Establishing bioenergy plantations is important to developing alternatives to fossil fuel.  Yet, research information about the impact of growing bioenergy crops on soil organic carbon (SOC) concentration and pool and their depth distribution is scanty and fragmented.  In this regard, long-term agroecological sites are a valuable tool in assessing management-induced changes in SOC concentration and pool.  Therefore, the principal objective of this study was to assess SOC and nitrogen (N) concentrations and pools under long-term (> 12 years) switchgrass (Panicum virgatum L) plots for five soils in the upper Southeast, U.S.  Five soil series selected were Cecil in North Carolina, Chatter and Davidson in Virginia, Dormont in West Virginia and Etowah in Tennessee.  Soil cores were collected to 50-cm depth and subdivided in 10-cm depth increments for measuring field bulk density (r_b), moisture content, SOC, and total N concentrations.  Results showed differences in r_b, moisture content, C and N concentrations and pool among soil depths for different soil types and management practices.  Forestland had a higher SOC pool to 50-cm depth in all soils.  Soil under switchgrass contained more SOC pool than that under pasture at Cecil (44.8 vs. 39.2 Mg ha^-1) site only.   In Davison, soil under switchgrass contained 64.5 Mg C ha^-1 compared with 30.2 Mg C ha^-1 under cropland.  A strong linear relationship occurred between C and N in pools for each soil type and land use.  Such empirical relationships, however, were soil and land use specific.