Shade, Irrigation, and Nutrients Affect Flavonoid Concentration and Yield in American Skullcap

American skullcap (Scutellaria lateriflora L.) is valued for its sedative properties that are associated with flavonoids. Information on how growing conditions affect flavonoid content is lacking. A 2 by 2 by 3 factorial experiment was conducted in a randomized complete block design (r = 4) with a split-plot restriction on randomization to explore effects of light, irrigation, and nutrient application on flavonoid concentration and yield in American skullcap. Treatment factors were shade (40% shade vs. no shade), irrigation (applied at 30 kPa vs. no irrigation), and nutrients (no fertilizer vs. fertilizer [100 kg N, 68 kg P, 42 kg K ha(-1)] or chicken litter [100 kg N, 50 kg P, 123 kg K ha(-1)]). Shade formed the main plot units; irrigation and nutrients were randomized within subplots. Aboveground biomass was harvested twice in both 2007 and 2008. Dried, finely ground samples were extracted and analyzed for flavonoid concentration using high-performance liquid chromatography (HPLC). The flavonoid baicalin was present in highest concentration and yield, followed by baicalein; wogonin and chrysin were present in only small amounts. Flavonoid concentration was 72% higher in full sun, 15% higher with irrigation, while added nutrients decreased baicalin concentration by 6% but increased baicalein by 16%. Significant interactions of shade. irrigation and shade. nutrients were also observed. Flavonoid yield was 25% higher under shade, 92% higher with irrigation, and 43% higher with added nutrients. Significant interactions of shade. irrigation, shade. nutrients, and irrigation. nutrients were also observed. Increasing biomass yield had a greater effect on total flavonoid harvested than did increasing flavonoid concentration.