Pablo Vidal Torrado

Atributos de solos hidromórficos no Pantanal Norte Matogrossense

Resumo Os solos hidromorficos, comuns na Amazonia e no Pantanal, estao sujeitos a alternância natural de periodos de alagamento e secamento, que conduzem a uma formacao e caracteristicas diferenciadas. Estes solos guardam estreita relacao com a natureza do material de origem e com os processos de deposicao e sedimentacao. O objetivo neste trabalho foi avaliar as caracteristicas quimicas, morfologicas e mineralogicas de tres perfis de solos do Pantanal Norte Matogrossense (Planossolo, Plintossolo e Gleissolo), a fim de interpretar as relacoes entre suas propriedades e o ambiente em que foram formados. Os Planossolos e Gleissolos possuem maior fertilidade natural, evidenciada pelos valores expressivos de CTC (capacidade de troca de cations) e saturacao por bases. Os menores teores de Fe 2 O 3 do Planossolo estao relacionados com a reducao e remocao do Fe durante sua genese A mineralogia da fracao areia dos solos e constituida principalmente de quartzo, nodulos e concrecoes de Fe e de Mn, e em menor grau, biotita, muscovita e tracos de turmalina, magnetita, ilmenita, epidoto, zircao e rutilo. Os solos apresentaram perfil mineralogico semelhante na fracao argila, constituido por caulinita, esmectita, ilita e interestratificados do tipo ilitaesmectita. A mineralogia da fracao argila dos solos foi compativel com as diferencas quimicas constatadas entre eles, pois o Planossolo apresentou argila de maior atividade relativa as esmectitas e interestratificados ilita/esmectita, com maior soma de bases trocaveis e CTC, enquanto o Plintossolo e o Gleissolo, cujo mineral predominante foi a caulinita, apresentaram baixo teor de bases trocaveis e menor CTC. PalavRas-Chave: hidromorfismo, planicie de inundacao, ilita, argila de alta atividade. Attributes of the hydromorphic soils in the Pantanal of North Matogrosso

Composição lignocelulósica e isótopica da vegetação e da matéria orgânica do solo de uma turfeira tropical: II - substâncias húmicas e processos de humificação

Much of the organic matter of a typical peat consists of humic substances, mainly formed via humification of organic residues, decomposed by soil microorganisms, and by the polymerization of organic compounds to functional macromolecules, which are normally more resistant to degradation. The fundamental pathways governing the humification of soil organic matter (SOM) are not well understood so far, and most available data about the identified chemical precursors of humic substances and the main chemical routes by which they are transformed in the peat environment are still poorly understood. What is clear is that all routes involve lignin as a chemical intermediate. Stable isotopes (δ13C, δ15N) can be used to trace humification processes of the soil organic matter (SOM), by identifying their precursors. The purpose of this study was to compare the isotopic composition of vegetation materials from the two bog vegetation types that colonize a tropical highland peatland: moist grassland (CLU) and semideciduous forest (FES), based on the isotopic composition of humic substances of SOM. The whole area of the studied peatland occupies 81.75 ha. To identify the isotopic and lignocellulosic vegetation composition, materials of the dominant species of each vegetation type were sampled. Soil samples were collected from three representative sites per vegetation type, at intervals of 5 cm from the surface down to a depth of 50 cm. The humic substances were isolated from these samples; signals of δ13C and δ15N were determined for the humic fractions. The lignin and and δ13C values were higher in vegetation and SOM under FES than in SOM under CLU. Humin contents were high in SOM under both vegetation types; the levels of humic acids were higher in SOM under CLU than in FES; fulvic acid contents were higher in SOM under FES than CLU. The 13C values for lignin were highly similar to those for humic acids and fulvic acids. Variations in the lignocellulosic composition of the species that colonize the CLU and FES promote different rates and SOM humification products.

Relações entre matéria orgânica do solo e declividade de vertentes em toposseqüência de Latossolos do Sul de Minas Gerais

The accumulation and stability of soil organic matter are related to slope steepness. The relationships between steepness and the humification degree of humic acids, the charcoal fragment content and its radiocarbon age were quantitatively evaluated. Four Latosols (Oxisols) of the summit, shoulder, back slope and back/foot slope of a toposequence under pasture in a cratonic area in the southern Minas Gerais state, southwest Brazil, were used. The parent material of the Latosols was gneiss of the Precambrian complex, with an udic hydric regime and isothermic thermic regime. Samples were collected from every horizon and subhorizon of the four Latosols for chemical and physical characterization, humic acid extraction and determination of the semiquinone free radical content. Likewise, charcoal fragments were collected for gravimetric, nitrogen and carbon content quantification and radiocarbon dating. Our results show the close relationship of the accumulation and humification degree of soil organic matter in Latosol landscapes to slope steepness, whereas the quantity and radiocarbon age of charcoal fragments were related to the processes of soil genesis and soil position in the slope.

Geoquímica de solos do pantanal norte, Mato Grosso

Characterization and geochemical analysis of soils allows us to understand the processes of migration, dispersal, and concentration of chemical elements in the profile, serving as a basis for correlation of soil properties with the soil classes formed, which allows inferences about soil genesis. The aim of this study was to characterize and interpret the total geochemical composition of major and minor elements in soil classes representative of the northern Pantanal in the Barao de Melgaco subregion, Mato Grosso (Brazil). We selected 20 profiles of the major soil types of the Pantanal and analyzed samples of the A and B (or C) horizons in regard to the concentration of total oxides by X-ray fluorescence spectrometry, as well as physical, chemical, and mineralogical characterization. The soils are subdivided into two geochemical types: one composed of sandy to sandy loam soils with relatively high levels of SiO2 and predominance of kaolinite and quartz, with lower levels of trace elements and bases; and another composed of a more clayey soil texture, geochemically heterogeneous, with significant contents of 2:1 clay minerals, Al2O3, Fe and Mn oxides, alkalis, and trace elements.

Soil profile, relief features and their relation to structure and distribution of Brazilian Atlantic rain forest trees

In tropical forests, the environmental heterogeneity can provide niche partitioning at local scales and determine the diversity and plant species distribution. Thus, this study aimed to investigate the variations of tree species structure and distribution in response to relief and soil profile features in a portion of the largest remnant of Brazilian Atlantic rain forest. All trees ³ 5 cm diameter at breast height were recorded in two 0.99 ha plots. Topographic survey and a soil characterization were accomplished in both plots. Topsoil samples (0-20 cm) were taken from 88 quadrats and analyzed for chemical and particle size properties. Differences for both diversity and tree density were identified among three kinds of soils. A canonical correspondence analysis (CCA) indicated that the specific abundance varied among the three kinds of soils mapped: a shallow Udept - Orthent / Aquent gradient, probably due to differences in soil drainage. Nutrient content was less likely to affect tree species composition and distribution than relief, pH, Al3+, and soil texture. Some species were randomly distributed and did not show restriction to relief and soil properties. However, preferences in niche occupation detected in this study, derived from the catenary environments found, rise up as an important explanation for the high tree species diversity in tropical forests.

Rehabilitation with forage grasses of an area degraded by urban solid waste deposits

Dry matter yield and chemical composition of forage grasses harvested from an area degraded by urban solid waste deposits were evaluated. A split-plot scheme in a randomized block design with four replicates was used, with five grasses in the plots and three harvests in the subplots. The mineral content and extraction and heavy metal concentration were evaluated in the second cut, using a randomized block design with five grasses and four replicates. The grasses were Brachiaria decumbens cv. Basilisk, Brachiaria ruziziensis, Brachiaria brizantha cv. Marandu and cv. Xaraes, and Panicum maximum cv. Tanzânia, cut at 42 days of regrowth. The dry matter yield per cut reached 1,480 kg ha-1; the minimum crude protein content was 9.5% and the average neutral detergent fiber content was 62.3%. The dry matter yield of grasses was satisfactory, and may be an alternative for rehabilitating areas degraded by solid waste deposits. The concentration of heavy metals in the plants was below toxicity levels; the chemical composition was appropriate, except for phosphorus. The rehabilitated areas may therefore be used for grazing.