ABSTRACT Soil evolves in landscapes in a natural process in which soil properties are gradually transformed. However, the transformation of argic to ferralic horizons in basic rock-derived soils under tropical conditions is poorly understood. Depending on the position of the soil profiles in landscape, evidence of pedogenetic transformation between different horizons might indicate the formation and destruction of aggregates with shiny faces. This study aimed to determine pedogenetic changes in basic rock-derived profiles in a toposequence, because soils derived from mafic rocks are not abundant in the study region (Pinheiral, Rio de Janeiro State, Brazil). Trenches were dug at the summit (P1), upper (P2), middle (P3), and lower (P4) thirds along the toposequence. The morphological, physical, chemical, mineralogical, and micromorphological properties of the profiles were characterized, and a weathering index was calculated from X-ray fluorescence element values. All profiles had chemical and physical properties indicating an advanced degree of weathering resulting from the parent material and tropical climate conditions. In P1 and P4 that were classified as Nitossolos, the most evident pedogenetic processes were ferralitization and nitidization, due to the advanced degree of weathering, accumulation of oxyhydroxides and kaolinite in the horizons, and formation of textural pedofeatures by mechanical-hydric stress and evidence of the illuviation process. Profiles P2 and P3 revealed a ferralitization process and were classified as Latossolos. Absence of shiny macromorphological ped faces in some Bw horizons, and their micromorphological coexistence in Bt and Bw horizons within the same profile were associated with the transformation of the blocky into a granular microstructure, suggesting argic-ferralic horizon transformation.

ABSTRACT Plinthite and petroplinthite occur frequently in Brazilian soils, but there is little information on the behavior of these materials. The aim of the present study was to assess the effect of different drying periods on the hardening and stability of plinthic materials of soils in the floodplain of the Araguaia River and the João Leite stream in Goiás. Soil samples were collected, with the aid of 0.10 m high and 0.15 m diameter PVC cylinders, directly from the plinthic horizons of five profiles of Plintossolos Argilúvicos (Plinthosols). Plinthite and soil matrix subsamples were obtained from these samples. Homogeneous petroplinthite samples were collected from the concretionary horizon of a Plintossolo Pétrico (Plinthosol) profile, and these were separated into subsamples with the aid of a rock hammer. All subsamples were dried in two manners: air drying and drying in a forced ventilation oven for 10, 20, 40, 80, and 160 days. Compressive strength and degree of stability were assessed. The results show a considerable variety of responses to the compressive force applied to the plinthite and petroplinthite samples in the same horizon and among the different profiles examined.

ABSTRACT: Records of changes in the phytosociological structure of vegetation can be observed more clearly in soils that have more significant accumulation of organic matter, like those occurring in high-mountain environments. The aim of this study was to characterize soils formed in high-mountain environments in the Itatiaia National Park (INP), state of Rio de Janeiro, southeastern Brazil, and to discuss the potential of preserved phytoliths as markers of vegetative history and environmental factors. Four profiles were selected, which were morphologically described and evaluated for their physical and chemical properties. For phytolith analysis and high-resolution determination of the stable carbon isotopes, samples were collected at 0.10 m intervals. The profiles showed highly similar morphological characteristics, with peat deposits and colluvial sediments as source material, produced in the highest parts of the landscape. High-mountain soils in the INP have properties related to high contents of organic matter, like high acidity, low base saturation, and high CEC values due to high H+ contents. The soils are formed by the addition of plant residues, which accumulate due to the cold and humid climate during most of the year in these environments. The phytolith assemblage had a high frequency of morphotypes characteristic of temperate, cold, and high elevation intertropical regions, especially of Pooideae plants. The phytolith indexes indicated open vegetation environments with a predominance of C3 grasses, suggesting cold climate conditions, and corroborating the δ13C isotopic values. The results of phytolith analysis of the profiles reflected characteristics related to soil genesis. Organism is the main soil formation factor, conditioned by the factors relief (elevation) and climate, which resulted in low temperatures and lead organic matter accumulation.

ABSTRACT Although ferruginous materials occur frequently in soils of tropical regions, information about the reversal of the hardening process of these materials is scarce. This study assessed the influence of different chemical treatments and periods of immersion on the reversibility of the hardening process of plinthite and petroplinthite in soils of the Araguaia River plain. Soil samples were collected from the plinthic horizons in 0.10 m high and 0.15 m diameter PVC cylinders and divided into subsamples with a rock hammer. Homogeneous petroplinthite samples were also collected and broken into subsamples with a rock hammer. The plinthite and petroplinthite subsamples were subjected to five immersion treatments: distilled water, calcium carbonate solution, sodium hydroxide solution, sodium hydroxide solution + sodium hexametaphosphate, and acidic solution. The subsamples were immersed for 20, 40, 80, and 160 days. The dispersion and stability degrees and compressive strength in these subsamples were assessed. The wet aggregate stability test indicated no impact on the structural stability of plinthite and petroplinthite subsamples subjected to the treatment with different chemical agents, demonstrating the non-reversibility of the hardening process of these materials of the Araguaia River floodplain, under the studied conditions.

RESUMO A avaliação integrada dos atributos físicos, estoque de carbono (EstC) e de nitrogênio (EstN) além da abundância natural de δ13C do solo se mostram eficazes na detecção de mudanças ocorridas na paisagem. Portanto, o objetivo deste estudo foi avaliar e comparar a densidade do solo, EstC, EstN e abundância natural de δ13C em perfis de solo de diferentes fitofisionomias da Estação Ecológica de Pirapitinga – EEP visando elucidar as mudanças ocorridas nesse ambiente. Para isso, foram coletadas e analisadas amostras de terra em profundidade de até um metro nas diferentes fitofisionomias da EEP. Os maiores teores de argila do solo e densidade de plantas das fitofisionomias florestais proveram maiores EstC e EstN e menores valores de densidade do solo em comparação às demais vegetações campestres. O δ13C revelou que as áreas das fitofisionomias florestais eram antes ocupadas preponderantemente por plantas do ciclo fotossintético C4, semelhantes à vegetação campestre encontrada atualmente na EEP.

ABSTRACT The integrated assessment of physical attributes, carbon (StockC) and nitrogen (StockN) stock, and natural abundance of δ13C are effective in detecting landscape changes. Therefore, this study aimed to evaluate and compare the bulk density, StockC, StockN and natural abundance of δ13C in the soil profiles of different vegetation types of the Pirapitinga Ecological Station (EEP), to elucidate the changes in this area. For this, soil samples were collected and analyzed at depths up to one meter in different vegetation types of the EEP. The highest soil clay content and density of plant of forest vegetation promoted higher levels of StockC and StockN and lower bulk density values than the other grassland vegetation. The δ13C revealed that the areas of forest vegetation types were previously occupied mainly by plants of the C4 photosynthetic cycle, similar to grassland currently found in the EEP.

ABSTRACT The Cerrado is a vegetation complex with a wide variety of phytophysiognomies, and sustainable management is essential for maintaining biodiversity. Morphopedology is a tool that can assist in developing plans for control of soil and land use, especially in evaluating the potential of soil erosion processes. This technique allows landscape units considered “homogeneous” to be distinguished, as a result of interaction between physiographic conditions. The aim of this study was to evaluate potential for erosion in São Miguel do Araguaia, state of Goiás, Brazil, through definition of morphopedological compartments (MPC), on the assumption that soil use has increased erosion. Landscape units were identified through use of geology overlay, hypsometry, slope, geomorphology, soil, and land use. The map information on a 1:100,000 scale was refined, the base of which was available in the Geographic Information System of Goiás. The morphopedological approach enabled identification of five MPC. Predominant soil classes in São Miguel do Araguaia (with matching categories) are Latossolos Vermelho-Amarelo Distróficos (Xanthic Hapludox), Plintossolos Pétricos Concrecionários (Petronodic Haplargids), Plintossolos Háplicos Distróficos (Plinthic Haplaquox), Gleissolos Háplicos Tb Distróficos (Typic Endoaquents), and Neossolos Quartzarênicos Órticos (Typic Quartzipsamments). Generally, every class of soil has some type of limitation that may cause erosion to different degrees. The most dissected areas are associated with lateritic covers, which suggests the importance of these features on topographical formation. The results of analysis of erosion susceptibility and linear erosion potential suggest low risk of erosion, even considering human activities, especially cattle ranching.

ABSTRACT The Bambuí Group, formed from siliciclastic sediments deposited on an extensive epicontinental platform at the end of the Neoproterozoic era, is characterized by limestones with fine to very fine texture. Limestone-derived soils in the southeast of Tocantins state, Brazil, are less notorious than similar soils in other regions of Brazil and their characterization could contribute to the Brazilian System for Soil Classification (SiBCS). Given that little is known of these soils, despitetheir agricultural potential, the objective of this study was to characterize their properties and the processes leading to soil of genesis, and also contribute to developing the Brazilian System of Soil Classification (SiBCS). Soils profiles were located on the summit (P1), shoulder (P2), backslope (P3), and footslope (P4) of a toposequence in the municipality of Lavandeira, Tocantins. Morphological, physical, chemical, and mineralogical properties of the profiles were determined. The soils were classified as: P1 - Chernossolo Rêndzico Lítico típico (Lithic Haplustolls); P2 - Cambissolo Háplico Ta Eutrófico léptico hipocarbonático (Lithic Haplustolls); P3 - Cambissolo Háplico Carbonático léptico (Lithic Haplustepts); and P4 - Luvissolo Háplico Órtico típico (Typic Rhodustalfs). All the profiles showed high contents of silt, calcium, and magnesium, which resulted in high pH and low exchangeable aluminum content. Base saturation and calcium carbonate equivalent contents were also high, and the horizons showed dark colors due to high organic matter content, which contained humin as the dominant fraction. Mineralogical analysis of the clay fraction indicated predominance of hydroxy-interlayered vermiculite, followed by illite, kaolinite, and quartz, whereas the sand fraction exhibited reflections characteristic of the quartz mineral. Given P4 contents of calcium carbonate equivalent above 50 g kg-1 and the relevance of this feature for agriculture, we propose the inclusion of hypocarbonate as a criterion for classification of Luvissolos Háplicos Órticos at the subgroup level.