Increased atmospheric carbon dioxide (CO2) could have negative impacts on the environment. Producing and creating bioenergy in the form of biofuels and electricity from crops is a practical approach to reducing CO2 buildup by displacing fossil fuels and sequestering carbon (C). The use of switchgrass (Panicum virgatum L.) as an energy crop can contribute to clean burning fuels, but no studies addressing soil C sequestration as influenced by use of switchgrass as an energy crop have been conducted. Our objective was to determine the effect of different cultural practices on soil C sequestration under switchgrass. Field experiments were designed to provide differences in row spacing, nitrogen (N) rate, switchgrass cultivar, and harvest frequency on a variety of soils. Our results showed that N application, row spacing, harvest frequency, and switchgrass cultivar did not change soil organic C in the short-term (2-3 yr) after switchgrass establishment. However, after 10 yr under switchgrass soil organic C was 45 and 28% higher at depths of 0-15 and 15-30 cm, respectively, compared with fallowed soil in an adjacent area. It appears that several years of switchgrass culture will be required to realize a soil C sequestration benefit. (C) 2000 Elsevier Science Ltd. All rights reserved.