The Objectives of this study were to determine the impact of fertilization, harvest timing, and harvest frequency on changes in soil C and N in switchgrass (Panicum virgatum L.) land enrolled in the Conservation Reserve Program (CRP). Three locations were selected in South Dakota with switchgrass ranging in age from 9 to 25 years. Five N rates (annual spring application of 0, 56, 112, and 224 kg ha-1 and 224 kg ha-1 split between spring and fall), two harvest timing (anthesis and post-killing frost), and two harvest frequency (every year and alternate year) were applied to plots beginning in 2001. Soil profile samples were collected from each plot in the fall of 2000 (Baseline) and the fall of 2004 (Post-treatment). Soil organic carbon (SOC) significantly increased after four years of biomass production management compared to before the practices were put in place. Nitrogen fertilization increased SOC. Post-killing frost and alternate harvests tended to have positive impact on SOC changes, but were not significant. Nitrogen fertilization effects on SOC changes significantly appeared in the 30-60 and 60-90 cm depths. Soil organic C significantly increased in all depths except the 5-10 and 10-20 cm depth, in which there was a significant reduction of SOC. Soil C sequestration rates with N fertilization to 90 cm depth ranged from 1.02 to 4.27 Mg ha-1 yr-1. Total soil nitrogen decreased significantly during the four years of biomass production. Our results indicated that switchgrass managed for biomass production has potential for C sequestration; however, long-term switchgrass biomass production studies are required for a better understanding of changes in soil quality and C sequestration.