Cropping Systems Effects on Improving Soil Carbon Stocks of Exposed Subsoil

Abstract

Removal of topsoil from glacial‐till‐derived soils 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 0reater 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.