The Archipelago of Fernando de Noronha (FN), Brazil, has poorly developed soils of the Cambisol, Vertisol, and Leptosol classes (WRB-FAO), with particular characteristics related to parent material of volcanic origin, a tropical climate with oceanic influence, and rolling to strongly rolling relief. The Vertisols of FN are formed from basic rocks, volcanic tuffs, and alluvial sediments. They are associated with depressed surfaces that have impeded drainage from the central highlands and coastal plains. In view of the need for environmental conservation, agricultural or geotechnical use, and the particular characteristics of this island environment, the Vertisols of FN require better understanding of their properties. The aim of this study is therefore to characterize the morphological, physical, chemical, and mineralogical properties of native Vertisols from the main island of Fernando de Noronha. Three profiles of Vertisols derived from different parent materials, drainage classes, and soil salinity and sodicity levels were described and sampled for soil characterization. The soils studied were classified, according to the WRB-FAO, as Haplic Vertisol (P01), Salic Vertisol (P02), and Sodic Vertisol (P03). The Vertisols of FN exhibit typical features such as clayey to very clayey texture, slickensides, and horizontal and vertical cracking when dried. They are imperfectly to poorly drained and are temporarily flooded during the rainy season. They exhibit high base saturation and high to very high levels of available phosphorus irregularly distributed among the soil profiles, mostly in inorganic forms. However, there are problems of salt accumulation, which restricts their geotechnical or agricultural use. The main minerals in the clay fraction of the Vertisols of FN are the smectite group, followed by kaolinite and/or halloysite. The silt fraction consists of hematite, goethite, magnetite/maghemite, ilmenite, mica, and feldspar minerals and by minerals uncommon in Brazilian soils, such as crandallite and hollandite.
Brazilian oceanic islands; pedology; soil mineralogy
