Conservation tillage (CT) and cover cropping are sustainable agricultural practices that may provide solutions for California's declining soil, air and water quality. These practices can increase soil organic matter, reduce dust production conserve water and increase soil C. We looked at total C as well as followed the decomposition of 13C labeled cotton residue through within three physical fractions: free POM, aggregate-protected POM, and mineral associated organic matter. With the decrease in soil disturbance under CT and increased C inputs with cover cropping, we expect total C and aggregate-protected POM to increase in both the CT and the cover crop treatments over the long term. Initial inspection of soil C numbers suggest that cover cropping increases total soil C in both CT and standard tillage on the order of 4500 kg C/ha in CT and 3800 kg C/ha in standard tillage in the top 30 cm over a 5-year period. In the CT treatments, the increase occurred in the surface 15 cm, while in the standard tillage treatments, it was distributed throughout the top 30 cm. In the treatments without cover crops, there was no change in soil C in the 0-30 cm depth. In dry hot irrigated systems, cover cropping was more important for soil C accumulation than tillage practice.