Soil Gas Efflux in Perennial Bioenergy and Conventional Agricultural Crops in the Lower Mississippi Alluvial Valley

ABSTRACTThe Lower Mississippi Alluvial Valley (LMAV) has favorable attributes for producing biofuels. Two study sites were established on retired agricultural fields in the LMAV to explore switchgrass (SWITCH) and eastern cottonwood (CTWD) as biofuel feedstocks. A soybean-sorghum rotation (CROP) was also established as a conventional cropping system. Soil efflux gas (carbon dioxide [CO2], methane [CH4], and nitrous oxide [N2O]), microbial biomass carbon (Cmic) and dehydrogenase activity were measured for two years. Cumulative growing-season soil CO2 efflux of SWITCH exceeded that of CROP; SWITCH had higher daily CO2 efflux than CTWD and CROP in some months. SWITCH and CTWD had greater Cmic than CROP at both sites. Soil CH4 and N2O efflux rates were low for much of the study, with only short-term differences in soil CH4 observed. Converting these retired agricultural sites to SWITCH increased soil CO2 efflux relative to CROP, with increases attributable to greater plant and microbial respiration.