One approach to reducing the concentration of atmospheric carbon dioxide, which is a dominant greenhouse gas, is to develop renewable energy sources from biofuel crops. Switchgrass, (Panicum virgatum L.) as an energy crop, can partly mitigate potential global warming by supplementing fossil fuels and sequestering carbon (C). Although switchgrass grown for energy may impact C sequestration via the input of root biomass, information on the impact of soil management on switchgrass root growth is extremely limited. We determined the influence of row spacing, nitrogen (N) rate, switchgrass cultivar, and soil type on switchgrass root characteristics. Roots were mainly distributed in the surface soil (0-15 cm), and were 90.4 and 68.2% of the total in the intrarow and interrow profile, respectively. Nitrogen application altered root N but not C concentration, implying that any increase in C sequestration by switchgrass roots will be due to increased root biomass rather than increased C concentration. Root weight density generally decreased in the interrow with wider row width, and N application generally did not affect root weight density. Root weight density in the Pacolet soil was higher than in the other four soils, and root density was 4.1 times higher in the Pacolet soil than in the Norfolk soil. Root mass in the Pacolet soil (36,327 kg ha(-1)) was 2.7 times greater than that found in the Norfolk soil (13,204 bg ha(-1)) within 150 cm of the soil surface. Differences in root characteristics were found among cultivars: root weight density with ＇Cave-in-Rock＇ switchgrass was 29.4 and 47.6% higher than ＇Alamo＇ and ＇Kanlow＇, respectively. Variations in switchgrass root biomass production owing to soil type and cultivar suggest that site and cultivar selection will be important determinants of C sequestration by switchgrass roots. A potential benefit of switchgrass is the reduced loss of nutrients associated with non-point pollution, owing to its deep root system that may extend 330 cm below the soil surface. (C) 2000 Elsevier Science Ltd. All rights reserved.