Soil–landscape relationship in a sandstone-gneiss topolithosequence in the State of Amazonas, Brazil

Abstract

The soil position in the landscape reveals its formation history. Landscapes combine surface features and subsurface components (parent material) of the earth, at which the soil inserts as a three-dimensional and dynamic natural body. The present research aimed to study the soil–landscape relationship in a sandstone-gneiss topolithosequence and the factors determining soil diversification in the State of Amazonas, Brazil. The study extended along a transect of 9253 m, covering the distance between the first and the last profile, for a total of five profiles opened. Profile selection considered landscape topography, from the highest to the lowest relief of the terrain. Soil profiles characterization and classification were based on morphological, chemical, and physical properties and the mineralogy of the clay fraction by X-ray diffraction (XRD). Lithological contrasts and landscape variations determined the different soil types along the topolithosequence. Morphological, physical, chemical, and mineralogical attributes also varied along the landscape. The relief and the parent material, sandstone-gneiss, were the main factors influencing the pedogenesis. Goethite (5–40 g kg–1) was the predominant Fe oxide in all the soils, reflecting the low total iron content (Fet ≤ 68 g kg–1) of the soils and parent materials. The predominance of the sand fraction in all the studied profiles reflected the alluvial nature of the parent material, with the highest values (total sand > 800 g kg–1) occurring in the convex creep slope. Knowing the geomorphic surfaces and the parent material was effective for understanding the variation of the soil attributes along the landscape.