of seven Latosols dispersed with NaOH 0.01 mol L-1, with or without pre-treatment for the removal of organic matter and poorly-crystalline Fe and Al oxides. The silt fraction was dispersed again, and clay and silt proportions were determined after the second dispersion. The removal of organic matter and poorly-crystallized Fe and Al oxides increased the clay fraction yield, indicating the breaking up of microaggregates in sizes that correspond to other particle size fractions, especially silt. Pseudo-silt was found in all studied Latosols, in greater amounts in the more oxidic types. Coarse and fine sand fractions also presented clayey microaggregates that are not easily dispersed. After the second dispersion, the silt fraction presented values from 0.199 to 0.537 kg kg-1 of clay. Pre-treatments are recommended to reduce the proportion of pseudo-silt, especially the one used to remove poorly-crystalline Fe and Al oxides.

Caracterização de solos de duas toposseqüências em tabuleiros costeiros do sul da Bahia

The objective of the present study was to make the physical and chemical characterization of soils developed on sediments of the Barreiras group, in southern Bahia, as well as soils formed from rocks of the crystalline basement, which were taken as reference. For this purpose, soil horizon samples from two representative toposequences of the Coastal Plain were selected and analyzed: (1) eutrophic argisolic Red Latosol, latosolic dystrophic Yellow Argisol, duric orthic Ferrocarbic Spodosol; (2) dystrophic abruptic Yellow Argisol, dystrophic typic Yellow Argisol and duric orthic carbic Spodosol. Physical characteristics determined were texture, water dispersed clay, flocculation degree, and bulk density. The chemical analysis carried out were the following: pH in H2O and in KCl, Mg2+, K+, Na+, Al3+, H+ + Al3+, P, organic C and sulfuric acid attack. The soils of the two different topographic sequences differed regarding morphological and physical (texture) characteristics, mainly in the manifestation of the cohesive character. The Argisols inserted where the plateau was wider and less dissected presented a higher textural gradient and more pronounced cohesion state. The bulk density values for the cohesive horizons as well as for the fragipan and duripan were high and were inversely related with the organic matter content. The main micromorphological characteristics observed in the dense horizons of the Yellow Argisols were: low porosity and biological activity, and presence of illuviation argilans, confirming the presence of a textural B horizon.

Mineralogia, morfologia e análise microscópica de solos do bioma cerrado

As caracteristicas macro e micromorfologicas dos horizontes diagnosticos superficiais e subsuperficiais de Latossolos e Neossolos Quartzarenicos das superficies Sul-Americana e Velhas foram estudadas em perfis sob cobertura de vegetacao nativa, visando estabelecer um referencial para futuras comparacoes com areas similares sob constante intervencao antropica em termos de sustentabilidade. Com os solos referenciados por sub-regiao e pela superficie geomorfica que representam, tres agrupamentos foram constituidos: Grupoxa01: solos de textura argilosa a muito argilosa e hipo a mesoferricos; Grupoxa02: solos de textura media a arenosa e hipoferricos, e Grupoxa03: solos de textura argilosa a muito argilosa e ferricos. O horizontexa0Bw dos Latossolos argilosos e muito argilosos estudados (Gruposxa01 e 3), com relacoes cauliniticas/(caulinita + gibbsita) variando de 0,27 a 0,77, apresentaram grande coincidencia de estrutura e microestrutura, respectivamente, forte muito pequena granular e de microagregados. Os solos do Grupoxa02, Latossolos de textura media e um Neossolo Quartzarenico, apresentaram o plasma preferencialmente como peliculas aderidas aos graos que dominam o fundo matricial. A presenca marcante de agregados na fracao areia, resistentes ao tratamento para dispersao da terra fina, se deu apenas nos Latossolos argilosos e muito argilosos do Grupoxa03 (com carater ferrico) e em parte do Grupoxa01 (naqueles mais gibbsiticos). No leste de Goias, o horizontexa0Bw dos perfis de G2, Latossolos Amarelos de mineralogia gibbsitica e isenta de hematita, apresentaram feicoes observadas em lâmina delgada de cor vermelha e agregados residuais da fracao areia com hematita detectada pela difracao de raios-X, aspectos que corroboram a hipotese de um pedoambiente mais umido dessa posicao na paisagem relativamente a posicao G1, com perfis de Latossolos Vermelhos.

ATRIBUTOS MICROMORFOLÓGICOS DE SOLOS DO PROJETO JAÍBA, NORTE DE MINAS GERAIS

Undisturbed samples of representative horizons of soils from Jaiba Project, northern Minas Gerais, Brazil, and compacted and non-compacted layers of soils under intensive use were collected and micromorphologically analyzed to obtain more information on their evolution degree and also to evaluate the soil alterations caused by agricultural use. Four soils derived from limestone (P1 to P4) and one originated from detritic sediments (P5) were studied, as well as layers with and without indication of compaction. The micromorphological study revelead that the soils have very distinct and variable characteristics as a function of their classes and parent materials. The Cambisol (Inceptisol) originated from limestone has as a remarkable characteristic the vertical flux of silica and clay, without, however, characterizing textural (similar to argillic) horizon and a higher development of blocky structure. The Cambisol derived from detritic sediments presents a lateral flow of clay, a remarkable presence of iron diffusion skins and a less developed tending to granular structure. The Dark-Red Podzolic soil (Alfisol) showed blocky structure and the presence of deposition skins, many of these features being incorporated by the s-matrix, possibly an indication of transition to Latosol (Oxisol). The Latosols present granular structure, but this is much less developed than the corresponding one observed for the gibbsitic Latosols already analyzed in the country, what may indicate a smaller degree of evolution of these soils. The faunal activity seems to be the main responsible agent for the development of the Podzolic and Latosols microstructures. As for compaction, the micromorphological studies revealed differences in the plasm organization and in the form of pores when compacted and non-compacted layers were compared. In general, the plasm of the compacted layers is denser and the pores are altered as a function of the physical effort imposed to the soils.

Mineralização e sorção de atrazina em latossolo roxo sob cultivo convencional e plantio direto

A atrazina, herbicida do grupo das s-triazinas, foi utilizada em experimentos de laboratorio para estudos de mineralizacao e sorcao em amostras de Latossolo Roxo sob cultivo convencional e plantio direto. Atrazina-14C marcada no anel de triazina foi adicionada as amostras de solos, sendo o 14CO2 produzido e os extratos de atrazina-14C do solo analisados por cintilacao liquida. Os resultados mostraram taxas de mineralizacao de atrazina muito baixas, apresentando correlacoes significativas com os teores de carbono, nitrogenio total e fracoes humicas do solo. A mineralizacao de atrazina decaiu em profundidade, e o Latossolo Roxo sob sistema plantio direto mostrou maior mineralizacao de atrazina em virtude dos maiores teores de carbono. Em contrapartida, a fase lag do plantio convencional foi mais curta, evidenciando maior adaptacao microbiana nos solos sob manejo convencional, onde o herbicida e mais intensamente utilizado em pre-emergencia. Com a adicao de substratos orgânicos, houve aumento no processo de mineralizacao de atrazina. Verificou-se que a atrazina contem um componente rapido de sorcao no Latossolo Roxo, em torno de duasxa0horas, e um componente mais lento que se estabelece ate 12xa0h. A materia orgânica do solo foi o principal fator responsavel pela sorcao da atrazina (50% da atrazina adicionada) ao longo do tempo, enquanto os oxidos de ferro/aluminio e minerais de argila 1:1 nao contribuiram, de forma significativa, para a sorcao (5% da atrazina adicionada). Solos com baixo teor de materia orgânica podem nao reter atrazina em quantidades suficientes para evitar a contaminacao subsuperficial, onde a molecula nao pode ser mineralizada, trazendo riscos de contaminacao do lencol freatico.

Gênese de horizonte coeso, fragipã e duripã em solos do tabuleiro costeiro do sul da Bahia

The genesis of cohesive horizons in some soils is not well known yet and, in many cases, it is conflicting. The purpose of this study was to evaluate physical, chemical and mineralogical mechanisms that cause hardening in soils with cohesive horizons, fragipan and duripan in Brazilian Coastal Plain soils. Soil samples of two toposequences were sampled and the taxonomic classes of the soils were identified as Argisolic Eutrophic Red Latosol, Latosolic Dystrophic Yellow Argisol for the first toposequence, and Abruptic Dystrophic Yellow Argisol, Dystrophic Typic Yellow Argisol and Duric Orthic Carbic Spodosol, for the second sequence. The chemical analysis performed were Fe, Si, and Al extraction with sodium dithionite-citrate-bicarbonate (DCB) and ammonium oxalate. The clay fraction mineralogy was evaluated by X-ray diffraction. Soils with cohesive horizons presented very low Fe, Si, and Al contents extracted with both DCB and oxalate. Nevertheless, soil with fragipan and duripan showed high Si and Al content extracted with oxalate, indicating their role as cementing agents. The Argisol clay fraction is predominantly kaolinitic, and gibbsite was only found in the Bt1, Bt2 and Bw horizons of the Latosolic Yellow Argisol. Gibbsite was found in soils with fragipan and duripan (Duric Orthic Carbic Spodosol), and despite being considered a disorganizing agent of kaolinite adjustment, the hardpan characteristics were maintained. Thus, the hardening mechanisms of these soils seem different for cohesive, fragipan and duripan horizons.