Geochemical Processes Leading to Variation of Soil Development on Calcareous Toposequence in Semiarid Fields

Abstract This study was carried out in soils formed in different physiographic units (summit(PI), shoulder(PII), backslope(PIII), footslope(PIV)) on the limestone parent material under the same climatic conditions.The study was assessed clay mineralogy, weathering indices, mass loss/gain states, and physicochemical properties of different profiles with limestone parent material. It is concluded that smectite clay mineral is dominant in the footslope unit (PIV), with differences in clay mineralogies due to physiographic change. The highest aggregate stability (63.74%) was determined in the in situ physiographic summit unit. The soil's field capacity and wilting point contents showed statistically significant changes with the increase in smectite minerals and clay in the PIV profile on the footslope unit (p <0.01). A positive (0.506; p <0.05) correlation was found between the variability in physiographic units (from Summit to footslope) and the available water content (AWC). Bulk density and porosity characteristics varied depending on the particle size distribution and the type of land use. The soils formed in shoulder and backslope units, which are in the Entisol soil class, are classified as "not decomposed" according to the Chemical Alteration Index (CIA), Chemical Weathering Index (CIW), and Plagioclase Alteration Index (PIA) values. In the Inceptisol and Vertisol ordo, it was determined that the basic cations were leached in the PI and PIV profiles in the summit and footslope units, and the separation was more advanced. The highest losses from the soil were obtained from the backslope, while the gains were obtained from the footslope physiographic unit. As a result of this study, it has been revealed that soil formation in the summit and bottom lands (footslope) is more effective than other physiographic units, and physicochemical properties are affected by these processes.