Soil-landscape relationship in sandstone-gneiss topolithosequence in Amazonas, Brazil

Abstract. Soil position in the landscape reveals its history of formation and genesis. Therefore, the landscape is the combination of features of the surface of the earth with subsurface components (parent material), while the soil is a three-dimensional, dynamic natural body inserted in the landscape. This research aimed to study the soil-landscape relationship in a sandstone-gneiss topolithosequence in Amazonas, Brazil. The study was carried out along a 9.253-meter transect from the top downwards the softer slope. Soil profiles were selected in five landscape compartments (top, upper third, lower third, transport foothill, and deposition foothill). Morphological, mineralogical, physical, chemical, and ray diffraction characterizations were performed. Soils had different morphological, physical, chemical, and mineralogical attributes due to the variations of the geological substrate and landscape position. The mineralogy of the clay fraction is composed of kaolinite, goethite, hematite, and gibbsite, with goethite being the predominant iron oxide. A sand fraction dominance was observed in relation to the other fractions in all the profiles, being related to the alluvial nature of the parent material, with the highest values occurring in the lower third. The separation of the landscape into geomorphic surfaces and identification of the parent material were effective for understanding the variation of soil attributes along the landscape.