Fig. 4. Cumulative soil CO₂–C emissions from exposed subsoil planted to three cropping systems during the growing seasons of 2003 and 2004: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. The crop was corn in 2003 and soybean in 2004 in the corn–soybean rotation. Means with the same letter within each year are not different at P 0.05.