Soil Evolution Investigation Using Clay, Iron, Aluminum and Manganese Indices in a Climosequence of Ilam Province

Among the soil forming factors, climate by effect on weathering severity and parent material degradation plays a basic role on soil evolution. In order to investigate the effects of climate on soil physicochemical properties and evolution in Ilam province, two regions from a climosequence were selected. The purpose of this study was to compare soil evolution in a climosequence according to the soil indices of clay, iron, aluminum, manganese, and 5 profiles in each land units of Salehabad and Ilam plains were dug, described and sampled. The results of physicochemical analysis of Salehabad and Ilam soil profiles in two regions were different and significant difference were observed within the all parameters except pH and silt. In addition, electrical conductivity increases in Salehabad soils with ustic moisture regime and hyperthermic temperature regime comparing to Ilam soils with xeric moisture and thermic temperature regimes revealed the climate effect on them and changes in soil orders from Inceptisols in Salehabad to Mollisols in Ilam were related to the changes in moisture and temperature regimes. Soil classification showed that Salehabad soils were placed in Gypsic Haplustepts and Ilam soils were placed in Gypsic Calciusteps, Typic Calcixerolls and Typic Haploxerolls subgrops. Based on obtained results the iron, aluminum and manganese amounts in Ilam soil profiles were higher than those in Salehabad ones and less weathering in Salehabad region were happened by drier climate, lower humidity and higher temperature. Additionally, the results showed that the horizons with gypsum did not have potential to store clay and metal oxides, and the soil evolution according to the distribution and amount of iron, aluminum and manganese offered a better understanding of the soils and their forming conditions and the Ilam soils showed further evolution.