Soil Organic Carbon, Aggregation, and Microbial Community Structure in Annual and Perennial Biofuel Crops

CORE IDEAS: Removal of corn and sorghum residues did not affect soil carbon under no‐tillage. Soil carbon (0–15 cm) increased in 10‐yr stands of switchgrass and miscanthus. Soil carbon increased with root biomass, fungi abundance, and soil aggregate size. Perennial crops improved soil health while providing feedstock for biofuels. The substitution of cellulosic biofuel in place of conventional fuels could reduce greenhouse gas (GHG) emissions from transportation. However, changes in soil organic carbon (SOC) and soil health during biofuel crop production could have a major impact on the GHG balance of biofuels. We assessed temporal changes (10 yr) in SOC stocks to a 90 cm depth in Cumulic Hapludolls from central Kansas under perennial and annual cropping systems. The perennial crops were miscanthus (Miscanthus sacchariflorus) and switchgrass (Panicum virgatum L.). The annual cropping systems were continuous corn (Zea mays L.), and corn, dual purpose–grain sorghum (Sorghum bicolor (L.) Moench), sweet sorghum, and photoperiod‐sensitive sorghum (PS) in rotation with soybean [Glycine max (L.) Merr.]. All standing aboveground biomass was removed at harvest of corn, sorghum, and perennial crops. Stocks of SOC increased in the 0–15 cm depth under switchgrass and miscanthus by 0.8 and 1.3 Mg C ha⁻¹ yr⁻¹, respectively. The SOC stocks did not change at the other depths or at any depth in the annual cropping systems nor throughout the soil profile under any crops. Root biomass measured in the seventh year of the study was 3.7 to 7.8 times greater in perennials than in annual crops. Increases on SOC were correlated with greater root biomass, abundance of arbuscular mycorrhizae and saprophytic fungi, and soil aggregate diameter. These results demonstrate the potential for perennial biofuel crops to enhance C sequestration and improve soil quality while providing feedstock for production of cellulosic biofuel.