Abstract
In Brazil, the state of Rio Grande do Norte has an important coastal zone and coastal Tableland areas along the Barreiras Formation, but there are few studies to locate and characterize soils with cohesive character. Therefore, this work was carried out to characterize pedons in the western and eastern mesoregions of the state, located in the Barreiras Formation and with different climatic conditions. The profile description and sample collection were carried out in March and April 2016. The characteristics of the profile identified were the sequence of horizons and their depth, soil color, texture, structure, consistency, and transition between horizons. The physical analyzes were of soil density and texture. The chemical analyzes consisted of: pH in water and in KCl, contents of available P, Na+, K+, Ca2+, Mg2+, potential acidity, and total organic carbon. Indices obtained were: base sum, effective cation exchange capacity, cation exchange capacity at pH 7.0, base saturation, exchangeable aluminum saturation, and exchangeable sodium percentage. The profiles were classified up to the fourth categorical level. The mineralogical assembly was identified in the clay fraction of the diagnostic horizons. The identification of the minerals was performed by X-ray diffraction. The pedons of the two regions presented distinct characteristics and pedogenesis, occurring laterization in the pedons of the western mesoregion and podzolization in the pedons of the eastern mesoregion, both without presence of cohesive character as a diagnostic attribute.
Highlights
The Barreiras Formation occupies the coastal zone and part of the sub-coastal zone of almost the entire Eastern and Northern Coast of Brazil
The soil profiles located in the region of the Barreiras Formation presented an intense distinction in relation to its edaphic characteristics, mainly morphological variations, when observed from the West region to the East region of the State of Rio Grande do Norte (Figure 2)
They are developed from the same lithogenetic formation, which is a set of sedimentary rocks that form the coast of the state of Rio Grande do Norte, there is a significant heterogeneity in relation to the pedogenesis
Summary
The sediments present low levels of Fe and are essentially kaolinitic, with poorly selected quartz skeleton (Melo, Schaefer, Singh, Novais, & Fontes, 2002) This favors the compaction of the soils of these origins, with the development of blocky macrostructure, and can give rise to high density soils, with greater amount of micropores and lower permeability, due to the arrangement of the clay fraction (Ferreira, Fernandes, & Curi, 1999a). Along the Barreiras Formation, the soils formed in the Coastal Tablelands are the most representative in terms of agricultural land use These soils have subsurface mineral horizons, which have a friable consistency when wet, but when dry, they present a hard, very hard or extremely hard consistency, exhibiting a strong cohesion (Jacomine, 1996; Ribeiro, 2001a). Another process would be the obstruction of soil micropores by the migration of fine materials to the lower parts of the profile (Giarola & Silva, 2002), as well as the face-to-face adjustment of the clays, resulting in increased soil density (Ferreira, Fernandes, & Curi, 1999b)
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