mineralogy. Actually, the types of microgranular structure appeared to be mainly related to soil bioturbation by termites and eventually secondarily by ants. Thus, the weak macrostructure and strong microgranular structure of the Latosols studied, the little vertical differentiation of the horizons, and the lack of a clear relationship between their landscape position and parent material characteristics would result from long-term biotic action with high probability.

Mineralogy of the Latosols of the Brazilian Central Plateau remains under discussion in the absence of clear relationship with their age according to their geomorphic location. The aim of this study was thus to clarify the origin the kaolinite and gibbsite content variation by studying a regional toposequence and using data from the literature. Chemical composition and soil color were used to discuss mineralogy. The mineralogy of the clay fraction was also 2 discussed by using X-ray diagrams. Our results showed, that the large variation of kaolinite and gibbsite content can be explained by taken into account both their local and regional location, the variation of the hematite and goethite content remaining limited. The model that is proposed to explain such a variation combines a regional component which is mainly associated to the age of the geomorphic surface and a local component which is mainly associated to the hydraulic conditions along the toposequence.

Abstract:Remote sensing has been used in karst studies to identify limestone terrain, describe exokarst features, analyze karst depressions, and detect geological structures important to karst development. The aim of this work is to investigate the use of ASTER-, SRTM-and ALOS/PRISM-derived digital elevation models (DEMs) to detect and quantify natural karst depressions along the Sã o Francisco River near Barreiras city, northeast Brazil. The study area is a karst landscape characterized by karst depressions (dolines), closed depressions in limestone, many of which contain standing water connected with the ground-water table. The base of dolines is typically sealed with an impermeable clay layer covered by standing water or herbaceous vegetation. We identify dolines by combining the extraction of sink depth from DEMs, morphometric analysis using GIS, and visual interpretation. Our methodology is a semi-automatic approach involving several steps: (a) DEM acquisition; (b) sink-depth calculation using the difference between the raw DEM and the corresponding DEM with sinks filled; and (c) elimination of falsely identified karst OPEN ACCESSRemote Sens. 2014, 6 331 depressions using morphometric attributes. The advantages and limitations of the applied methodology using different DEMs are examined by comparison with a sinkhole map generated from traditional geomorphological investigations based on visual interpretation of the high-resolution remote sensing images and field surveys. The threshold values of the depth, area size and circularity index appropriate for distinguishing dolines were identified from the maximum overall accuracy obtained by comparison with a true doline map. Our results indicate that the best performance of the proposed methodology for meso-scale karst feature detection was using ALOS/PRISM data with a threshold depth > 2 m; areas > 13,125 m 2 and circularity indexes > 0.3 (overall accuracy of 0.53). The overall correct identification of around half of the true dolines suggests the potential to substantially improve doline identification using higher-resolution LiDAR-generated DEMs.

O presente trabalho tem como objetivo quantificar o uso da Terra e suas mudanças no município de Luis Eduardo Magalhães usando dados de sensoriamento remoto. A região teve uma grande expansão da agricultura e do agronegócio desde a década de 1980, devido às condições ambientais favoráveis com terras planas e estação chuvosa bem definida. As principais culturas são soja, algodão, milho e café, mas o solo do Cerrado também produz frutas, feijão e arroz, além de pastagens. O método de detecção de mudança de pós-classificação foi utilizado para determinar as diferenças entre as imagens durante as últimas duas décadas. Esta metodologia requer a comparação de imagens classificadas independentemente, minimizando os problemas de normalização da atmosfera, diferenças de sensor e condições ambientais (fenologia, ciclos precipitação e umidade do solo). Imagens ALOS e Landsat foram utilizadas para elaborar mapas a partir da classificação da cobertura e uso da Terra entre 1987 e 2008. O método utilizado para classificar cada imagem foi a interpretação visual. Durante os últimos 20 anos, os agricultores converteram cerca de 40% das áreas de cerrado em áreas de agropecuária. As mudanças na cobertura e uso da Terra do município de Luis Eduardo Magalhães refletem os impactos das decisões tomadas na política agrícola e econômica.

The current high price of potassium chloride and the dependence of Brazil on imported materials to supply the domestic demand call for studies evaluating the efficiency of alternative sources of nutrients. The aim of this work was to evaluate the effect of silicate rock powder and a manganese mining by-product, and secondary materials originated from these two materials, on soil chemical properties and on brachiaria production. This greenhouse experiment was conducted in pots with 5 kg of soil (Latossolo Vermelho-Amarelo distrófico -Oxisol). The alternative nutrient sources were: verdete, verdete treated with NH 4 OH, phonolite, ultramafic rock, mining waste and the proportion of 75 % of these K fertilizers and 25 % lime. Mixtures containing 25 % of lime were heated at 800 ºC for 1 h. These sources were applied at rates of 0, 150, 300, 450 and 600 kg ha -1 K 2 O, and incubated for 45 days. The mixtures of heated silicate rocks with lime promoted higher increases in soil pH in decreasing order: ultramafic rock>verdete>phonolite>mining waste. Applying the mining waste-lime mixture increased soil exchangeable K, and available P when ultramafic rock was incorporated. When ultramafic rock was applied, the release of Ca 2+ increased significantly. Mining subproduct released the highest amount of Zn 2+ and mn 2+ to the soil. The application of alternative sources of K, with variable chemical composition, altered the nutrient availability and soil chemical properties, improving mainly plant development and K plant uptake, and are important nutrient sources.