The objective of this study was to evaluate the physical, chemical, mineralogical and micromorphological characteristics of cohesive red, yellow and grayish soils in a toposequence of the Coastal Tablelands region in southern Bahia and northern Espirito Santo states. It was also sought to understand the mechanisms promoting their cohesion and fragipan formation. Therefore, the routine physical analyses, determination of the coarse clay/fine clay ratio, specific surface by BET-N2 and water vapor adsorption, magnetic susceptibility, scanning-electron microscopy analyses and the micromorphology of thin plates were carried out. Physical and micromorphological analyses indicated that the high content of very fine clays, especially those smaller than 0.2 µm, translocated among horizons or within a same horizon as dispersed clay, were responsible for the genesis of the cohesive horizons. The higher cohesion observed in the Yellow Argisol (Ultisol) found in a drier climate, compared to those in a more humid climate could be due to the less clayey granulometry and a larger amount of clay illuviation features.
Barreiras Group; cohesion; fragipan
