RESUMO Na região da Serra da Mantiqueira os estudos pedogenéticos podem contribuir tanto para o entendimento de eventos pretéritos como para auxiliar na conservação dos recursos naturais. Este estudo objetivou caracterizar solos de região altomontana de Minas Gerais para avaliar a influência das condições paleoambientais na pedogênese. Cinco perfis foram selecionados e caracterizados quanto aos atributos morfológicos, físicos e químicos. Análises isotópicas de 13C foram realizadas em amostras de solo coletadas nas profundidades de 10, 20, 30, 40, 50, 60, 80 e 100 cm; exceto em P2, que foi coletado até 60 cm de profundidade. A distribuição errática das frações granulométricas e de C evidenciam a natureza sedimentar dos solos, resultado da ação erosiva condicionada pelo relevo. Nos perfis P2, P4 e P5 (Cambissolos/Cambisols) a coloração brunada indica o processo de xantização, enquanto no perfil P1 (Argissolo/Lixisol) é evidenciado o processo de eluviação e iluviação, resultando no incremento de argila em profundidade e pela presença de cerosidade. Em P3 (Latossolo/Ferralsol) os pequenos valores de soma de bases, remoção de sílica e valores da razão SiO2/Al2O3 (índice ki) inferiores a 1,0 evidenciam o intemperismo avançado e o processo de alitização. Nos perfis verifica-se elevados teores de C orgânico em profundidade e acúmulo superficial, o que sugere a ocorrência do processo de melanização. A variação na assinatura isotópica do δ 13C indica uma condição pretérita mais seca, com vegetação mista, com mudança gradual de vegetação com via fotossintética predominante C3. Em P1 e P4, a diminuição dos teores de δ 13C em superfície é resultado da ação antrópica.

ABSTRACT In the Serra da Mantiqueira region the pedogenetic studies contribute to both the understanding of past events and supporting the conservation of natural resources. This study aimed to characterize the soils from the Minas Gerais high-mountains region to evaluate the influence of paleoenvironmental conditions on pedogenesis. Five profiles were selected and characterized for morphological, physical and chemical properties. Isotopic analyses of 13C were performed in soil samples collected at depths of 10, 20, 30, 40, 50, 60, 80 and 100 cm; except in P2, which was collected up to 60 cm deep. Erratic distribution of the particle-size fractions and C contents highlight the sedimentary nature of the profiles, resulting from the erosive action favored by the relief. High organic C content in subsurface and its accumulation in the surface were observed in the profiles, which suggests the occurrence of the melanization process. In the profiles P2, P4 and P5 (Cambissolos/ Cambisols) the brownish color indicates the xanthization process, while in P1 (Argissolo/ Lixisol), is highlighted the process of eluviation and illuviation resulting in the increase of clay in subsurface and presence of clay films. In P3 (Latossolo/ Ferralsol), the low values of sum of bases, silica removal and SiO2/Al2O3 ratio (ki index) values below 1.0 point to the advanced weathering and the allitization process. The variation in the isotopic signature of δ13C indicates a drier past condition, with mixed vegetation, with gradual change of vegetation with predominant C3 photosynthetic pathway. In P1 and P4, the decrease in the contents of δ13C in surface results from anthropic action.

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.

RESUMO O intemperismo do material de origem é o processo inicial que garantirá ao solo maior ou menor fertilidade, tornando o estudo desse processo fundamental para entender a dinâmica do solo. Grande parte dos estudos de intemperismo é baseada em índices que calculam a taxa de dissolução dos feldspatos (CIA, CIW e PIA, por exemplo) muitas vezes não refletindo a complexidade do intemperismo ocorrendo no perfil de solo. Outras metodologias- como balanço geoquímico, diferença elementar (DE) e índice W- têm sido desenhadas para melhorar esses estudos. Avaliar se essas metodologias serão mais eficientes que os índices CIA, CIW e PIA para apontar as variações intempéricas em perfis recentes desenvolvidos de basalto é o objetivo desse trabalho. Foram utilizados dados de óxidos principais para calcular o balanço geoquímico, DE, CIA, CIW, PIA e W e analisar a intensidade do intemperismo em dois perfis originados de basalto no Estado de São Paulo. Foram fatorados também os índices Ki e Kr e a relação Fe o/Fed e analisada a mineralogia dos horizontes dos solos e da rocha de origem. O índice W e a DE mostraram maior variação intempérica que CIA, CIW e PIA. O balanço geoquímico, a mineralogia e as razões Ki e Kr, Feo /Fed foram eficientes em explicar as variações que ocorreram entre os horizontes. A junção da DE com o balanço geoquímico trouxe novas informações para a análise do intemperismo que a observação isolada de CIA, CIW e PIA.

ABSTRACT Weathering of the parent material is the initial process that plays an essential role in soil fertility. The study of this process has become crucial to better understand soil dynamics. Most studies on weathering are based on indexes that calculate the feldspar dissolution rate (for example, CIA, CIW, and PIA) which not always reflect the complexity in the soil profile. Other methodologies have been designed to improve these approaches, such as geochemical balance, difference of elemental contents (DE), and the W index. This work aim to assess the efficiency of these methods to identify variations in recent soil profiles developed from diabase as compared to the CIA, CIW, and PIA indexes. Data on the main oxides were used to calculate the geochemical balance, DE, CIA, CIW, PIA, and W indexes to analyze weathering intensity in two profiles originated from diabase in the São Paulo State, Brazil. The Ki and Kr indexes and Feo /Fed ratio were also factored and we analyzed the mineralogy of soil horizons and the source rock. The W index and DE presented greater weathering variation than the CIA, CIW, and PIA in both profiles. The geochemical balance, mineralogy, and the Ki, Kr and Feo /Fed ratios explained the variations between the horizons. The DE and geochemical balance together generated new information for the analysis of the weathering process than the isolated indexes.

Resumo O objetivo deste trabalho foi analisar as modificações mineralógicas, morfológicas e composicionais resultantes do intemperismo de grãos de diabásio enterrados em solo sob diferentes usos da terra por até 378 dias. Amostras de diabásio cominuído foram colocadas em sacos de poliéster e enterradas em solo sob cultivo de milho, capim-elefante e floresta, tendo sido desenterradas e avaliadas após quatro períodos. As amostras do remineralizador (RM) foram analisadas por difratometria de raios X, análise química total, microscopia eletrônica de varredura, e teores de Al (Ald e Alo) e Fe (Fed e Feo) extraídos com soluções de ditionito-citrato-bicarbonato (DCB) e amônio oxalato (AAO). Os plagioclásios e os piroxênios intemperizaram mais rápido nos três tipos de uso da terra, e mostraram o mesmo padrão de ganhos e perdas no balanço de massa de elementos. A caracterização das formas de Fe e Al em DCB e AAO mostrou que a maior mudança destes elementos foi da fase litogênica e cristalina para a secundária e amorfa, em comparação aos seus teores totais. Os plagioclásios e os piroxênios foram os minerais mais alterados, e Fe e Al apresentam grande transferência entre a fase cristalina e amorfa, com valores de até 26 e 175, respectivamente, para as razões entre sacos com RM/Feo e RM-controle e sacos com RM/Alo e RM-controle.

Abstract The objective of this work was to analyze the mineralogical, morphological, and compositional modifications resulting from the weathering of diabase grains buried into soil under different land uses for up to 378 days. Samples of comminuted diabase were put into polyester bags and buried into soil under corn crop, elephant grass, and woods, being unburied and evaluated after four time periods. The samples of the remineralizer (RM) were analyzed by X-ray diffractometry, total chemical analysis, scanning electron microscopy, and Al (Ald and Alo) and Fe (Fed and Feo) contents extracted by sodium dithionite-citrate-bicarbonate (DCB) and ammonium oxalate (AAO) solutions. Plagioclases and pyroxenes were the most weathered minerals in all three land uses and showed the same pattern of elemental gains and losses. The characterization of Fe and Al solubility in DCB and AAO showed that the greatest change in these elements was from the lithogenic and crystalline to the pedogenic and amorphous phase, when compared with their total content. Plagioclases and pyroxenes were the most weathered minerals, and Fe and Al show a great transfer from the crystalline to the amorphous phase, with values up to 26 and 175, respectively, for the ratios between bags with RM/Feo and RM-control and bags with RM/Alo and RM-control.

ABSTRACT Lithological and geomorphological variations determine formation of soils with different mineralogical constitutions and can influence the distribution of potentially toxic elements (PTE). The aim of this study was to determine the contents of PTE and mineralogical assemblages along soil profiles of different classes and parent materials and to investigate the association among these factors in the São Francisco sedimentary basin in the northern part of the state of Minas Gerais (Brazil). Eight soil pedons of different classes that developed from different parent materials (limestone, siltstone, phyllite, alluvial-colluvial sediments, detrital cover, and rhythmite) were studied in two lithotoposequences. Soil morphological, particle-size, and chemical analyses were carried out for soil characterization and classification. A mineralogical investigation was carried out by X-ray diffraction on soil sand, silt, and clay fractions. Potentially toxic elements were extracted by microwave-assisted acid digestion (EPA 3015A method) and determined in an ICP-OES. Soil mineralogy showed relevant interactions between pedogenesis and morphogenesis. Quartz is the main mineral in the sand and silt fractions, with varying amounts of weatherable primary minerals, whereas kaolinite is the main mineral in the clay fraction, followed by 2:1 clay minerals and oxides. The main soil properties associated with PTE variability were pH, redox environment, mineral and organic reactive surfaces, and clay content. The unique patterns of PTE distribution per pedon and differences in PTE contents in soils from the same parent material, but with different pedogenic evolution, showed that pedogenic processes influence PTE distribution. Mainly Mn, Ni, Pb, and Ba were influenced by parent material, especially limestone, siltstone, and detrital cover, but Cd, As, and Cu were also influenced. To a lesser extent, Mo was influenced by phyllite and Cr by detrital cover and phyllite. Rhodic Ferralsol (Latossolo Vermelho Distrófico típico) was the only taxonomic class to show class association with PTE. The association of Ferralsols (Latossolos) with Cd, Mn, Ni, Pb, Ba, As, and Cu and the low contents of these elements in soils of this class suggest that pedogenic processes common to Ferralsol (Latossolo) evolution are responsible for decreasing levels of these PTE.

RESUMO: O uso de remineralizadores como insumo agrícola foi regularizado em 2013, mas seus mecanismos de ação precisam ser melhor conhecidos para viabilizar o manejo nos campos agrícolas. Atributos químicos de um Latossolo foram monitorados após remineralização com diabásio. O aumento de Na trocável foi atribuído à dissolução das bordas dos plagioclásios (albita) onde a concentração deste elemento é maior. Infelizmente, não é possível especular se o tempo decorrido desde a aplicação (um a dois anos, dependendo do tratamento) foi suficiente para solubilizar o núcleo cálcico (anortita) destes cristais, já que o remineralizador possui outros minerais fonte de Ca. Houve aumento da capacidade de troca catiônica efetiva sem aumento do pH. As hipóteses propostas para explicar este fenômeno são a precipitação de fases oxídicas amorfas e o aparecimento de cargas elétricas na superfície dos grãos do remineralizador durante sua dissolução. Apesar da concentração de Al2O3 do remineralizador (11,90%) e Fe2O3 (14,45%), não houve aumento destes elementos no complexo de troca, possivelmente por sua rápida precipitação em formas amorfas (Alo e Feo no solo).

ABSTRACT: Remineralizers are comminuted rocks that are applied to soil, and their use as an agricultural amendment was regulated in Brazil in 2013. However, mechanisms of action of these materials must be better known to enable them to be best used in agricultural fields. Soil chemical attributes of an Oxisol were monitored after the application of a diabase remineralizer. The increase in exchangeable Na observed was associated with the dissolution of the border of the plagioclase crystals where this element is highly concentrated (albite). Therefore, it was inferred that the time since the application of the remineralizer (1 to 2 years depending on the treatment) was not sufficient to exhaust this crystal volume. Unfortunately, the presence of several sources of Ca-containing minerals in the remineralizer did not allow to infer if the calcic nuclei was dissolving. An increase in effective cation exchange capacity was observed without the concurrent increase in the pH of the soil. The two non-exclusive hypotheses proposed to explain this result were that an extra surface charge has originated on the surface of the newly precipitated oxidic phases and/or from the dissolution of the remineralizer grains. Rapid precipitation of amorphous solids (as measured by the increase in Alo and Feo) would also explain the lack of increase in exchangeable Fe and Al despite the large amount of Al2O3 (11.90%) and Fe2O3 (14.45%) in the remineralizer.

Resumo O objetivo deste trabalho foi avaliar diferentes estratégias para a predição da distribuição de classes de solo em mapas pedológicos digitais de áreas sem dados de referência, na bacia sedimentar do São Francisco, no Norte de Minas Gerais. As estratégias incluíram: o detalhamento da legenda, o treinamento por observações em campo, a ampliação do conjunto de treinamento e o uso de diferentes algoritmos de mineração de dados. Foram elaboradas quatro matrizes, diferenciadas pelo volume de dados, para o aprendizado dos algoritmos, e pelo nível taxonômico das classes de solo a serem preditas. Avaliou-se o desempenho dos algoritmos de aprendizado de máquina - Random Forest, J48 e MLP -, associados a procedimentos de discretização, balanceamento de classes, seleção de variáveis e expansão do conjunto de treinamento. O balanceamento de classes, a discretização de variáveis por frequências iguais e o algoritmo Random Forest apresentaram os melhores desempenhos. A extensão da representatividade das observações em campo, que presume uma área de treinamento mais ampla, não trouxe ganho preditivo. A generalização taxonômica para subordem diminui a fragmentação dos polígonos mapeados e aumenta a acurácia dos mapas pedológicos digitais. Quando são produzidos após treinamento por observações de solo in situ, na área de mapeamento, os mapas pedológicos digitais têm valores de acurácia equivalentes aos dos treinados em mapas preexistentes.

Abstract The objective of this work was to evaluate different strategies for the prediction of soil class distribution on digital soil maps of areas without reference data, in the sedimentary basin of San Francisco, in the north of the state of Minas Gerais, Brazil. The strategies included: taxonomic generalization, training by field observations, training set expansion, and the use of different data mining algorithms. Four matrices were developed, differentiated by the volume of data for machine learning and by soil taxonomic levels to be predicted. The performance of the machine learning algorithms - Random Forest, J48, and MLP -, associated with discretization, class balancing, variable selection, and expansion of the training set was evaluated. Class balancing, variable discretization by equal frequencies, and the Random Forest algorithm showed the best performances. The representativeness extension of field observations, that assumes a larger training area, brought no predictive gain. Soil taxonomic generalization to the suborder level reduces the fragmentation of mapped polygons and improves the accuracy of digital soil maps. When generated by training on in situ soil observations at the mapping area, digital soil maps are as accurate as those trained on preexistent maps.