Experimental Design and Early Results

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).

Tractor Data collecting
   
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.

First Year Results

The 2009 growing season was a very good for native plant establishment. Precipitation was above average for the spring and summer months without extended periods of dry conditions (NOAA 2010). Emergence and growth of the seeded prairie plants was so vigorous that only one mowing in early July was needed for weed control. By the end of the first growing season, many of the prairie grasses and forbs had flowered and produced seed. Native grasses were lush and virtually weed free in the ‘switchgrass monoculture’ and ‘big five’ grass only plots (Figure 3). By contrast, ‘Biomass’ and ‘Prairie’ plots had a profusion of native forbs that flowered in mid to late summer (Figure 4). This vigorous growth and development of the native plants in this first year of establishment created a rare opportunity for vegetative sampling in mid-September. A preliminary summary of our vegetative sampling for the first year of establishment of this biomass research project is listed below.

Plot 1 Plot 2
   
Figure 3. Switchgrass (Panicum virgatum) monoculture research plot at the Cedar River Natural Resource Area in Black Hawk County, Iowa. Photograph was taken in mid-July 2009 by Jim Mason. Figure 4. Sixteen species “biomass mix” research plot at the Cedar River Natural Resource Area in Black Hawk County, Iowa. Photograph was taken in mid-July 2009 by Jim Mason.

Preliminary Conclusions (from 1st growing season sampling)

  • All prairie species planted in the research project were detected in the first growing season (Table 1, click to view PDF).
  • Overall mean productivity of native plants (as measured by above-ground biomass) was highest (3096 kg/ha) in well drained mesic soil and lowest (1175 kg/ha) in excessively drained dry soils (Table 2, click to view PDF).
  • Mean productivity of switchgrass (Panicum virgatum) was greatest (4481 kg/ha) when planted as a monoculture and in well drained mesic soil (Table 2, click to view PDF).
  • Switchgrass planted as a monoculture produced more above ground biomass (2760 kg/ha) than mixed species plantings in early establishment (Table 3, click to view PDF).
  • When planted as a monoculture, above ground biomass of Switchgrass was significantly lower in dry soils as compared to more moist soil types (Table 2, click to view PDF).
  • Weed productivity (as measured by above-ground biomass) was similar across all seeding treatments in early establishment (Table 3, click to view PDF).

References

National Oceanic Atmospheric Administration (NOAA), 2010. Climatological data for Waterloo, Iowa. Accessed 12/02/2010: http://www.crh.noaa.gov/crh.