Soil Efflux and Microbial Dynamics in Bioenergy Crops on Retired Marginal Agricultural Fields in the Lower Mississippi Alluvial Valley.

The Lower Mississippi Alluvial Valley (LMAV) has favorable climate, port access, and infrastructure for producing biofuels.  Two crops being explored for agricultural fields retired from row crop production due to marginally productive soils are switchgrass (Panicum virgatum L.) and eastern cottonwood (Populus deltiodes L.).  At sites in Arkansas and Louisiana, both crops were planted.  A soybean-sorghum rotation was planted as well to provide a comparison of cottonwood and switchgrass with conventional cropping systems in the area.   During a two-year portion of a larger study, soil efflux of CO₂ was measured with static chamber and gas analyzer methods.  Static chambers were also used to measure CH₄ and N₂O efflux.  Soil microbial biomass carbon, labile soil carbon, microbial dehydrogenase activity, and soil carbon concentrations have been measured concurrently with soil efflux sampling.  Results of these measurements will be presented.