Cropping systems effects on improving soil carbon stocks of exposed subsoil

Removal of topsoil from glacial-till-derived sods exposes unproductive subsoil that is low in soil organic carbon (SOC) and nutrient availability The overall objective of this study was to evaluate the long-term impacts of a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation and a managed switchgrass (Panicum virgatum L.) system in improving soil C stocks of exposed subsoil. The experimental layout of this study was a randomized complete block design with four replications. Field soil CO2, emissions, potential crop residue total C input, microbial biomass C, soil C fractions, soil incubation CO2 emission, and soil bulk density were measured from switchgrass burned annually (SA), switchgrass burned every 5 yr (S5), and corn-soybean rotation (CS) cropping systems in 2003 and 2004. During both years of the study, the SA cropping system had the greatest cumulative soil CO2-C emissions, followed by the S5 and CS cropping systems, respectively. The S5 cropping system produced 3.47 and 2.33 Mg ha(-1) more aboveground biomass than soybean and corn, respectively. Switchgrass had 14 Mg ha(-1) greater root biomass than corn or soybean. As a result, potential C input from the S5 switchgrass treatment was 6.08 and 6.71 Mg ha(-1) greater than corn and soybean, respectively. Microbial biomass C was 200% greater in the switchgrass cropping systems (S5 and SA) than in the corn-soybean rotation. The switchgrass system is an effective strategy for improving-, exposed subsoil C fractions and providing greater potential C input through a more extensive root system than the corn-soybean rotation.