The objective of this research was to isolate biologically meaningful and measurable soil organic matter (SOM) fractions related to the organic carbon (C) pools described in the Century SOM model. This was achieved by measuring the changes of isolated C fractions during a six-month incubation study of three different soils, varying in clay content, amended with 14C-soybean residues using physical and chemical fractionation techniques. Additionally, we studied the effect of clay content and residue placement on the fate of the added residue C. The SOM fractions most responsive to the added C were microbial biomass C and the light fraction. The humic acid fraction showed a tendency to accumulate during the incubation, but a much longer incubation is required to obtain an accurate measure of its dynamics. Adoption of no-tillage practices combined with surface residue placement may promote C sequestration in surface soil layers.