Catena of Ultisols from southeastern Brazil: assessing variation within and among pedons

Abstract

Despite having the second largest territorial extension in Brazil (2,281,135 km2, constituting 26.79% of the country's area), the variability of Ultisols' attributes has not received proportional attention compared to Oxisols (31.61% of the country's area). A very representative catena of Ultisols derived from gneiss in Southeastern Brazil was analyzed to assess the variation of their physical, chemical, magnetic and mineralogical attributes within and among pedons. For that, a complete series of traditional and novel techniques were employed: conventional morphological, physical and chemical analyses, digital morphometrics via X-ray fluorescence spectrometry, magnetic susceptibility analyses and X-ray diffraction. Analyses highlighted how low natural soil fertility varied within and in between soil profiles. The differential concentration of residual elements Zr and Ti, the magnetic susceptibility values and mineralogy data indicated that the Inceptic Hapludult, situated at the inferior third of the catena, received sediments from upslope Ultisol areas. Kaolinite largely predominated in the clay fraction. Digital soil morphometrics allowed for a more objective and detailed assessment of the variation of Ultisols' attributes in the studied catena. It confirmed the field identification of the B/C horizon in the Typic Rhodudult and indicated variation of soil parent material. Enhancing soil variability assessment by combining conventional and digital methods can enrich the knowledge about landscape evolution and help devise better management practices.