title: Threshold dynamics in soil carbon storage for bioenergy crops.
abstract: Because of 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. The foliar carbon/nitrogen ratio (C/N) in these bioenergy crops at harvest is significantly higher than the ratios in replaced crops, such as corn or soybean. We show that there is a critical soil organic matter C/N ratio, where microbial biomass can be impaired as microorganisms become dependent upon net immobilization. The simulation results show that there is a threshold effect in the amount of aboveground 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 aboveground biomass for switchgrass and miscanthus, respectively. 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 to a corn-corn-soybean rotation.
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Mathews Avenue, Urbana, Illinois 61801-2352, United States.
authors.forename: Dong K
authors.initials: DK
authors.lastname: Woo
authors.forename: Juan C
authors.initials: JC
authors.lastname: Quijano
authors.forename: Praveen
authors.initials: P
authors.lastname: Kumar
authors.forename: Sayo
authors.initials: S
authors.lastname: Chaoka
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Bernacchi
mesh_terms: D000383:Agriculture / Q000379:methods*; D056804:Biofuels; D018533:Biomass; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide; D057965:Carbon Sequestration; D003198:Computer Simulation; D018556:Crops, Agricultural / Q000737:chemistry / Q000378:metabolism; D015146:Midwestern United States; D008962:Models, Theoretical; D009584:Nitrogen / Q000378:metabolism; D058458:Nitrogen Cycle; D006109:Poaceae / Q000737:chemistry* / Q000378:metabolism; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013025:Glycine max / Q000737:chemistry / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism
chemical_list: D056804:Biofuels; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen