Measured soil organic carbon was compared to data from a cropping simulation model, Cycles, to predict soil organic carbon. Management (MGT) and no-till (NT) had the highest carbon in the top 5-cm, but occasional-tillage (OT) had the highest carbon in the 5-10 cm and 10-20 cm layers. These results indicate that carbon inputs from crop residues and manure may need to be incorporated occasionally in order to increase the amount of C stored in soil.