Productivity and community composition change in prairie biomass feedstocks

With increasing concerns of climate change and resource usage, there is a growing interest in diverse prairie biomass as a form of alternative energy. In this study, we look at four potential biomass feedstock treatments that were chosen specifically to target high biomass yields and consist of native Iowa tallgrass prairie species. The four feedstocks consist of a one-species monoculture of C4 switchgrass (Panicum virgatum L.), a 5-species mixture of C4-grasses, a 16-species mixture of C3 and C4-grasses, forbs, and legumes, and a 32-species mixture of C3 and C4-grasses, sedges, forbs, and legumes. Four replicate plots (0.33-0.56 ha each) of each feedstock were planted on three different soil types; the Flagler sandy loam (sand), Waukee loam (loam), and the Spillville-Coland complex (clay) for a total of 48 plots. We assessed productivity by harvesting all plant material in ten randomly located 0.3 m2 quadrats within each plot and sorted the biomass into five functional groups (C4-grasses, C3, forb, legume, and unseeded species). All four feedstock mixes produced similar biomass yields and are viable mixes for a high-diversity feedstock. The 32-species treatment produced significantly more biomass than the 5-species treatment. Soil type was correlated to both productivity and community composition. Each feedstock had variable yields depending on soil type. The 16- and 32- species community composition was affected by year. The 16- and 32-species treatments shifted from forb and legume dominant to C4-grasses and unseeded species dominant across the duration of the study. The Switchgrass monoculture had a higher percentage of unseeded species than the other three treatments. These results indicate that feedstocks should be selected based on site specific parameters in order to maximize productivity yield