The roles of parent material and toposequence on geochemical characteristics and pedogenic iron oxides of soils

Abstract

Soil formation is highly associated with topographic position and parent material, both of which play roles in the morphological, mineralogical and weathering processes of soils, particularly on the local level. Landscape topography conducts soil formation through affecting biogeochemical process and regulating soil hydrological process in the surface part of the earth, while parent material has a considerable effect on the types and concentrations of elements found in soil. This study aimed to determine how pedogenic and other factors affect soil classification by identifying the geochemical characteristics of soils classified as vertisols, inceptisols and entisols located on different topographies and possessing different parent material. Following macro-morphological identification of six typical soil pedons, samples were taken from different soil layer and their geochemical, mineralogical and other characteristics were analyzed. These characteristics were also evaluated for possible use in identifying soil maturity stages and periods of late-quaternary soil formation. The pedogenic evolution of soils was also examined using genetic ratios, which combine major oxides and selective dissolution analysis (Fe_o-Fe_d) values into a single metric. All pedons had Si/Al ratios above 2, indicating arid, sub-arid, sub-humid or high precipitation with cold areas. In addition, Fe_d(dithionite extractable iron) values were higher than Fe_o(oxalate extractable iron) and lower Fe_t(total Fe oxides) values, ranging between 0.007 % and 0.031 %. Therefore, the results clearly showed that local soil geochemical, mineralogical and morphological characteristics in the research area were strongly influenced by topographic conditions and parent material either directly or indirectly.