Carbon Dynamics In Soil Under Continuous Bioenergy Production In Southeastern United States.

Current concerns about carbon cycle include global climate change from increased atmospheric CO₂, and the loss of soil productivity from carbon loss in degraded agricultural soils. Bioenergy production has shown promise to restore C in degraded soil while lessening international oil dependence and help mitigate greenhouse gas emissions. In order to better understand the environmental impacts of crops used for bioenergy production, CO₂ loss and C-sequestration in soils where the bioenergy crops are cultivated is of research interest. Switchgrass and high-diversity grasslands have proven to be efficient at producing both above ground and below ground biomass, thus providing carbon negative fuel (aboveground) and storing soil carbon (below ground).  Carbon dioxide loss from soils to the atmosphere along with carbon storage are the interest in the study due to the need for more thorough research to establish a better understanding of the carbon cycle in soils used for bioenergy production.  To better evaluate soil carbon dioxide flux throughout a day, season, and year, research has been initiated on both switchgrass and pasture in Knoxville, TN. Soil carbon is being evaluated from over 250 sampling locations of switchgrass plots totaling 750 acres across East Tennessee. The main objectives of the study are to 1) compare CO₂ respiration from soil under switchgrass versus grassland production; and 2) use both the soil CO₂ data and the below ground carbon storage data to better understand the soil carbon cycle under bioenergy production. The hypothesis is that CO₂ flux from the switchgrass plots will be more variable than from the pasture due to fertilizer application and dormancy of the switchgrass in the winter months. Also soil carbon storage will increase at lower depths (6-48”) at a greater rate than shallow depths (0-6”) under switchgrass production due to the extensive rooting system that can reach 330 centimeters contributing to the accumulation of organic carbon in lower soil horizons. There are two sites: switchgrass and pasture and each site has three fully automated LICOR LI-8100 long term CO₂ chambers that measure soil CO₂ levels at the soil and atmospheric interface every hour. Changes in soil CO₂ and soil organic carbon will be observed. The long-term goals of this study are to help establish a baseline of carbon dynamics in soils under bioenergy production on a local level, and to help provide more thorough research to establish policy regarding biofuel production.

Keywords: biofuel, bioenergy, CO₂, carbon sequestration, global climate change, greenhouse gas