Chapter 16: Biofuel Feedstock Production: Crop Residues and Dedicated Bioenergy Crops

Burton C. English, University of Tennessee

Daniel F. Mooney, University of Wisconsin

James A. Larson, University of Tennessee

Don Tyler, University of Tennessee

Dustin K. Toliver, Huvepharma, Inc

Today’s economy is primarily based on the use of fossil fuel, but the potential of renewable alternatives, such as bioenergy, is being evaluated. The rationale for this interest centers on climate change, national security and rural development. The United States has increased its production capacity of ethanol, a bioenergy alternative to gasoline, from 1.7 billion gallons in 2000 to 15.5 billion gallons at the beginning of 2017 [70]. Current legislation requires production to increase into the future, and this ethanol will mostly be produced from cellulose [67]. Thus, the use of crop residues for bioenergy and the use of dedicated bioenergy crops are likely to play an important role in the management of conservation tillage systems in the Southeast.

An analysis by English et al. [19] found that 100 million acres of dedicated energy crops would be needed to replace 25 percent of the nation’s energy by 2025. While production is projected to occur throughout the United States, the mid-southern states (Kentucky, Tennessee, Alabama, Mississippi, Georgia and the Carolinas) would produce the bulk of these feedstocks. While dedicated energy crops are one source of cellulose, crop residues may play a role as an energy feedstock as well. In a joint study by the USDA and Department of Energy (DOE) on potential biomass feedstocks, annual production of 75 million dry tons of corn stover and 11 million dry tons of wheat straw were identified as a possible bioenergy feedstock [53].

This chapter examines the potential role of harvesting crop residues and producing dedicated bioenergy crops in conservation tillage systems. When crop residues such as corn stover are left on the soil surface, they provide a number of benefits such as reduced erosion, increased soil organic carbon, improved soil tilth, improved water retention and the recycling of nutrients back to the soil [32]. The benefits of conservation tillage systems are in part based on residues on the soil surface, and removal of the residues would reduce these benefits. Harvesting crop residues could provide another income stream for farmers, but it must be done sustainably and should be weighed against any loss in soil conservation benefits. The other option, planting a dedicated bioenergy crop, may enhance conservation tillage systems. Switchgrass, a perennial bioenergy crop, is well-suited from an agronomic and economic perspective to being planted on marginal cropland. Switchgrass can help reduce erosion, increase soil organic carbon, reduce nutrient leaching and restore soil health. When evaluating switchgrass as a bioenergy feedstock, consider the costs and constraints it may impose on the current cropping system. The remainder of this chapter provides insight on the removal of crop residues and conservation concerns, and includes an in-depth discussion of growing switchgrass as a dedicated bioenergy crop.

Download the tables from Chapter 16.