Eco-physiology of three perennial bioenergy systems
Abstract
Comparative data on biomass accumulation/partitioning and macronutrient cycling within potential perennial bioenergy cropping systems grown in the US Midwest are sparse. My objective was to compare aboveground biomass yields, nutrient cycling, and potential ecosystem impacts of systems considered for commercial production to inform which, if any, are capable of meeting required targets outlined in government mandates. Results from this study assessing Miscanthus × giganteus , switchgrass (Panicum virgatum, 'Shawnee'), and an unmamaged big bluestem- (Andropogon girardii) dominated prairie indicate that Miscanthus annually accumulated more aboveground biomass, and thus attained higher ethanol production estimates (16 to 38 Mg ha-1; 5006 ± 344 L ha-1) than switchgrass (9 to 13 Mg ha-1; 2430 ± 176 L ha -1) and prairie (3 to 6 Mg ha-1; 1031 ± 170 L ha-1). This high biomass production resulted in more nitrogen (N), phosphorus (P), and potassium (K) accumulation in Miscanthus than in the other crops. Miscanthus increased rhizome mass three-fold during this three-year study, resulting in the highest rhizome N, P, and K accumulation of the candidate systems. This high amount of biomass allocated belowground by Miscanthus was associated with a consistent ability to remobilize nutrients (38% N, 76% P, 52% K) from shoots to rhizomes/roots/stembases at the end of the growing season. The consistency of annual nutrient remobilization in switchgrass and prairie was less pronounced. Carbon (C) concentrations were similar among systems and tissues (mean: 443 mg C g-1 dry matter), identifying total belowground biomass accumulation as the main factor contributing to system soil C sequestration potential. Analyses of tissue composition to assess system persistence and regrowth potential suggest Miscanthus relies primarily on organic reserve accumulation in rhizomes and exhibits more dramatic fluctuations in belowground organic reserve accumulation than the other systems. Results from this study identify Miscanthus as having high potential of meeting both energy density and environmental guidelines outlined in government mandates. Data from this research further our understanding of these novel cropping systems, and when used to parameterize large-scale models, can inform government policy on renewable energy strategies.
Degree
Ph.D.
Advisors
Volenec, Purdue University.
Subject Area
Agronomy
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