Impacts of topographic attributes on Soil Taxonomic Classes and weathering indices in a hilly landscape in Northern Iran

Geochemical weathering indices are widely used in evaluating the stage of soil development. However, their compatibility with Soil Taxonomic Classes has not been studied yet. This study was conducted in a hilly region to illustrate the relations between soil development indices and topographic attributes and Soil Taxonomic Classes. A grid sampling method was carried out with 100 m intervals. Physico-chemical analyses and total elemental analyses were performed on 184 and 56 soil samples respectively. In addition, eight topographic attributes and 12 common soil development indices were determined. Results showed that among the topographic attributes, slope gradient and topographic wetness index (TWI) had the highest correlation with Soil Taxonomic Classes and development indices. Morphological index (r = 0.60) and Feo/Fed ratio (r = 0.52) increased with progress in soil development from Entisols to Alfisols and Mollisols. Despite the significant correlations between most of the geochemical weathering indices and Soil Taxonomic Classes (Vogt index had the highest correlation coefficient (r = − 0.74)), these indices represented lower weathering intensity in more developed soils. These relationships were due to the predominance of more developed soils in low gradient slopes, where the weathering products of upper slopes accumulate and their parent materials are carbonatic.