Effects of Plant Diversity and Biochar on the Composition and Yields of Biofuel Grasslands.

Native perennial grasslands have strong potential as a sustainable bioenergy resource that can provide additional ecosystem services, including providing wildlife habitat and improving soil quality. Evidence suggests that higher levels of plant species diversity can improve biomass yields and yield stability. Studies have also shown that the addition of biochar to soils can increase biomass yields, improve soil water retention, and sequester carbon. We examined changes in plant community establishment and biomass yields in plots sown with three different native perennial plant mixtures (switchgrass, low diversity, and high diversity) and applied biochar to half of each plot. The experiment was established in southwest Iowa in 2012. Biochar had a temporary effect early in the growing season, as plots with biochar had a higher weed relative cover and lower sown species relative cover, but this disappeared later in the season. In contrast, plant mixture affected species composition and plant biomass, with switchgrass and low diversity plots containing fewer weeds and more sown plant biomass. By the third year, switchgrass plots had the highest peak dry sown biomass (8.7 Mg ha-1) and lowest weed biomass (2.2 Mg ha-1), followed by low diversity plots (5.0 and 3.3 Mg ha-1, respectively). High diversity plots contained less than 1.0 Mg ha-1 sown biomass and almost 6.7 Mg ha-1 weedy biomass. These data suggest that by the end of the third growing season, switchgrass and low diversity plots yield similar amounts of sown and weedy biomass, and that biochar has no permanent effects on species composition or yields.