Experimental Design and Species Mixes Used

Experimental Design

The goal of this study was to determine the number and kind of native perennial prairie species to use to maximize biomass production for electrical generation. In May 2009, 48 research plots were sowed with one of four seeding treatments of perennial vegetation: 1) switchgrass monoculture, 2) 5 species of warm-season grasses, 3) ‘biomass mix’-16 species of warm/cool-season grasses and forbs, 4) ‘prairie mix’- 32 species of warm/cool-season grasses, sedges, and forbs (Table 1, click to view PDF). In addition, seeding treatments were replicated on one of three distinct soil groups: 1) 284 Flager sandy loam – somewhat excessively drained alluvial soil, 2) 177/178 Saude-Waukee loam – well drained alluvial soils, and 3) 585 Spillville-Coland complex– poorly drained alluvial soil. All research plots were mowed in early July 2009 to promote prairie plant establishment (Figure 1). Plots were sampled for biomass productivity in mid-September 2009 (Figure 2).



Figure 1. Mowing biomass research plots in the first growing season to improve native plant establishment. Photograph was taken by David O’Shields in late June 2009 at the Cedar River Natural Resource Area in Black Hawk County, Iowa.		Figure 2. Researchers collecting biomass samples in a monoculture switchgrass (Panicum virgatum) plot in September 2009. Photograph was taken by Dave Williams at the Cedar River Natural Resource Area in Black Hawk County, Iowa.

Species Mixes

With hundreds of prairie plant species native to Iowa, choosing which prairie species might be good candidates for biomass production was a large task. The selection process was based on two premises. First, a combination of 16 species of prairie grasses and wildflowers are needed to maximize biomass production (Tilman 2006). Second, native prairie species that we choose for our biomass seed mix be seeded at a rate that is comparable to the recommended seeding rate for switchgrass biomass production. In Iowa, the recommended seeding rate for switchgrass biomass production is 10 pounds per acre or 52 seeds per square foot (Prairie Lands Biomass Project 2011).

The next step was to determine which species should be considered for biomass production. To do this we developed a list of “biomass production criteria” for tallgrass prairie species. A rubric, developed from our criteria list, was used to determine the final 16 species selected for the biomass mix (Table 1, click here for PDF).

The final step was to determine the seeding rate of each species included in the biomass seed mix. This was accomplished through pre-biomass investigations of production plots established on the campus of the University of Northern Iowa (click here for PDF). Seeding rates for each species in the biomass mix was a result of these pre-biomass investigations (Table 2, click here for PDF).

The Biomass Mix - 16 species


Western Wheatgrass Agropyron smithii	Big Bluestem Andropogon gerardii	Side-Oats Grama Bouteloua curtipendula


Canada Wild Rye Elymus canadensis	Virginia Wild Rye Elymus virginicus	Switchgrass Panicum virgatum


Little Bluestem Schizachyrium scoparius	Indian Grass Sorghastrum nutans	Milk Vetch Astragalus canadensis


Showy Tick Trefoil Desmodium canadense	Saw-Tooth Sunflower Helianthus grosseserratus	Ox-Eye Sunflower Heliopsis helianthoides


Round-Headed Bush Clover Lespedeza capitata	Stiff Goldenrod Oligoneuron rigidum	Yellow Coneflower Ratibida pinnata


Compass Plant Silphium laciniatum