ABSTRACT Soils in the Depressão Central and Campanha Gaúcha in Rio Grande do Sul State, Brazil, developed from sedimentary rocks are mainly Alfisols (Luvissolos, Planossolos and Plintossolos) and Ultisols (Argissolos) with high textural contrast between A and/or E horizons and clayey B horizons. Red Ultisols dominate in well-drained areas in the summit. But many soils present redoximorphic features on the backslope and footslope, with mottled and/or nodules similar to plinthite due to the oscillating of the water table above the rock or poorly permeable saprolite. Identifying morphological features, mineralogical and chemical properties, and parent material differences are essential to identify the main processes responsible for their genesis. Knowledge of the relative distribution of different forms of iron in the soil is also of particular interest when interpreting pedogenesis. This study aimed to evaluated the main process responsible for the high textural contrast in soils developed from different sedimentary lithologies, and how the redoximorphic features observed in some soils may be related to genesis of plinthites and ferrolysis processes. The study area is located in the hydrographic basin of Rio Santa Maria, in the city of Rosário do Sul – RS, Brazil (30° 15’ 28” S and 54° 54’ 50” W), average altitude of 132 m and Cfa-type climate. Topolithosequences were defined based on soils developed from lithogies of Piramboia and Sanga-do-Cabral geological formations, by choosing soil profiles according to the source material, variations in relief, altitude and hydrological conditions. Morphological descriptions, particle size determinations, chemical analysis, mineralogy of the clay fraction by XRD analysis, determination of the main forms of iron, tests to identify plinthite were performed. Argiluviation, ferrolysis and plinthization were the most active processes identified in the genesis of most studied soils. The high textural contrast on these soils was not solely due to clay illuviation processes but also ferrolysis and lithological discontinuities in some soils, indicating polygenetic origin. Redoximorphic features in most soil revealed that iron segregation in most soils occurs like mottles and not plinthite, since they did not remain aggregated after the various wetting and drying cycles.

ABSTRACT The source material is one of the factors that most influence soil genesis and the mainly responsible for the nature, composition, and behavior of the soil. Given the geological complexity of the Santa Maria River basin, the objective of this study was to investigate whether the new lithologies described recently may be responsible for a greater variation in soil properties, as well as in the soil taxonomy itself. The study area is located in the municipality of Rosário do Sul, RS, Brazil at 30° 15’ 28” S and 54° 54’ 50” W, with average altitude of 132 m and climate type Cfa. This study was supported by a cartographic base composed of topographic charts, geological maps, satellite images, digital elevation models, and maps of geomorphometric variables, with the support of GPS receivers and GIS. Topolithosequences were defined from soils developed from the Pirambóia, Sanga-do-Cabral, and Guará Formations, and soil profiles were chosen based on types of source materials, variations in relief, and altitude. A classical model of slope compartmentalization was applied for correlation of the geomorphic surfaces with pedogenesis. Soil profiles were described in a general and morphological manner, and soil samples were collected for analysis. The physical and chemical properties determined were particle size, active and potential acidity, organic C content, Ca2+, Mg2+, K+, and Al3+. The sum of bases, CEC, flocculation activity and degree of flocculation of the clay fraction, and base (V), aluminum (m), and sodium saturation were calculated. Soil properties were evaluated through factor analysis and grouping, which allowed profiles to be grouped based on their variables and identification of which variables were preponderant in distinguishing them. Furthermore, multivariate analysis allowed statistical differentiation of the profiles in the same lithostratigraphic unit and in different relief positions, and also differentiation of soils developed from different source materials and occupying similar positions in the pedo-landscape, through the formation of homogeneous groups of profiles linked by their degree of similarity.

ABSTRACT Quali-quantitative and crystallographic characterizations of the different minerals of a soil are essential for the best evaluation of its genesis, degree of weathering, active pedogenetic processes, physical and chemical properties, and its potential reserve of mineral nutrients. This study presents the results of mineralogical investigations carried out to verify the influence of the different lithologies of three geological formations of a sedimentary nature on the mineralogical composition of the soils and the relation of this mineralogical composition to soil chemical properties. The study area is located in the physiographic region of the Santa Maria River basin in the municipality of Rosário do Sul, RS, Brazil, at 30° 15’ 28” S and 54° 54’ 50” W, with average altitude of 132 m and Cfa climate type. Topolithosequences were defined from soils developed from the lithology of the Pirambóia, Sanga-do-Cabral and Guará Formations, choosing representative soil profiles based on types of parent materials and variations in relief and altitude. A general and morphological description of the profiles was carried out, and soil samples were collected for analysis. The properties determined were texture, active and potential acidity, organic C, exchangeable Al, sum of bases, CEC at pH7, and base saturation. Mineralogical characterization of the clay fraction was performed by an X-ray diffractometer (XRD). In most of the profiles, kaolinite was the predominant clay, along with a significant contribution from 2:1 clay minerals and the presence of interstratified minerals in combination with kaolinite, which were related to the chemical properties of the soils. The crystallographic parameters of the kaolinite (full width at half maximum - FWHM, layer-d spacing, mean crystallite size - D, and mean number of layers - NL) varied, revealing a distinct pedogenetic evolution, which can be attributed to different degrees of weathering, as well as differences in the source material. Large and asymmetrical reflexes related to the d001 and 002 planes of kaolinite indicated that they are due to the presence of kaolinite-smectite strata in association with pure kaolinites.

Em um levantamento pedológico, a descrição detalhada do conjunto de atributos do solo é fundamental para se analisar e compreender as interações dos diversos processos que ocorrem no solo. Para tanto, a análise multivariada pode ser uma ferramenta estatística importante para interpretar e compreender melhor as relações e semelhanças entre pedons. Os objetivos deste trabalho foram diferenciar e agrupar pedons similares com base em atributos físicos e químicos usando a estatística multivariada. O estudo foi desenvolvido em Lages, SC, a 27º 48′ de latitude sul e 50º 20′ de longitude oeste, com 916 m de altitude média e clima mesotérmico úmido com verões frescos (Cfb). Sete pedons de Cambissolos desenvolvidos de siltito foram descritos e coletados em um levantamento detalhado de solos para o planejamento conservacionista com base na capacidade de uso das terras. Os atributos químicos e físicos analisados foram textura, densidade, porosidade, estabilidade de agregados em água, teores de carbono orgânico, P, Al, K, Na, Ca, Mg e acidez ativa e potencial. As variáveis de solo foram avaliadas por meio da análise de fatores e agrupamentos. A partir dessas análises, foi possível agrupar os pedons com base em seus atributos químicos e físicos e identificar aqueles que foram determinantes na discriminação dos pedons. Além disso, levou a uma melhor compreensão da natureza intrínseca de correlações entre os atributos físicos e químicos do solo, demonstrando que a análise multivariada é uma ferramenta eficaz no estabelecimento dos agrupamentos de solos.

In a soil survey, a detailed description of a set of soil properties is important for analyzing and understanding the interactions of several soil forming processes. Thus, multivariate analysis may be an important statistical tool to better interpret and understand the relationships and similarities between pedons. The aim of this study was to differentiate and group similar pedons based on physical and chemical properties using multivariate statistics. The study was carried out in Lages, SC, Brazil, at 27º 48' S latitude and 50º 20' W longitude, with an average altitude of 916 m and a humid mesothermal climate. Seven Inceptisol pedons developed from siltstones were described and collected in a detailed soil survey for conservation planning, based on land use capability. The chemical and physical properties analyzed were particle size, bulk density, porosity, aggregate stability in water, organic carbon content, P, Al, K, Na, Ca, Mg, and active and potential acidity. Soil variables were evaluated using factor and cluster analysis. From these analyses, it was possible to group the pedons based on their chemical and physical properties and identify which of them were determinant in discriminating these profiles. Thus, it was possible to better understand the intrinsic nature of correlations between physical and chemical soil properties, demonstrating that multivariate analysis is an effective tool in establishing these soil groups.