Carbon Cycling In Perennial Biofuel Management Systems.

Demand for alternatives to fossil fuels has driven interest in cellulosic biofuel and the desire to mitigate CO₂ emissions has steered researchers towards various methods of sequestering carbon. Perennial grasses hold promise for being both biofuel feedstock and capable of sequestering carbon. In this study, Switchgrass (Panicum virgatum) , Miscanthus (Miscanthus spp.) and Eastern Gammagrass (Tripsacum dactyloides) were evaluated with harvest frequency to determine the best management practices to achieve these dual goals of energy production and sustainability in the Southern Great Plains. The harvest frequency treatments include a single harvest at the end of the growing season (Oct-Nov.) and a split harvest treatment harvested midseason (Aug.) and again at the end of the growing season. Residue samples were collected from a 0.35 m² area within each harvested plot and residue samples were evaluated for moisture and total carbon.  Soil samples were taken in May 2009 and March 2010 to a depth of 80 cm.  Soils were analyzed for organic carbon, bulk density and moisture.  This data showed no significant treatment effects on soil carbon concentration or soil carbon stock.  A measurable change in soil carbon was not detected during the 1 year between sampling.  In 2009, no significant yield differences were found between species, however the single harvest yields were significantly higher than the split harvest yields by 30 %.  The 2010 yield data showed no effect of harvest frequency yet the Miscanthus yields were 25% higher than the remaining species.   The carbon mass removed in the biomass  followed the same trends as biomass yield.  The data suggest that carbon cycling and sequestration are influenced by species and harvest frequency but that these effects interact with growing season conditions.  Continued monitoring will determine what role species and harvest frequency selection play in the race for sustainable energy production.