The GLBRC Switchgrass Biodiversity Experiment (codename SBE) was established in 2023 to examine the beneficial effects of forb composition on productivity, biodiversity, and other ecosystem services provided by switchgrass. In late fall 2023, plots of the former Switchgrass Nitrogen Fixation Experiment (nee Interactions Experiment) were converted from switchgrass monoculture, established in 2016, to varying seeding rates of switchgrass and an 18-speices forb mix targeted to provide 100% switchgrass, 0% forbs (8 lbs/acre switchgrass seed, no forbs); 90% switchgrass (6 lbs/acre switchgrass, 2 lbs forbs); 80% switchgrass (4 lbs/acre switchgrass, 2 lbs forbs); and 60% switchgrass (2 lbs/acre switchgrass, 2 lbs forbs). Plots are 27 m x 40 m and distributed across legacy treatments in a full factorial design with 4 replicate blocks. Each plot is divided into plus N fertilizer and no N fertilizer split plots, with fertilization starting in year 2. See the description of the Interactions Experiment for prior crop history and legacy treatments. In-ground, intact switchgrass mesocosms (0.5 m x 0.5 m x 0.5 m deep) were established in 2018 for use in the Switchgrass Nitrogen Fixation Experiment; six in Plot 6 and two in Plot 8 are still available for use (as of spring 2024). Four in-ground monolith lysimeters (each 1.2 m x 2.2 m x 2.2 m deep) were installed in 1990 and remain intact in Plots 2, 6, 9, and 13.
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