Multi-Location Evaluation of Warm-Season Grass Monocultures and Polycultures for Bioenergy.

Perennial warm-season grasses have been considered as feedstock sources for sustainable bioenergy production. It is critical to develop diverse perennial feedstocks and the best agronomic practices for sustainable bioenergy production. Switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus × giganteus) have had considerable attention as bioenergy feedstock due to the high yield potential. Relative little attention has been paid to big bluestem (Andropogon gerardii Vitman) and indiangrass (Sorghastrum nutans (L.) Nash), although they have comparable yield potentials to switchgrass, as well as potentials to adapt environmental niches where switchgrass and Miscanthus may not perform well. In addition to yield potential, ecosystem service is also a very important component for sustainable bioenergy production. System diversity might have greater ecosystem service functions, but it is not necessary to have greater biomass production. The objectives of this study were to compare the biomass production potential of the best commercially available germplasm of native warm-season grass monocultures and mixture at Nebraska and Illinois. Warm-season grasses including big bluestem, indiangrass, switchgrass, sideoate grama and Miscanthus × giganteus were used as plant materials for monoculture and mixture. The effect of species monoculture and mixture on biomass yields was significant for both locations through a 6-year period. In monoculture, the productivity of different warm-season grass species cultivars varied between 8.21 Mg ha^-1 and 16.92 Mg ha^-1 with an overall mean of 9.84 Mg ha^-1 at Urbana, while average annual yields of 9.92 Mg ha^-1 was produced at Mead, ranging from 8.87 Mg ha^-1 to 17.89 Mg ha^-1. There were significant effects of grass species/cultivar combinations in mixtures on biomass yield at Illinois, but not at Nebraska. Our results also indicated that the season pattern of precipitation is a key factor determining biomass yield of big bluestem and indiangrass, not switchgrass.