Soil Respiration and Microbial Biomass From Switchgrass and Cottonwood Grown As Bioenergy Crops in the Lower Mississippi Alluvial Valley.

Marginal land of the Lower Mississippi Alluvial Valley (LMAV) has the potential to be utilized for the production of bioenergy feedstocks. Increased carbon sequestration in the soil could be an additional benefit of converting marginal lands to bioenergy feedstock production. Soil respiration has a negative effect on the quantity of carbon sequestered in the soil, and has been shown to vary depending on vegetation. Soil respiration is the gaseous emission of carbon dioxide (CO₂) from microbes and plant roots in the soil. The objectives of this study where to evaluate the effects of land use [switchgrass (Panicum virgatum ), cottonwood (Populus deltoides L.), and soybean (Glycine max) cropping systems] on monthly soil respiration and estimated annual CO₂ emissions on a silt loam in east central Arkansas throughout 2012. Soil respiration from all three ecosystems followed the same general trend: increasing from January to May and decreasing from September to December, with peak fluxes occurring in July. However, in June and August there was a decline in soil surface CO₂ fluxes for all three ecosystems. Peak fluxes ranked in the following order: soybean agroecosystem > switchgrass > cottonwood. Annually, soybean had the greatest estimated CO₂ emission from the soil. Switchgrass and cottonwood had 95 and 73%, respectively, of the soybean agroecosystem’s total annual emissions. Results show converting existing cropland on the marginal lands of the LMAV to bioenergy feedstock production would decrease the amount of CO₂ emitted from the soil annually, and these lands could act as valuable carbon sinks.