Geochemical and Mineralogical Processes Leading to Variation of Soil Characteristics on Calcareous Toposequence in Semiarid Ecosystem Condition

Abstract

Soils are under the influence of their formation processes at varying rates. Determining the variability and characteristics of soils due to the formation processes' effects is vital for sustainable soil management. This study aimed to investigate soils formed on limestone and on different physiographic units (summit, shoulder, backslope and footslope) under semiarid climatic condition. That is why, the present study assessed clay mineralogy, weathering indices, mass loss/gain states, and physic-chemical properties of different profiles. It is concluded that smectite clay mineral is dominant in the profile IV located on footslope position with differences in clay mineralogy due to physiographical change. The summit physiographic unit includes the highest aggregate stability (63.74%). The soil's field capacity and wilting point contents showed statistically significant variation with the increase in smectite clay minerals in the PIV profile on the footslope unit (p < 0.01). In addition, a positive (0.506; p < 0.05) directional relationship was found between the variability in physiographic units (from summit to footslope) and the available water content (AWC). In addition, bulk density and porosity characteristics varied depending on the particle size distribution and land use type. The soils formed on shoulder and backslope units classified as Entisol soil order are described as "not decomposed" according to the Chemical Alteration Index (CIA), Chemical Weathering Index (CIW), and Plagioclase Alteration Index (PIA) values. On the other hand, in the Inceptisol and Vertisol soils, it was determined leaching process for basic cations in the PI and PIV profiles located on the summit and footslope. As for mass balance system, the highest losses from the soil formed on the backslope whereas, the PI and PIV formed on the footslope position gains. As a result of this study, it has been revealed that soil formation process in the summit and footslope is more effective than in other physiographic units. Therefore, physico-chemical properties are mainly affected by these processes.