Carbon Sequestration and Greenhouse Gas Emissions Associated with Cellulosic Bioenergy Feedstock Production On Marginal Agricultural Lands in the Lower Mississippi Alluvial Valley.

The Lower Mississippi Alluvial Valley (LMAV) has high potential for bioenergy crop production due to its long growing season, well-developed agricultural infrastructure, and central location within the U.S.  Developing viable management systems for growing cottonwood and switchgrass crops for biofuel production on marginal soils of the LMAV would allow productive soils to remain in conventional agriculture to sustain food production capability of the region.  In addition, adding switchgrass and cottonwood to the landscape of the LMAV could improve C sequestration capacity of the region since switchgrass and cottonwood have higher C sequestration potential than conventional agricultural crops. To develop a comprehensive understanding of the potential of switchgrass and cottonwood management systems to sequester C, fluxes of C associated with these cropping/management systems are being monitored throughout harvesting cycles at a variety of sites.  The objective of this project is to monitor : (1) above- and below-ground biomass C, (2) long-term storage forms of C in soil, (3) greenhouse gas emissions, and (4) "carbon costs" of feedstock production and harvesting associated with individual cottonwood and switchgrass crop production as well as agroforests which combine these two crops in one location. We are also comparing C sequestration and greenhouse gas emission of switchgrass and cottonwood cropping systems to that associated with a soybean-grain sorghum rotation in order to elucidate the potential impacts of the conversion of conventional cropping systems to biofuel feedstock production systems on C sequestration.  Results will be presented for measurements of: (1) total C, total N, microbial C, and labile C in soil collected at the end of the 2011 growing season, (2) soil CO₂ emissions collected monthly in 2012, and (3) C in switchgrass, cottonwood, and soybean biomass collected at the end of the 2011 growing season.