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Comparison of Cellulosic Ethanol Yields from Midwestern Maize and Reconstructed Tallgrass Prairie Systems Managed for Bioenergy

V. A. Nichols, F. E. Miguez, M. E. Jarchow, M. Z. Liebman, B. S. Dien
BioEnergy research 2014 v.7 no.4 pp. 1550-1560
feedstocks, prairies, continuous cropping, grasses, Zea mays, winter, corn, Secale cereale, soil, rye, ethanol, nitrogen fertilizers, detergents, bioethanol, aboveground biomass, spring, cover crops, corn stover, Midwestern United States
Maize- and prairie-based systems were investigated as cellulosic feedstocks by conducting a 9 ha side-by-side comparison on fertile soils in the Midwestern United States. Maize was grown continuously with adequate fertilization over years both with and without a winter rye cover crop, and the 31-species reconstructed prairie was grown with and without spring nitrogen fertilization. Both maize stover and prairie biomass were harvested in the fall. We compared amounts of cellulosic biomass produced and harvested, carbohydrate contents as measured by both dietary and detergent methods, and estimated cellulosic ethanol yields per hectare. From 2009–2013, the cropping system with the largest non-grain biomass yield was fertilized prairie, averaging 10.4 Mg ha⁻¹ year⁻¹ aboveground biomass with average harvest removals of 7.8 Mg ha⁻¹ year⁻¹. The unfertilized prairie produced 7.4 Mg ha⁻¹ year⁻¹ aboveground biomass, with average harvests of 5.3 Mg ha⁻¹ year⁻¹. Lowest cellulosic (non-grain) biomass harvests were obtained from continuous maize systems, averaging 3.5 Mg ha⁻¹ year⁻¹ when grown with, and 3.7 Mg ha⁻¹ year⁻¹ when grown without a winter rye cover crop, respectively. Unfertilized prairie biomass and maize stover had equivalent dietary-determined potential biomass ethanol yields at 330 g ethanol kg⁻¹ dry biomass, but fertilized prairie was lower at 315. The detergent method did not accurately capture these differences. Over the five-year period of the experiment, unfertilized and fertilized prairie systems averaged 810 and 1,790 L potential cellulosic ethanol ha⁻¹ year⁻¹ more than the maize systems, respectively. Differences in harvested biomass accounted for >90 % of ethanol yield variation.