ABSTRACT There has long been a discussion about the effects of soil management on its structure. Since changes can occur due to management and time of use, more accurate assessments can be achieved if carried out in long-term experiments. This study investigated the long-term effects of soil management on the physical quality of a Cerrado Oxisol (Latossolo Vermelho), focusing on microstructural changes. Micromorphology and computed tomography techniques were used to assess the soil's microstructure. The study compared areas under long-term and different soil management practices, including disc plowing, no-tillage, and disc harrow+subsoiler. A native Cerrado area was considered as the reference. Micromorphology revealed some changes in the pedological features of soil aggregates, but the granular structure showed good resistance even after two decades of use and management. It also indicated a decrease in larger pores and an increase in the surface soil layer micropores for the disc plowing and no-tillage treatments. These results were consistent with traditional laboratory evaluations of soil porosity. Computed tomography was limited due to increased soil bulk density in the cultivated treatments, but it showed potential for assessing soil porosity and pore connectivity. We concluded that micromorphology effectively identifies microstructural changes in Oxisols with small and strong granular structures, and the granular soil aggregates displayed resilience even after long-term management. The micromorphometric evaluation corroborates with traditional methods and suggests loss of pores associated with the disc harrow+subsoiler treatment.

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 The geochemical behavior of the major, minor, trace and rare earths elements (REEs) in soil profiles from ultramafic volcanoclastic rocks of the Vulcão do Paredão and Morro Vermelho Formation from Trindade Island (TI) was analyzed in this study. Losses and gains of chemical elements were calculated through the mass balance for two profiles along the slope: one located at higher altitude (460 m) and the other at lower altitude (258 m). In all profiles, Al, Fe and Ti accumulate due to their low mobility, whereas Ca, Na, K and Mg are the most intensely leached. Soils located at lower altitude show higher K and Mg values in the surface due to the contribution of saline sprays. Leaching of the REEs from higher to the lower slope led to the enrichment of these elements, especially the light REEs, in the soil at the lowest altitude (258 m). The high altitude profile showed Ce positive anomaly due to longer exposure to weathering. The geochemical balance shows a relative enrichment of Ti, Mn, Fe, Co, Cr, Ni, V, Zr, S related to the loss of mobile elements during the soil formation process, despite the youthful nature of these volcanic rocks.

ABSTRACT The pedological studies carried out so far in Trindade Island (TI) have obtained patchy evidences of allophane, without detailed mineralogical and micromorphological studies to confirm the occurrence of Andosols in TI. Therefore, in this study, the mineralogical, micromorphological, physical and chemical characterization of four soil profiles from Vulcão do Paredão (P1) and Morro Vermelho formations (P2, P3, and P4) were carried on the latest volcanic events in Brazil from Trindade Island (TI) with the aim of to evaluate the presence of Andosols in this oceanic island. Profiles P1 and P2 are developed on pyroclastic bombs, and show, respectively, A-Bi- C and decapitated A-C horizons, whereas P3 and P4 are developed on lapillitic and bomb pyroclasts, show A-C horizons. The soil profiles have a reddish and brownish clayey matrix, are highly friable and show a plastic consistency. Their microstructures are granular, single grain and intergrain microaggregate, in which aggregates display an undifferentiated b-fabric. The mineralogical constituents of the bulk fraction are biotite, hematite, magnetite, ilmenite, pyroxene, olivine, halloysite, goethite, anatase, and rutile. The clay fraction is marked by the presence of halloysite, ferrihydrite, and little amounts of allophane. All soils presented andic properties and can be classified as non-allophanic Andosols. In addition, micromorphological features closely resemble those reported in Andosols from other volcanic islands from elsewhere. The predominance of halloysite in the clay fraction formed by alteration of sideromelane, suggests that allophane would be an intermediate phase of this rapid transformation favored by the wet climate conditions of the highest parts of TI.

RESUMO Os solos da região semi-árida de Minas Gerais possuem pequena profundidade; consistência dura, muito dura ou mesmo extremamente dura quando seca e muito plástica e muito pegajosa quando úmida; estrutura colunar ou em blocos angulares e fendilhamento significativo ao longo do perfil no período seco, entretanto eles não foram profundamente estudados até agora. Assim, o objetivo deste estudo foi detalhar a gênese dos Luvissolos da Depressão Semi-árida do Vale do Jequitinhonha (MG), a partir de atributos morfológicos, físicos, químicos, micromorfológicos e mineralógicos, e suas relações. A ausência de cutãs de iluviação na análise micromorfológica em laboratório foi consistente com a fraca e pouca cerosidade observada no topo do horizonte B de apenas um dos quatro perfis de solo estudados durante os trabalhos de campo. Considerando a ocorrência de argilominerais 2:1 expansíveis, os quais podem facilmente modificar tal feição pedológica, cautela é recomendada com relação à interpretação da gênese do solo. Desta maneira, a perda lateral de argila dos horizontes superficiais é enfatizada como o principal processo de formação dos Luvissolos estudados. A capacidade de troca de cátions desses solos revelou valores diferencialmente mais baixos para Luvissolos em regiões semi-áridas brasileiras.

ABSTRACT Soils of the semi-arid region of Minas Gerais have small depth; hard, very hard or even extremely hard consistency when dry and very plastic and very sticky when moist; columnar or angular blocky structure and significant cracking along the profile in the dry period, however they have not been deeply studied yet. Thus, the aim of this study was to detail the genesis of Luvisols in the Semi-arid Depression of the Jequitinhonha Valley (MG), incompassing morphological, physical, chemical, micromorphological and mineralogical attributes, and their relationships. The lack of illuviation coatings in the micromorphological analysis is in line with the expressionless and unclear clay skins observed in the top of the B horizon in only one out of the four soil profiles during the field work. Considering the occurrence of expandable 2:1 clay minerals, which can easily modify such pedological feature, caution is recommended in relation to soil genesis interpretation. The lateral loss of the clay fraction from the superficial horizons is highlighted as the main formation process of the Luvisols studied. The cation exchange capacity of these soils revealed remarkable lower values for the Luvisols in semi-arid Brazilian regions.

ABSTRACT: Currently, the Brazilian savanna (Cerrado) represents the main agricultural area of the country, comprising a great variety of landscapes and soils, geological formations and vegetation patterns, as well as the major watershed. We studied the hydropedology and morphometry of a representative catchment (Frutal river), on a high tableland (Chapada) in the Triângulo Mineiro region, Brazil, describing the soil-water-landscape relationships to understand land use and water resources. To this end, we applied physical, chemical, micromorphological, and morphometric methods. When dry, compaction was observed in well-structured Ferralsols (Latossolos) with medium texture under intensive agriculture, reducing the water recharge capacity. The soil carbon stock was highest in hydromorphic savannas (veredas), reaching an organic matter content of 316.8 g kg-1 in the studied Umbric Gleysols, representing poorly drained lowlands. Physical and micromorphological properties were relevant parameters to understand the water recharge in soil; in agricultural fields, bulk density tended to increase and hydraulic conductivity to decrease, particularly under long-term sugarcane; morphometric parameters in the Frutal catchment indicated a low flooding risk and high flow capacity. This reinforces the need for soil conservation strategies to enhance water infiltration and groundwater recharge, with a view to maintain the water longer in the catchment. For surface water dynamics, slope morphology is an important property, affecting soil erosion, water retention and crop productivity.

ABSTRACT Although the physical environment of the Atlantic Forest realm is well known, studies on the soil-landform relationships are fundamental to improve the management of soil resources to facilitate sustainable development. The purpose of this study was to evaluate a representative topossequence on the “Mares de Morros” landscape of deeply weathered regolith on leucocratic granite rocks and demi-orange convex slopes. The soils varied along the topossequence according to drainage and were classified as Acrudox, Pseudogleysol, and Epiaquent. The clay fraction was composed by kaolinite, in association with gibbsite, goethite, hematite, and traces of vermiculite and hydroxy-Al interlayered vermiculite (HIV). The kaolinite crystallinity index obtained by different methods showed high structural disorder throughout the sequence, indicating that long-term pre-weathering has produced a homogenous regolith with little differences in terms of mineralogy, despite the changes in drainage. On the other hand, micromorphological features showed a complete change from the typical, well-developed microaggregate structure of upland, well-drained soils, to a massive, poorly developed structure downslope, consistent with the morphological description. Changes in microstructure development and micropedological features occurred both vertically and laterally along the topossequence and indicate that mineralogy alone cannot account for the microaggregate structure of kaolinitic Latossolos (Oxisols) well-drained with low Fe contents. Soils from the “Mares de Morros” landscape of the Alegre river basin on leucocratic granitic rocks highlight an inheritance of a deep pre-weathered regolith, showing subtle chemical and mineralogical changes, but marked morphological and physical differences along the topossequence, basically controlled by soil drainage in the past or present.

ABSTRACT Pedological studies using X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, and scanning electron microscopy (SEM-EDS) showed a Xanthic Ferralsol formed from the degradation of bauxite on a slope in the Caparaó region, in southeastern Brazil. We found a decrease in the number and size of bauxite fragments toward the top of the profiles, bauxite fragments that were more degraded at the top of the profiles, transformation of gibbsite into kaolinite, and absolute enrichment in silicon in the mass balance. These indicators suggest that resilication could be the major process responsible for formation of the soil; detailed studies are needed to verify the origin of the silica. The reintroduction of silica into the system occurs by the biogeochemical cycling of vegetation and, in some cases, water table fluctuations, highlighting the role of resilication as a soil-forming process in bauxite-derived soils.

Resumo O Sinclinal Moeda, localizado nas terras altas do Quadrilátero Ferrífero (SE do Brasil), se insere em um ambiente de inversão do relevo e de reorganização da drenagem. Neste trabalho foram analisadas as bacias do Rio do Peixe e Ribeirão Mata Porcos, que drenam o Sinclinal. Foram realizados procedimentos de análise morfológica e morfométrica em geoprocessamento. Os resultados indicam que o Ribeirão Mata Porcos teria sido capturado primeiro, permitindo o avanço da onda de incisão que denudou a bacia e rebaixou o nível de base. Em uma última fase de capturas, teria ocorrido a reversão da drenagem de alguns canais e a geração de cotovelos. Ao longo destes eventos ocorreu a migração preferencial dos canais fluviais em direção a leste e o pirateamento de águas subsuperficiais e a decapitação (beheading) de parte da bacia do Rio do Peixe. Baseado nestas análises e em dados da literatura, acredita-se que os eventos geomorfológicos responsáveis pela evolução do Sinclinal Moeda durante o Quaternário estiveram associados, sobretudo, a capturas fluviais (sensu strictu, diversion e beheading) controladas por causas neotectônicas e litoestruturais.

Abstract The Moeda syncline, located in the highlands of the Iron Quadrangle mountains (SE Brazil), is a setting of relief inversion and drainage reorganization. In this work, we investigate the Rio do Peixe and Ribeirão Mata Porcos watersheds from this syncline. Morphological and morphometric analyses were carried out on GIS environment. The results indicate that the Ribeirão Mata Porcos watershed was captured first, allowing a wave of incision propagation that denuded the watershed and lowered the base level. During the last phase of river capture, drainage reversal and elbows of capture developed in certain channels. During these events, there was a preferential migration of river channels to the east, groundwater piracy and beheading of the Rio do Peixe's area. Based on such results, we believe that the events responsible for the landscape evolution of the Moeda syncline during the Quaternary were particularly those associated with river capture (sensu strictu, diversion and beheading) driven by both neotectonics and litho-structural influences.

Resumen El Sinclinal Moeda, ubicado en las tierras altas del Cuadrilátero Ferrífero (sureste de Brasil), presenta características de inversión de relieve y reorganización de drenaje. En este trabajo, las cuencas del Rio do Peixe y Ribeirão Mata Porcos fueron analizados. Se llevaron a cabo análisis morfológico y morfométrico por medio de SIG. Los resultados indican que el Ribeirão Mata Porcos ha sido capturado primero, permitiendo el avance de la onda de incisión que denudó la cuenca y rebajó el nivel de base. En una última fase de las capturas, se han producido la reversión de algunos canales de drenaje y la generación de codos fluviales. A lo largo de estos hechos ocurrieron la migración preferente de canales fluviales para la dirección este, el pirateamento de las aguas del subsuelo y la decapitación de parte de la cuenca del Rio do Peixe. Basándose en estos resultados, se cree que los eventos responsables por la evolución del Sinclinal Moeda durante el Cuaternario estaban relacionados, sobretodo a las capturas fluviales (sensu strictu, diversion y beheading) controlado por causas neotectónicas y litoestructurales.

RESUMO A área de estudo que se situa na borda oeste do Planalto do Espinhaço Meridional, na qual predominam as rochas siliciclásticas que integram unidades geológicas diversas, observaram-se dois tipos distintos de padrões de distribuição da formação superficial, linear e zonal. Este trabalho objetiva analisar essa distribuição espacial das formações superficiais de trecho do Planalto do Espinhaço Meridional localizado no alto curso do Rio Pardo Pequeno (MG), discutindo o papel exercido pela organização litoestrutural na espacialidade dessa cobertura pedológica. Para executar tal investigação foram produzidos mapas de distribuição espacial das formações superficiais, mapa de estrutura geológica, e perfis topográficos e geológicos. As formações superficiais verificadas na área de estudo apresentam uma distribuição espacial essencialmente conduzida pelas características do arcabouço estrutural e litológico da região. A distribuição linear relaciona-se às feições estruturais, como: falhas, falhas de empurrão, alinhamentos, anticlinais e sinclinais. Já as formações zonais são influenciadas pelas diferenças entre a resistência das diversas rochas aos processos intempéricos. O estudo das características das formações superficiais e suas associações com os aspectos litoestruturais são essenciais para compreender a configuração geomorfológica do alto curso do Rio Pardo Pequeno.

ABSTRACT The study area which lies on the western edge of the Southern Highlands Ridge, are predominant in siliciclastic rocks that integrate different geological units, we observed two distinct types of distribution patterns of shallow, linear and zonal training. This work aims to analyze the spatial distribution of surface formations stretch from the Southern Espinhaço Plateau located in the upper reaches of the Rio Pardo Small (MG), discussing the role played by the organization in litoestrutural spatiality of this soil cover. To perform such an investigation of spatial distribution maps of surface formations, geological structure map, and topographical and geological profiles were produced. The superficial formations observed in the study area have a spatial distribution essentially driven by the characteristics of the lithological and structural framework of the region. The linear distribution is related to structural features, such as faults, thrust faults, alignments, anticlines and synclines. Already zonal formations are influenced by differences between the resistance of different rocks to weathering processes. The study of the characteristics of surface formations and their associations with lithostructural aspects are essential to understand the geomorphic setting of the upper reaches of the Rio Pardo Small.

No Arquipélago de São Pedro e São Paulo, a deposição de excrementos da avifauna foi responsável pela fosfatização de suas rochas. Como feição mais característica, formaram-se crostas fosfáticas. Com base em metodologias pertinentes ao trabalho de campo (observação, descrição e coleta) e de laboratório (análises geoquímicas, mineralógicas e microscópicas), esse trabalho buscou caracterizar tais crostas e compreender suas implicações geomorfológicas e paleogeográficas. As crostas foram definidas como feições de acumulação de excrementos, ricos em fósforo, mineralizados sobre rochas homogêneas (peridotitos milonitizados). Depois de formadas, o comportamento hidrofóbico de tais crostas protegeu as rochas contra o avanço acelerado do perfil de alteração e da atuação de processos erosivos, tornando as encostas em que são encontradas mais íngremes e convexizadas. Ao contrário, onde a formação da crosta não foi verificada, as encostas encontram-se concavizadas e a rocha mais profundamente alterada. A presença de tais crostas também indica a existência de ambientes áridos pretéritos, diferentes das condições climáticas atuais, onde foi possível a acumulação do guano sobre a superfície.

In the São Pedro and São Paulo Archipelago, deposition of bird excrements has been responsible for rock phosphatization, generating phosphatized crusts. This study describes these crusts and establishes their geomorphological and paleogeografical implications, based on methodologies such as field observation, description and sampling, as well as, laboratorial analyses (geochemical, mineralogical and microscopic). The crusts were defined as features of excrement accumulation, with high P content and mineralized surfaces over homogeneous rocks (milonitizaded peridotites). The hydrophobic behavior of these crusts protects the underlying rock against the accelerated advance of chemical weathering and, consequently, the role of erosion processes, developing steeper and more convex slopes. In contrast, at sites in which the formation of the crust has not been verified, the rock is more weathered and the slopes more concave. The presence of these crusts also indicates an arid paleo-environment, where guano accumulation was possible, differently from present-day climate conditions.