Estimation of Spatial, Diurnal, and Species/Varietal Differences in Soil CO2 Efflux From Biofuel Feedstock Plots.

Due to the prospect of  high yielding C-4 tropical grasses, including Pennisetum purpureum (Bana Grass) and Panicum maximum (Guinea Grass), as lignocellulosic feedstocks for biofuel production, an ongoing multi-disciplinary project is investigating the potential of 25 grass varieties as a biofuel feedstock. One aspect of the project is to assess the impact of the feedstock grasses on soil carbon dynamics. One way to characterize soil carbon dynamics is to measure CO₂ efflux from the soil surface. Typically, soil CO₂ efflux composed on half autotrophic and half heterotrophic origins, with great variability in temporal, spatial, and species. Since minute fraction of respiration comes from decomposition of more recalcitrant soil organic matter, it is indicator of changes in plant metabolism and belowground microbial activity. Soil CO₂ effluxes from biofuel feedstock plots were estimated using LI-6400 portable photosynthesis system with soil CO₂ flux chamber (LICOR Biosciences, Lincoln, NE) to determine (1) spatial variability within the 1.2 m by 3 m plot, (2) diurnal efflux fluctuation, and (3) species and varietal differences in fluxes. Spatial variability trial suggested at least 5 replicates were needed to capture the spatial variability of the efflux within plot. The trial for diurnal fluctuation revealed minor fluctuation occurs throughout day, although soil temperature remained relatively constant (less than 3 ¢ªC difference). Soil temperature and efflux were poorly correlated (r²=0.024). The results obtained from these preliminary studies will be used for more comprehensive study to characterize the soil carbon dynamics of grass varieties intended for use as biofuel feedstock production.