Improving the viability and sustainability of perennial grasses for bioenergy

The adoption of perennial warm-season grass crops for bioenergy production faces significant social, economic, and agronomic challenges. To overcome these hurdles, three separate studies were completed that evaluated alternative plant breeding and agronomic approaches. The first study evaluated the tradeoffs required for breeding programs to incorporate selection for reduced biomass nitrogen concentration. Biomass Yield and nitrogen concentration had a negative genetic correlation (-0.43), but a 50% increase in biomass yield will result in a 37% increase in nitrogen removal with direct selection for biomass yield. Incorporating the goal of reducing nitrogen concentration into a breeding program would result in improving nitrogen reduction by 225% per cycle as compared to direct yield selection, with only a 26% reduction in biomass yield gains. Reducing nitrogen concentration in biomass will improve quality for use of biomass in a combustion system and have minimal effects on quality in an ethanol conversion system.;An alternative approach to reduce inputs is to incorporate legumes into warm-season grass crops. Once established, red clover addition increased biomass yields in unfertilized swards to levels equivalent to fertilization of 112 kg nitrogen ha-1 and reduced weed cover by 7%. The yield gains with clover addition were consistent regardless of the warm-season grass accession tested and were due to the production of biomass by the clover. The incorporation of legumes in mixtures with perennial warm-season grasses can and should play a part in improving the viability of these cropping systems.;The purpose of the third study was to determine whether increasing genetic diversity can increase biomass yields and reduce weed pressure at the population-level using switchgrass monocultures, big bluestem monocultures, and mixtures of the two species. Genetic diversity was the best predictor of productivity and weed cover, with increased diversity resulting in an increase in productivity of up to 6% and a reduction in weed cover of up to 18.4% in switchgrass and big bluestem monocultures. Only switchgrass genetic diversity was predictive of productivity in species mixtures, but total genetic diversity in species mixtures reduced weed cover by 8.7%.