Pedogênese de horizontes com caráter coeso em duas topossequências nos Tabuleiros Costeiros do Ceará

Abstract

The Coastal Tablelands are a geomorphological unit associated with sediments of Barreiras Formation and feature great interest to farm. However, some soils of this region have subsurface horizons with cohesive character, which can cause physical impediments to the development of the root system and the dynamics of water. The genesis of the cohesive character has not yet been fully elucidated, but it is known that occurs naturally. However, some studies have linked the genesis of these horizons to several factors such as particle size of the soil, clay translocation processes and the action of organic and inorganic cementing agents. Thus, this study was conducted in order to obtain greater insight into the characteristics and the genesis of soils with this character. Therefore, soils were studied presenting horizons with cohesive character, seeking to identify and characterize processes that govern the genesis horizons with cohesive character in soils of Coastal Tablelands of Ceará. The study was conducted in two areas of the Coastal Plains of the state of Ceará (Pacajus and Trairi), where soils are arranged in topossequence and present cohesive character. The samples were subjected to physical fractionation of the sand fraction and morphoscopic analysis. Sequential extraction was carried out on Si surface and subsurface horizons, as well as chemical fractionation of humic substances. The results show that the two areas of study have different processes associated with the genesis of cohesive. In Pacajus soils showed moderate degree of selection, however the high concentration of clay subsurface influences the density of these soils. The cohesive soils of Trairi have a poor degree of selection, which facilitates the adjustment of these particles and the action of low crystalline compounds as cementing agent.