Digital morphometrics and genesis of soils with buried horizons and lithological discontinuities in southeastern Brazil

Abstract

Soil morphometrics aims to measure attributes observed in soil profiles. The use of digital technologies in the morphological study of soil profiles has yet to be further explored by the scientific community. Particularly, soils with buried horizons, which are common in lowlands and floodplains throughout the world, have never been examined using digital morphometrics. This study aimed to examine the morphology and genesis of three soil profiles with buried horizons in Brazil using digital soil morphometrics combined with wet-chemistry and mineralogical analyses (including X-ray diffraction – XRD). Digital analyses used three proximal sensors – portable X-ray fluorescence spectrometry (pXRF), visible near-infrared (Vis-NIR) and mid-infrared (MIR) diffuse reflectance spectrometry. The soils had buried horizons and were classified as Typic Udifolists (TU), Typic Dystrustepts (TD) and Typic Endoaquents (TE). Each soil profile was sampled in a 15 × 15 cm grid, with 40 samples per profile. All sensors identified the buried soil horizons. Vis-NIR and MIR identified the presence of several key minerals and variations in soil organic matter (SOM) that were not observed in the whole soil pits. PXRF captured discontinuities in the parent material, not only between deposited and buried horizons, but also within horizons. The deposited material above TU and TE was derived from neighboring Fe-rich Oxisols and Ultisols, as shown by high Fe content and absorption features of Fe oxides. Sensor analyses were quick and environmentally friendly. Proximal sensor data enhanced morphological assessment of soil profiles, and provided insights otherwise very difficult or even impossible with only traditional and visual methods.