Fig. 7. Cumulative soil CO₂–C emissions from exposed subsoil planted to three cropping systems after a 77-d laboratory incubation study: SA is switchgrass burned annually, S5 is switchgrass burned every 5 yr, and CS is corn–soybean rotation. The crop was soybean for the corn–soybean rotation when the field was sampled. Means with the same letter are not different at P 0.05.