Studying of the Formation and Development of Soils in a Toposequence in Chelgerd Region, Chaharmahal-va- Bakhtiari Province

The optimum and sustainable use of soil is possible only with correct and complete understanding of its properties. The objectives of the this study were to enhance understanding of soils available in an area located on 35 km of Chelgerd region in Chaharmahal –va- Bakhtiari province through the study of the Soil morphological, physico-chemical, mineralogical and micromorphological characteristics to check the formation and classification of these soils according to USDA Soil Taxonomy (2014) and WRB (2014) systems.
Mean annual rainfall and soil temperature of the selected location are 1389.6 mm and 9.5 ℃ respectively and Soil temperature and moisture regimes of this region are mesic and xeric, respectively. Eight pedons located on one transect along slope direction were excavated and sampled. Routine physico-chemical analysis such as soil reaction, texture, COLE content, electrical conductivity, calcium carbonate equivalent, cation exchange capacity, organic carbon and clay mineralogy and micromorphology investigations were performed on selected soil samples. Then, based on description card of each profile and laboratory results, soils were classified to phamily level and to second level based on Taxonomy and WRB systems, respectively.
the results showed that the category of the soils of the area according Taxonomy system, are Inceptisols and Vertisols, while in WRB system, named Calcisols, Cambisols and Vertisols. The results showed that, because of higher organic matter content and finer texture of soils of lower slope positions, cation exchange capacity was maximum in this position. The results also revealed that, with increasing soil depth, organic carbon content and cation exchange capacity decreased, whereas clay and lime content had a reverse trend and increased with increasing the soil depth. Coefficient of linear extensibility (COLE) values as well as clay content increased from back slope to foot slope and with increasing soil depth. They are constituted mainly by smectites associated to some amount of illite, chlorite, kaolinite, quartz and illite- smectite as mixed minerals. According to this results, the origin of the clay minerals in different slope positions are mostly inheritance from parent material. Study of thin section revealed the presence of clay coating in the Bt and Btk horizons, that, this clay coatings in the soil are evidence of transmission clay from upper horizons to lower horizons as a result of water penetration. Also, calcite accumulation with various forms such as calcite coating, calcite infilling and calcite needle and calcite nodule in the Bk and Btk were observed, which, confirms the secondary nature of lime and causing calcitic crystalitic b-fabric. Also, the cause is the accumulation of calcite needle in the top of the slope due to highlands area, presence of enough moisture in the soil, the low salinity of soil and presence of biodegradable organic matter.
the result of this study showed the role of topography on variability of soil properties and soil classification in the studied area.