Foliage Removal Influences Sweetpotato Biomass Yields in Hydroponic Culture

Greenhouse studies were conducted to determine the effect of harvesting sweetpotato [Ipomoea batatas L. (Lam.)] foliage tips (terminal 15 cm) on storage root yield, edible biomass index (EBI), and linear growth rate. Plants were grown hydroponically from 15-cm vine cuttings planted in 0.15 × 0.15 × 1.2-m growth channels using a recirculating nutrient film technique system. Nutrients were supplied from a modified half-strength Hoagland solution with a 1 N : 2.4 K ratio. Foliage tips were removed at 14day intervals beginning 42 days after transplanting. Final harvest was at 120 days after planting. At the end of the growing season, harvested foliage tips totaled 225 g/plant (fresh mass). Foliage removal significantly reduced storage root yield, shoot biomass, and linear growth rate expressed on a canopy cover basis. The EBI was higher for plants with foliage removed than for the control. Table 1. Composition of modified half-strength Hoagland nutrient solution.z Solution composition Concn Stock solution (ml•liter–1) 1 M CaCl2 2.0 Sweetpotato is one of eight crops selected by the National Aeronautics and Space Administration as a potential food source for controlled ecological life support systems (CELSSs) for space missions (Hill et al., 1984). Previous work has identified environmental conditions and cultivars for hydroponic production in controlled environments (Bonsi et al., 1992; Hill et al., 1992; Mortley et al., 1991). Sweetpotatoes have a high edible biomass index (EBI) because foliage and storage roots can be consumed. The tender portions of the foliage are an excellent source of vitamins A, B2, and C; Fe; and protein (Villareal et al., 1979). Pace et al. (1985) reported that the nutritive qualities of sweetpotato foliage are similar to those of other traditional green leafy vegetables. If sweetpotato foliage is to be used as a vegetable in CELSS, the timing of removal must be determined carefully to optimize storage root and foliage production. In field studies conducted by Danhiya et al. (1985), storage root yields decreased by 31% to 48% when 25-cm-long shoot tips were removed and by 48% to 62% when the entire shoot was re1000 Received for publication 12 Sept. 1994. Accepted for publication 21 Mar. 1995. Contribution no. 230 of the George Washington Carver Agricultural Expt. Station, National Aeronautics and Space Administration (grant no. NAG10-0024) and U.S. Dept. of Agriculture/Cooperative State Research, Education, and Extension Service (grant no. ALX-SP-1). The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Research Assistant Professor. 2Professor. 1 M NH4H2PO4 0.5