The study of physicochemical and mineralogical properties of soils in a toposequence in South West of Urmia Lake

In order to study the effects of topography on morphological, physicochemical and mineralogical properties of soils, a toposequence composed of three land types (hills, plateau and piedmont plain) in Heydarabad region in the south west of Urmia Lake between Urmia and Mohammadyar cities was investigated. Considering the variations in slope and elevation, type two soil profiles were dug, described and classified in each land and soil samples were taken from genetic horizons and their physicochemical and mineralogical properties were determined using standard methods. According to the results, the depth of soil, solum thickness, the depth and thickness of calcic horizons, the values of clay content, organic carbon, cation exchange capacity, electrical conductivity and calcium carbonate equivalent of soils were increased with decreasing in the slope and elevation of region to the downward of toposequence. Additionally, in the lower part of toposequence (piedmont plain land type), vertical translocation of clay has been lead to the formation of argillic horizons. According to clay mineralogical investigations, illite, smectite, chlorite, kaolinite, vermiculite and palygorskite were the major clay minerals in these soils. Clay mineralogical investigations revealed that in the higher parts of toposequence (soil profiles 1 and 2, hills land type) illite and chlorite were the common clay minerals. Gradually, with decrease in slope, the content of smectite in soils were increased and reached to the highest value and become the dominant clay mineral in the lower part of toposequence (soil profiles 5 and 6, piedmont plain land type). In soil profile 4 (plateau land type), in addition with smectite and illite, palygorskite is present as one of common clay minerals. Variations of topography from hills to plateau and piedmont plain have been effected the value of runoff, the amount of penetrating water and vertical translocation of salts and so affected the development and evolution of soils. Finally, differences in physicochemical and mineralogical properties of soils have been lead to the differentiation of soils along toposequence and their classification in three orders Entisoils, Inceptisols and Alfisols.