Journal of Rangeland

  The purpose of this research was to investigate the effects of different land uses on organic carbon distribution in soil size fractions. The sites with 18 years cultivated by Atriplex canescens with high, moderate and none (exclosure) grazing intensities were selected in Shahryar. The sites with 3 years after the cultivation of Atriplex canescens , barely field and control (natural non cultivated lands) were the other studied treatments. A systematic random sampling method was used to collect the soil samples from 0-10, 10-30 and 30-100 cm depths of soil surface with 3 replications. Soil samples were divided to five size fractions using different Sieves, and the carbon content of each fraction was then measured. Results showed that soil organic carbon contents were increased by reduction in fraction size in the all treatments. The highest amount of carbon contents were observed in F₄ and F₅ fractions. The carbon contents of fractions of á 250 µ were more than average soil carbon content, and in the fractions of ñ 250 µ were less than soil average carbon content. Although the carbon contents of the studied treatments were different, but the ratio of fractions carbon content to total soil carbon content in the fractions did not varied significantly. This ratio for 1-2 mm fraction was decreased in the all treatments. This ratio for á 250 µ fractions was increased in the barely field and 18 years cultivated by Atriplex canescens sites with high grazing history. The land management types that increase the carbon accumulation in the fine fractions can be considered as an effective step to sustainable soil carbon sequestration.