Evaluation of Perennial Warm‐Season Grass Mixtures Managed for Grazing or Biomass Production

Abstract

ABSTRACTPerennial warm‐season grasses (WSG) have potential for use as forage in grazing systems and as biomass for bioenergy production. Managing WSG stands for these purposes could affect ecosystems differently. The goal of this study was to evaluate how management of WSG stands, for either grazing or as a bioenergy crop, would impact weedy and sown biomass, community composition, and total soil C pools. Mixtures containing 1, 4, and 10 native species were established in Blacksburg, VA, and managed for grazing or as a biomass crop from 2009 to 2012. Initially, switchgrass (Panicum virgatum L.) monocultures yielded less sown biomass and had more weed pressure than the more diverse mixtures. Grazing promoted weed invasion in all mixtures, especially in 2012 when grazed areas contained over four times more weed biomass than biomass plots. Forage species composition shifted over time, as forbs, which contributed over 50% of herbage mass in the first year, were replaced by WSG. Total soil C was not affected by management or species composition of WSG stands but did increase 17% over 4 yr. The amount of new soil C added by warm‐season species (C4) was higher in 4‐ and 10‐species mixtures, likely the result of greater WSG biomass and cool‐season species (C3) weeds that invaded switchgrass monocultures. Planting diverse WSG mixtures (4 to 10 species) and managing initially for biomass production may help accelerate stand establishment, produce high herbage yields, and reduce weed pressure.