Threshold Dynamics in Soil Carbon Storage for Bioenergy Crops

Friday, 19 December 2014
Dongkook Woo1, Juan Quijano1, Praveen Kumar1, Sayo Chaoka2 and Carl Bernacchi1, (1)University of Illinois at Urbana Champaign, Urbana, IL, United States, (2)Wood Rodgers Corporate, Sacramento, CA, United States
Due to increasing demands for bioenergy, a considerable amount of land in the Midwestern United States could be devoted to the cultivation of second-generation bioenergy crops, such as switchgrass and miscanthus. In this study, we attempt to explore and analyze how different amounts of above-ground biomass returned to the soil at harvest affect the below-ground dynamics of carbon and nitrogen as a comparative study between miscanthus, swichgrass, and corn-corn-soybean rotation. The simulation results show that there is a threshold effect in the amount of above-ground litter input in the soil after harvest that will reach a critical organic matter C:N ratio in the soil, triggering a reduction of the soil microbial population, with significant consequences in other microbe-related processes such as decomposition and mineralization. These thresholds are approximately 25% and 15% of above-ground biomass for switchgrass and miscanthus, respectively. However, we do not observe such threshold effects for corn-corn-soybean rotation. These results suggest that values above these thresholds could result in a significant reduction of decomposition and mineralization, which in turn would enhance the sequestration of atmospheric carbon dioxide in the topsoil and reduce inorganic nitrogen losses when compared with a corn-corn-soybean rotation.