Sustainable Bioenergy Feedstock Production in Southern Great Plains.

This study describes the findings of a recently completed USDA-DOE BRDi project in Oklahoma. The overall objective of this project is to develop the practices and technologies necessary to ensure efficient, sustainable, and profitable production of cellulosic ethanol feedstocks. This project addresses the needs and concerns of diverse stakeholders both within the cellulosic biorefinery industry and within the public at large. Specific objectives addressed in this presentation are: 1) Develop best management practices (BMP) for sustainable large-scale establishment and production of feedstock crops. 2) Enhance diversity, productivity, and resiliency through development of mixed-species bioenergy production systems. 3) Estimate carbon sequestration and climate change mitigation potential of bioenergy crops. 4) Model spatial variability of biomass yields and soil properties in switchgrass fields of differing growing conditions. Utilizing large-scale feedstock production research, the economic and environmental sustainability of switchgrass, mixed-species perennial grasses, and annual biomass cropping systems was evaluated. Biomass yields yields varied from year to year and with location. The magnitudes of CO₂ and H₂O fluxes were similar at both ecosystems during the active growing periods. Switchgrass ecosystem was a larger carbon sink with a cumulative seasonal carbon uptake of -490 ± 59 g C m^-2 compared to -261 ± 48 g C m^-2 by sorghum. Because the magnitude of CO₂ exchange was similar, the difference in carbon sink strength between two ecosystems was driven mainly by the length of the growing season. ecosystem water use efficiency (EWUE) from 6.3 (March) to 16.1 (June) g CO₂ mm^-1 ET in switchgrass and from 4.7 (May) to 13.6 (June) g CO₂ mm^-1 ET in sorghum, with seasonal averages of 12.6 and 9.9 g CO2 mm^-1 ET for switchgrass and sorghum, respectively. The best estimate of OC could be achieved by systematic sampling, while random sampling maybe the most practical way for estimating switchgrass yields. In conclusion, perennial grasses are more reliable sources of biomass yield under adverse and variable climatic conditions of Oklahoma.