In the Agreste region of Pernambuco state, Planosols are economically highly important, due to the degree of occupation, as well as the heavy use, mainly for agricultural activities. Aspects such as duality or reworking of parent material, which characterize the processes involved in the formation of the marked textural differences and of Na and salt concentrations, are important points to be clarified. This study aimed to evaluate the pedogenetic process of the Planosols in the region Agreste, state of Pernambuco, based on physical, chemical, mineralogical, macromorphological, and especially micromorphological data. Three soil profiles with marked textural contrast were studied, in trenches opened along a soil toposequence. Physical, chemical, mineralogical, and macro and micromorphological analyses were performed. The soils were found to be autochthonous and the sharp textural contrasts due to argilic Bt horizons seem to be mainly the result of a combination of processes and not simply Elution-illuviation. The processes include the weathering of biotite, forming in situ clay fraction, and losses due to lateral movement by mechanical drag or dissolution. The exact combinations of these processes and Na accumulation were strongly related to the soil position in the landscape.
pedogenesis; Bt planic horizon; micromorphology; biotite weathering
