Fig. 5. Microbial biomass C content in the 0- to 15-cm depth of exposed subsoil planted to three cropping systems: 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.