C. E. G. R. Schaefer

Características da porosidade de um Argissolo Vermelho-Amarelo submetido a diferentes sistemas de preparo de solo

The porosity characteristics of a Red-Yellow Podzolic was evaluated after 10 years of cultivation, under the following soil management treatments: no-tillage, moldboard plowing + disking, disk plowing + disking, off-set disk harrowing followed by moldboard plowing + disking, off-set disk harrowing followed by disk plowing + disking and off-set disk harrowing followed by disking. Undisturbed 15 cm high and 15 cm deep soil blocks, were sampled for morphometric analysis of the soil porosity. Results indicated the presence of surface sealing and discontinuity between top and subsurface in treatments where offset disk harrowing was employed. The no-tillage system showed higher connection between macropores, without discontinuities between the topsoil and deeper layers.

Mineralogia das frações areia, silte e argila de sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

To investigate the mineralogical variations with depth, 11samples were collected down to 14m, in an exposed sediment packet of the Barreiras Group in Aracruz, Espirito Santo, Brazil.The sand, silt and clay fractions were studied by X-ray diffraction, differential thermal analysis, thermogravimetry and electron microscopy.The total contents of Fe in the clay and silt fractions and Ti and Zr in the silt fraction were determined by ICP after fluoridric acid extraction.Clay and silt fractions were submitted to selective and sequential mineral extractions, to characterize and quantify their constituents.The sand fraction showed a uniform mineralogical composition, almost solely quartz, with small amounts of mica, anatase, kaolinite and iron aggregates.In the 2.1; 4.2 and 7.7m depths, the occurrence of iron mottles with dark-red colour was observed.Silt fraction, as well, is constituted mainly by quartz, with stable kaolinite aggregates and hematite.The clay fraction showed a high proportion of kaolinite, reaching 950gkg-1 at 14m depth.The low contents of Fe in the sediments and the humid conditions of the Coastal Tablelands favored kaolinite concentration and removal of minerals, mainly Fe oxides. Contents of Goethite (main Fe oxide in the sediment) decreased with depth.The amount of low cristalinity material in the clay fraction is small, varying from 3.2 to 24.0gkg-1 for ammonium oxalate extraction and from 0.6 to 3.5gkg-1 for extraction with 0.5molL-1 NaOH, due to the high degree of development of the sediments.For the same reason, the mica contents in the clay and silt fractions were lower than 5.0gkg-1.As observed for kaolinite, the mica content in the clay fraction increased with depth.

Propriedades químicas e cristalográficas da caulinita e dos óxidos de ferro em sedimentos do grupo barreiras no município de Aracruz, estado do Espírito Santo

Detailed chemical and crystal properties of the kaolinite (Ka) and iron oxides in the Barreiras Group soils and sediments (Coastal Tablelands) are little known. Eleven samples were collected (0,7; 1,4; 2,1; 2,8; 3,5; 4,2; 4,9; 5,6; 7,7; 10,5 and 14m) in an exposed sediment sequence in Aracruz, Espirio Santo State, Brazil, in order to study the characteristics of these minerals with depth. Clay and silt fractions were studied by X-ray diffraction (XRD), differential thermal analysis and electron microscopy. Total contents of Fe, Cr, Mn, Ni, Pb, Ti and Zr of the clay fraction were determined by ICP after fluoridric acid extraction. The contents of Al, Si and microelements were determined in ammonium oxalate (AO) and dithionite-citrate-bicarbonate (DCB) extracts. The chemical composition of kaolinite in the clay fraction was determined by extraction with NaOH 5molL-1 and in the silt fraction by the combined heating and extracting with NaOH 0,5molL-1. The average Fe2O3 content in the kaolinite of the clay fraction (20.7gkg-1) was higher than those obtained for the silt fraction (5.2gkg-1). The interplanar space, mainly in the b axis, was increased, due to Fe substitution in the kaolinite structure. The properties of kaolinite (such as size and shape) did not substantially differ with depth, although less crystalline kaolinite was found at the surface, suggesting an interference of organic matter. With reference to the iron oxides, the Fe2O3 contents extracted by DCB in the clay fraction decreased with depth. The isomorphic substitution of Fe for Al was greater in goethite (Gt) in relation to hematite, with a trend of higher values at the sediment surface. The iron oxides presented little association with microelements, mainly, Ni, Pb and Ti.

Potássio e magnésio em minerais das frações areia e silte de diferentes solos

Os solos mais intemperizados, desenvolvidos nos tropicos umidos, apresentam baixa reserva de nutrientes nas fracoes mais grosseiras. Para avaliar a presenca de potassio e magnesio nos minerais, amostras das fracoes areia e silte de solos desenvolvidos de diferentes materiais de origem e estadios de intemperismo dos estados de MG, ES, RS e RR foram estudadas por difratometria de raios-X (DRX), analise termodiferencial, analise termogravimetrica diferencial e microscopia eletronica. Os teores totais de elementos da TFSA e das fracoes do solo foram determinados por digestao fluoridrica das amostras. A fracao silte tambem foi submetida a extracoes sequenciais e seletivas dos minerais para estimar a contribuicao das especies minerais nos teores totais de K e Mg. A fracao areia dos solos mais intemperizados e muito pobre em nutrientes, com predominio de quartzo, indicando limitada reserva de K e Mg. Para os solos mais jovens, esta fracao apresenta os maiores teores totais de K e Mg, superando as fracoes mais finas do solo, com presenca de minerais primarios, como mica, feldspato e anfibolio. Particulas de mica e agregados de caulinita foram as principais fontes de K e Mg totais para as fracoes areia e silte dos solos mais intemperizados. Os minerais micaceos nestes solos, identificados e analisados por microscopia eletronica, apresentaram teores de K2O variando de 33,3 a 62,8 e 27,4 a 98,1 g kg-1 e de MgO de 76,5 a 116,8 e 19,7 a 68 g kg-1 para as fracoes areia e silte, respectivamente. Devido aos baixos teores de mica na fracao silte dos solos mais intemperizados (menor que 1%) e a alta proporcao de quartzo, mesmo apos a extracao de caulinita, a concentracao da amostra nao foi suficiente para deteccao de minerais micaceos por DRX. Apenas para o LV de Barroso (MG), verificou-se o aparecimento de discreta reflexao de mica.

Efeitos de ciclos de umedecimento e secagem na reorganização da estrutura microgranular de latossolos

A greenhouse experiment was conducted to examine the structural modifications engendered by wetting-drying cycles in Latosol samples (Oxisols) with different mineralogical properties submitted to dry grinding, compared with bulk samples. Air-dried soil samples were sieved through a 1.00 mm sieve and separated in two groups. One was kept as control group and the other ground in a mortar and sieved through a 0.105 mm sieve. This second was also split in two groups, one of which received particulate humic acid treatment. The materials were placed in aluminum columns, subjected to 10 weekly wetting cycles by capillarity followed by air-drying. At the end of the cycles, the samples were impregnated with polyester resin, cut in blocks and thin-sectioned for microscopy analysis. The sections were scrutinized under optical microscope, photographed, and the images digitalized, analyzed, and quantified with the Software QUANTIPORO. After the wetting and drying cycles, important alterations in both shape and structural pattern were observed in the ground samples. These changes were attributed to a re-organization of soil particles during the plasma shrinkage after the drying process. All materials presented a different structural pattern in relation to the original soil structure. No trend for reversion to the original structure was observed after the cycles. This indicates that other factors besides the physical-chemical and mineralogical should be considered to explain the genesis of Latosol microaggregates.

Occurrence of magnetite in the sand fraction of an Oxisol in the Brazilian savanna ecosystem, developed from a magnetite-free lithology

It is relatively well established from many pedogenetic studies that, in deeply weathered Oxisols from Central Brazil, magnetite or maghemite are either inherited or transformed from magnetite of the mafic parent material. However, no similar pedogenetic pathways have been reported in the literature for other lithologies, such as limestone and pelitic rocks (shales and slates) of the BambuGroup in Brazil. In these sedimentary, non- mafic lithologies, magnetic minerals are not likely to occur. Despite that, magnetic nodules were identified in a representative Oxisol pedon developed on this pedodomain, under savanna (Cerrado). Magnetic and non-magnetic fractions of nodules were separated with a hand magnet. Chemical and mineralogical compositions of these nodules were determined by conventional chemical methods, powder X-ray diffractometry (XRD), and 298 K M¨ ossbauer spectroscopy. For the magnetic fraction, containing up to 84 dag/kg of Fe2O3 but also relatively rich in Al, Ti, Cr, and Si, M¨ ossbauer measurements were also made at 4.2 K, without and with an externally applied magnetic field of 8 Tesla, and at 100 K. M¨ ossbauer results and structural Rietveld refinement of the XRD data consistently suggest that the iron oxide mineralogy corresponds to approximately equivalent proportions of hematite and a partially oxidised magnetite, containing 3 dag/kg of iron as FeO. Laboratory tests were conducted in an attempt to produce magnetic material by heating this non-magnetic fraction. The sample was wrapped in filter paper and heated at 300 ◦ C for 30 min, and the results were compared with the naturally occurring magnetic nodules. The saturation magnetisation value of the thermally treated sample was found to be σ = 7 J/T.kg, well below σ = 16 J/T.kg of the magnetic soil nodules. Mand XRD results indicate that the iron oxide mineralogy of this laboratory- produced magnetic sample also corresponds to a mixture of partially oxidised magnetite and hematite. Two other parts of the same non-magnetic, naturally hematite-rich precursor were mixed with charcoal, to act as reducing agent, and oven-heated at 450 ◦ C and 600 ◦ C, respectively, for 1 h, producing increasing reduction of the hematite to magnetite. These laboratory simulations support the model in which magnetite in these hematite-rich nodules was formed under the influence of seasonal burning regimes of the covering vegetation, followed by partial re-conversion of the magnetite particles to hematite under long-term atmospheric exposure to air. This model is consistent with a long-term, seasonal fire history, assumed for the genesis of the Cerrado ecosystem in the Central Brazil, although a wider validity for the entire BambuGroup area remains open. Additional keywords: M¨ ossbauer spectroscopy, Rietveld, iron oxides, BambuGroup.

Efeito da compactação do solo sobre a emergência de plântulas de soja em sistema plantio direto

Objetivou-se no presente trabalho, estudar os efeitos da combinacao entre teores de agua do solo e cargas aplicadas pela roda compactadora da semeadora-adubadora sobre a emergencia de plântulas de soja, em sistema plantio direto. A resistencia mecânica do solo a penetracao foi determinada quinze dias apos a semeadura. O indice de velocidade de emergencia foi determinado pela contagem das plântulas, sendo realizada diariamente ate que o numero de plântulas emergidas se apresentasse constante por tres dias consecutivos. O maior indice de velocidade de emergencia (IVE) ocorreu no teor de agua igual a 0,33 kg kg-1 e na carga de 86,21 N. A carga maxima de 140 N, aplicada pela roda compactadora sobre a semente, causou encrostamento superficial do solo, retardando a emergencia das plântulas.

Carbon Stocks in Brazilian Latosols (Oxisols) from Different Morphoclimatic Regions and Management Systems

Abstract Soil organic matter (SOM) is the greatest carbon reservoir in the terrestrial ecosystem, reaching approximately 1.500 × 109 t of carbon (C). The knowledge of the size and dynamics of this compartment is essential for carbon stock evaluation, leading to a national inventory of carbon fluxes, as well as the modeling of tropical carbon cycles. Latosols (oxisols) cover approximately 40% of the Brazilian territory, being important with regard to SOM accumulation. This process can occur both at the surface and within minute aggregates at greater depths. The mean C stock values were calculated for Brazilian Latosols (Red Latosol—RL, Yellow Latosol—YL, Red Yellow Latosol—RYL, and Humic Latosols—HL); in addition, we evaluated the effects of climate, vegetation, and land use on C stocks. A database was used of organic carbon contents of A and B horizon of Latosols from different morphoclimatic regions (humid tropical northern Brazil, semi-arid, northeast, coastal Atlantic southeast, dry topical central, and subtropical southern) compiled from the extensive RADAMBRASIL and EMBRAPA soil surveys. The mean C stock values of Brazilian Latosols are: 6 and 13 kg m−2 for YL; 7.5 and 11 kg m−2 for RL; 6.8 and 8.8 kg m−2 for RYL; and 30.16 and 15.78 kg m−2 for HL, for A and B horizons, respectively. Carbon stock values were markedly influenced by regional climate, type of vegetation, and land use. The usually neglected pool of organic carbon in B horizons of deeply weathered Latosols accounts for between 42–76% of the total C stocks.

Soil compaction around Eucalyptus grandis roots: a micromorphological study

This study aimed to evaluate the effects of Eucalyptus grandis root growth on localised soil compaction and fracturing. Undisturbed soil (Kandiustox) samples subjected to root growth pressure were used, employing 2 methods to study the phenomenon: (i) micromorphological analysis of thin sections of soil samples compacted by roots of 0.3, 0.9, 1.3, 2.8, 3.5, 6.4, 8.0, 9.0, and 10.2 cm diameter, carried out in the zone under direct root influence, up to 1 cm from the root–soil surface, compared with a reference area at a distance of 3 cm from the contact surface; (ii) a localised infiltration test to assess the time taken to infiltrate one drop of water into the surface of root-compacted soils, compared with the time taken in a reference sample without root compaction. The soil compaction was greater around root diameters >3.5 cm, and this effect was accompanied by reduced water infiltration in the soil surface at the root contact. Presence of chiseling fractures at an approximate 45° angle to the soil surface suggested helicoidal growth of the E. grandis root, causing both soil compression and shearing. At microscopic level the soil-root contact showed clay-oriented features, microfractures, fungi coatings, and micro-slickensides. The lower infiltration rate in the compacted soil–root surface is associated with both physical (compaction) and chemical (possibly hydrophobicity) mechanisms. The use of micromorphological techniques and image analysis allowed the observation and quantification of soil porosity in the vicinity of roots.

Preliminary evaluation of acid mine drainage in Minas Gerais State, Brazil

A despeito da importância economica de atividades mineralogicas para o estado de Minas Gerais, perceber-se que elas causam significativo impacto ao ambiente. Drenagem acida e um dos aspectos ambientais considerados pela atividade em funcao de seus impactos. Ela tem origem a partir da oxidacao de sulfetos metalicos que acidificam as aguas, com possibilidade de mobilizar elementos toxicos e poluir os recursos hidricos. Este trabalho teve como objetivo realizar uma avaliacao preliminar do problema em Minas Gerais. O trabalho teve inicio a partir de um levantamento bibliografico junto a Fundacao Estadual de Meio Ambiente (FEAM) para identificar mineracoes cujo minerio esta associado a sulfetos. Amostras dos substratos foram retiradas para determinar o potencial de acidez (AP) e de neutralizacao (NP). AP foi avaliado por dois procedimentos: pelo teor total de sulfetos e pela oxidacao com peroxido seguida da titulacao acida. O NP foi avaliado pelo teor equivalente de carbonato de calcio. Lâminas petrograficas foram preparadas para a descricao mineralogica com enfase em sulfetos e carbonatos. O balanco acido-base (ABA) foi determinado pela diferenca entre AP e NP, enquanto o potencial de geracao de aguas acidas foi obtido pelo valor de ABA e o volume total de material de cada atividade mineraria. Os resultados permitiram identificar quatro substratos com potencial para gerar drenagem acida no estado de Minas Gerais. Juntas, estes materiais representam um potencial de geracao de cerca 3,14 a 10,37 bilhoes de metros cubicos de agua a pH 2,0 ou 31,4 a 103,7 bilhoes de metros cubicos de agua a pH 3,0. Estes valores significam custos entre US