Effective employment of conservation tillage (CT) and crop management practices to increase C sequestration will require an understanding of quantitative relationships between crop residue inputs under different rotations and potential changes in soil organic carbon (SOC) content. A field study was initiated in the late 1990's to compare cropping system effects (centered on surface tillage) on SOC levels and to establish relationships between crop residue inputs with changes in SOC contents. A 7-ha field that contained well-drained upland soils and a depressional area composed of several poorly drained soils were divided into two 3.5-ha fields. Between 1998 and 2005, both fields were under a 1 yr rotation of winter wheat (Triticum sp.) and soybean (Glycine max, L.), which was followed by 3 yrs of a corn (Zea Maze L.), and cotton (Gossypium hirsutum L.) annual rotation plus 1 additional yr of cotton. One field was tilled using disk tillage (DT) and the other using CT. Annual soil samples at 0 to 3-cm and 3- to 15-cm depths and crop residue samples were collected from both fields. Total residue OC mass input for the fields under CT and DT sides was 20.7 and 17.7 Mg/ha, respectively. In spite of this high total, only 4.3% of the OC residue mass input under CT entered the SOC pool. When averaged across each field, significant differences in SOC content in the soil under CT first occurred after 6 yrs of management. A significant change in SOC content (+0.9 Mg/ha) only occurred at the 0 to 3-cm soil depth. Results from this study show that only a small portion of the organic carbon from crop residue inputs will be incorporated into the SOC pool; however, over the long term, this can result in a significant SOC increase in the top few cm of soil.