Organic carbon (OC) fractions play an important role in soil and many ecosystem processes. This study focuses on changing of OC in different fractions in a soil treated with different levels of zeolite and plant residue that incubated for 90 days. The results showed that the amounts of light fraction (LF) and heavy fraction (HF) increased with increasing the percentage of zeolite and plant residues in the soil. The highest amounts of LF (22.7 g LF. Kg-1Soil) and HF (26.7 g. Kg-1Soil) were found when 30% zeolite, 5% wheat and alfalfa straws was added to the soil respectively. Accordingly, wheat straw and alfalfa straw were effective for increasing the LF and HF respectively. However they declined with decreasing the OC from the 1st day of experiment until the 90th day of experiment. Soluble OC in hot (2.80 g. Kg-1Soil) and cool (2.25 g. Kg-1Soil) water fractions increased with the addition of 30% zeolite and 5% plant residues particularly alfalfa straw in comparison with control. Although they increased after 30 days of starting incubation but, then they decreased in the continuation of the experiment. In fact, OC contents in density and soluble fractions increased with application and addition of 30% zeolite and 5% plant residues into the soil; however they decreased after 30 days of incubation with decreasing the OC. The findings of this research revealed the application of zeolite and plant residues improved carbon pools in density and soluble fractions and carbon sequestration increase by increasing the OC contents in soil.
