Production and Persistence of Warm-Season Grass Monocultures and Polycultures Managed for Bioenergy.

A common criticism of growing switchgrass (Panicum virgatum) monocultures for Bioenergy is the lack of plant species diversity in the stand. However, switchgrass monocultures are generally perceived to be more productive and provide fewer establishment and management challenges than polycultures. Our objective was to compare the dry matter production and persistence of monocultures and polycultures of native warm-season grasses managed for bioenergy in the Great Plains. This study was conducted in 2004, 2005, 2006, and 2007 at Mead, and Clay Center, NE. Five native warm-season grasses (big bluestem [Andropogon gerardii], indiangrass [Sorghastrum nutans], switchgrass, little bluestem [Schizachyrium scoparium], and sideoats grama [Bouteloua curtipendula]) were seeded in monocultures and polycultures. Monocultures of each species were compared with polycultures consisting of each species at 20% increments in the seeding mixture. Known low-producing polycultures (i.e., 60% sideoats grama + 40% little bluestem) were not seeded. A total of 68 mixtures were seeded in 2004 and 2005 in four replicates at each location for a total of 1,088 plots. Species composition for each plot was determined in autumn 2007. Dry matter production was determined at peak production during the seeding year and for two or three years after seeding, depending on planting year. Stand persistence was measured in spring 2008. Dry matter production patterns and stand persistence for each monoculture or polyculture will provide guidance into what warm-season grasses should be grown to optimize long-term production, maintain quality stands, and potentially increase plant species diversity in stands managed for bioenergy.