Conversion of rangelands to agriculture and other land use changes have historically reduced soil C levels. Soil organic carbon content and its relation to site characteristics are important in evaluating current regional, continental, and global soil C stores and projecting future changes. The object of this study was to compare amount of soil organic carbon in two different land uses including rangelands and dry land farm in semi-arid rangelands of Kurdistan province, Iran. Treatments were selected based on existing only one type of plant cultivation (Triticum sativum) in different slop ranges (2%-40%). Results of organic matter analysis for 12 treatments and 72 soil samples showed that SOC has greatly declined(18.8%) by changing rangelands to dry farming in 9 treatments and in 3 treatments there was not any difference in SOC concentration in rangeland and dry farming land. The highest and decrease rate of SOC (44%) was related to dry land farm with 45% slop while the lowest SOC decrease (0%) was obtained in 2-5 % slop. Regression equation for slop rate and declining of SOC in 12 treatments show that there was a strong relationship between slop percentage and declining in SOC in all of the treatments. In this study we recommend 0-10% slop for converting rangeland to dry land farming because we can’t find inappropriate change in SOC.
