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American skullcap (Scutellaria lateriflora L.), a medicinal plant species valued for its sedative properties associated with flavonoids, is generally harvested from the wild. Scientific information on how field cultivation practices affect dry matter yield is lacking in this species. A 2 3 2 3 3 split plot factorial experiment within a randomized complete block design was conducted on a Marvyn loamy sand (fine-loamy, kaolinitic, Thermic Typic Kanhapludults) in Central Alabama to explore effects of light, irrigation, and nutrient application on dry matter yield of American skullcap. Treatment factors were shade (40% shade vs. no shade), irrigation (applied at 30 kPa vs. no irrigation), and nutrients [no added nutrients vs. nutrients added as chemical fertilizer (100 kg nitrogen, 68 kg phosphorus, 42 kg potassium/ha) or chicken litter (100 kg nitrogen, 50 kg phosphorus, and 123 kg potassium/ha)]. Shade formed the main plot units, whereas irrigation 3 nutrient factorial combinations were subplots. Skullcap shoots in experimental plots were harvested four times during the course of the two-year experiment (2007, 2008). All growth variables measured, except percent dry matter, performed better under shade than in full sun. Dry matter yield was increased 45% by shade, 61% by irrigation, and 22% by addition of nutrients. A significant irrigation 3 nutrients interaction was observed at the first and second harvests. Highest yields were obtained with the irrigation + manure and irrigation + fertilizer treatments under shade and the lowest with fertilizer and the control treatments in full sun. Before the advent of synthetic medicines, plants were a main source of medicine (Mannfried, 1993). A resurgence in the use of herbal medicine (Azaizeh et al., 2005) creates a need to cultivate medicinal plants traditionally harvested in the wild. Benefits of cultivation of medicinal plants include uniformity of herbal material and prevention of incorrect identification, adulteration, and loss of the wild gene pool (Azaizeh et al., 2005; Sturdivant and Blakley, 1999). American skullcap (Scutellaria lateriflora L.) was traditionally used by Native Americans to treat many illnesses (Wills and Stuart, 2004). Currently, the herb is mainly used for its sedative properties (Upton, 2009) and is in high demand in the herbal products industry (Brevoort, 1998). American skullcap is naturally found in moist and wooded areas (Awad et al., 2003; Foster and Duke, 2000) and is classified as a facultative wetland plant (USDA, 2011). The plant has been grown successfully in full sun and partial shade (Janke and DeArmond, 2004; Joshee et al., 2002). Most research on American skullcap has focused on identifying and extracting chemical constituents present in the plant tissues (e.g., Awad et al., 2003; Bergeron et al., 2005). Field experiments on Scutellaria baicalensis were reported by Zheljazkov et al. (2007); however, there is no report of agronomic experiments conducted on American skullcap under field conditions in the United States. The two species differ considerably in adaptation, and S. lateriflora is cultivated for aboveground leaves and stem, whereas roots are harvested in case of S. baicalensis. The objectives of this research were to 1) evaluate the potential for American skullcap to be successfully grown under regular farming practices; and 2) determine growing conditions needed to optimize total dry matter yield. Factors tested were light, water, and nutrients. The effect of the growing conditions tested on flavonoid content in skullcap will be reported separately. Materials and Methods Site description and land preparation. The experiment was conducted at the Horticulture Unit of the E.V. Smith Research Center, near Shorter, AL, on a Marvyn loamy sand (fine-loamy, kaolinitic, Thermic Typic Kanhapludults), 2% to 5% slope. Soil pH measured in Dec. 2006 before liming and on 22 Mar. 2007 10 d after liming were, respectively, 5.1 and 5.8 with a cation exchange capacity of 4.6 cmolc·kg . Before tillage, weeds were controlled using 2.1 kg glyphosate herbicide (Roundup) a.i./ha. A preliminary tillage operation was done in Mar. 2007 using a disk harrow. After the first tillage and after liming, five soil samples were taken from each experimental block at a depth of 0 to 15 cm to determine pH and primary nutrients [nitrogen (N), phosphorus (P), and potassium (K)] content. A second tillage operation was done on 9 Apr. 2007 using a RHINO SHV80 rototiller to loosen the soil. Dolomitic limestone was applied at the rate of 2500 kg·ha in Mar. 2007 before the second tillage and before bedding. Chemical fertilizer and chicken litter were hand-broadcasted on respective plots on 6 Apr. 2007 before bedding. An 18-inch wide bedder (Reddick Fumigants, LLC, Williamston, NC) was used to prepare beds and place drip irrigation lines simultaneously on 10 Apr. 2007. Beds were covered with weed guard groundcover manufactured from ultraviolet-resistant black polyethylene to help control weeds while allowing air and water to reach the plant root system. Holes 5 cm in diameter were cut at a spacing of 30 cm 3 30 cm to allow for transplanted seedlings. Pine bark mulch was spread over the fabric to help control weeds between and on beds. On 7 Apr. 2008, immediately after emergence of new foliage in Year 2, the mulch fabric was removed from all plots to allow stolons, which had spread under the fabric, to grow shoots. Experimental design and treatments. The experiment was a 2 3 2 3 3 split plot factorial in a randomized complete block design (r = 4). The shade factor formed the main plot units, whereas irrigation and nutrients were subplots. Subplots measured 1.2 3 6.1 m (7.43 m) and each subplot consisted of 40 plants. Seedlings were spaced 30 3 30 cm, yielding a population density of 53,800 plants/ ha assuming a full stand. Single drip lines 16 mm inner diameter, 250-mm wall, 30-cm spacing between drippers, 340 L/H flow/ 100 m at 0.55 bars pressure were installed down the center of each bed. The two irrigation levels were none and irrigation Received for publication 18 July 2011. Accepted for publication 12 Oct. 2012. We thank the Alabama Agricultural Land Grant Alliance for partial support for this research. To whom reprint requests should be addressed; e-mail shannda@auburn.edu. HORTSCIENCE VOL. 47(12) DECEMBER 2012 1705 applied when soil moisture tension reached –30 kPa. The nutrient factors were an untreated control, chemical fertilizer (100 kg N, 68 kg P, 42 kg K/ha), and chicken litter (100 kg N, 50 kg P, 123 kg K/ha). In Year 2, chemical fertilizer (136 kg N/ha, 125 kg P/ha, 110 kg K/ha), and chicken litter (136 kg N/ha, 68 kg P/ha, 102 kg K/ha) were reapplied based on soil test results. Composted poultry litter organic pelletized fertilizer (4N–2P–3K) from Longwood Plantation, Newington, GA, was used instead of the dried poultry litter used in Year 1. The pelletized poultry litter also provided 102 kg calcium/ha, 17 kg magnesium/ha, 4.42 kg iron/ha, and 2.38 kg·ha of copper, manganese, and zinc. Sun Blocker Commercial Shade Houses (FarmTek, Dyersville, IA) measuring 7.3 m wide – 9.1 m long were assembled on site. Shade covers manufactured from knitted polyethylene fabric to provide 40% shade were placed on top of a steel frame and around the south, west, and east sides of the frame. Shade houses were oriented north– south, whereas plots were oriented east–west. Seedling establishment and husbandry. Seed of S. lateriflora (Horizon Herbs LLC, William, OR) were cold-stratified in moist potting mix at 4 C in the dark for 8 d (15 to 23 Feb. 2007). The potting mix, Sunshine Professional Peat-Lite Mixes # 8/LC 8 by Sun Gro Horticulture Canada Ltd., Vancouver, British Columbia, was used both in flats and multicell trays. The mix was formulated with Canadian sphagnum peatmoss, coarsegrade perlite, coarse-grade vermiculite, dolomitic limestone, gypsum, and long-lasting wetting agent. The flats were transferred to a growth chamber on 23 Feb. 2007, where they were supplied with mist irrigation (Flora-Mist) for 1 min every hour from 0600 HR to 1600 HR. Four 400-W sodium lamps provided a photoperiod of 12 h. The temperature was maintained at 25.5 C. When seedlings reached 5 cm height, they were transferred to the greenhouse on 7 Mar. Individual seedlings were transplanted to 72cell trays between 9 and 13 Mar. After transplantation, day and night temperatures were kept at 24.4 and 21.1 C, respectively. Seedlings were sprinkle irrigated daily. Peter’s 20-10-20 Peat-Lite Special water-soluble fertilizer (Scotts Company, Marysville, OH) was applied twice after transplantation at the rate of 250 mg·L. Seven d before transplanting, seedlings were placed in full sun to harden. They were transplanted to the field during the last week of Apr. 2007. At transplanting, seedlings averaged 12 cm tall with 10 true leaves based on a random sample of five plants per tray. Soil moisture at this location was low and the most recent precipitation of 18.8 mm rainfall was recorded 10 d before transplanting. Soil temperature at 10 cm and air temperature were, respectively, 19.7 and 16.6 C (Alabama Mesonet). Drip irrigation was applied to all treatments until complete establishment of the plants. Dead seedlings were replaced periodically until full stands were obtained. Twenty days after transplanting, on 20 May 2007, driplines were cut from non-irrigated treatments. Four tensiometers, (Irrometer Co., Riverside, CA) were placed at 15-cm depth in fertilized irrigated and fertilized non-irrigated plots under shade and in full sun in Blocks 1 and 3. Tensiometer readings were taken only in irrigated plots in 2008. Soil moisture tension was recorded twice weekly and irrigation was provided to all irrigated plots when soil moisture tension reached 30 kPa in the irrigated treatments. In 2007, 348 mm of rainfall was recorded between planting and second harvest and an estimated 267 mm irrigation water was

Partial Shade, Irrigation, and Added Nutrients Maximize Dry Matter Yield of American Skullcap (Scutellaria lateriflora L.)