The Effect of Warm-Season Grass Mixtures On Biomass Yield in Marginal Land.

Greater plant diversity is required to meet the needs of multifunctional ecosystems where the goal is increased sustainability, reduced inputs of fertilizer and pesticides, soil protection, and wildlife habitat.  Recently, grass mixtures with higher species diversity were found to increase biomass yields on degraded lands.  The objectives of this study were to identify warm-season grass mixtures with legumes that have optimum productivity with less nitrogen inputs on marginal land for different regions of adaptation.  Four warm-season grass monstands (switchgrass [Panicum virgatum], big bluestem [Andropogon gerardii], prairie cordgrass [Spartina pectinata], and coastal panicgrass [Panicum amarum]), three warm-season grass mixtures with switchgrass, and six warm-season grass mixtures with native legumes (purple prairie clover [Dalea purpurea] and showy tick trefoil [Desmodium canadense]) were established in ‘paired’ field trials (on marginal soil and on prime farmland soil) in NJ, NY, SD, and PA at a grass seeding rate of 11.2 kg PLS ha^-1 in the spring of 2008 or 2009. Two nitrogen treatments (0, 120 kg ha^-1) were applied in the spring of each year. Biomass, tiller density and plant height were collected across locations in 2009, 2010 and/or 2011. No significant differences were observed between fertilized and non- fertilized plots for any measurements. The switchgrass monostands were the tallest plots while big bluestem monostands were the shortest. Most mixture plots were not significantly different from switchgrass monstand plots. Treatments were 48% taller in prime soil compared to marginal soil conditions. Interestingly, there were no statistical differences between treatments for biomass yield suggesting that adding additional species does not reduce biomass yield in comparison to grass monocultures. This research indicates that increasing biodiversity, which may provide additional benefits such as more stable yields, more efficient nutrient use and more resistance to weed invasion, can be accomplished without reducing biomass yields.