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  • Author or Editor: D.G. Mortley x
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`Georgia Red' peanut (Arachis hypogaea L.) and TU-82-155 sweetpotato [Ipomoea batatas (L.) Lam] were grown in monocultured or intercropped recirculating hydroponic systems in a greenhouse using the nutrient film technique (NFT). The objective was to determine whether growth and subsequent yield would be affected by intercropping. Treatments were sweetpotato monoculture (SP), peanut monoculture (PN), and sweetpotato and peanut grown in separate NFT channels but sharing a common nutrient solution (SP-PN). Greenhouse conditions ranged from 24 to 33 °C, 60% to 90% relative humidity (RH), and photosynthetic photon flux (PPF) of 200 to 1700 μmol·m-2·s-1. Sweetpotato cuttings (15 cm long) and 14-day-old seedlings of peanuts were planted into growth channels (0.15 × 0.15 × 1.2 m). Plants were spaced 25 cm apart within and 25 cm apart between growing channels. A modified half-Hoagland solution with a 1 N : 2.4 K ratio was used. Solution pH was maintained between 5.5 and 6.0 for treatments involving SP and 6.4 and 6.7 for PN. Electrical conductivity (EC) ranged between 1100 and 1200 μS·cm-1. The number of storage roots per sweetpotato plant was similar for both SP and SP-PN. Storage root fresh and dry mass were 29% and 36% greater, respectively, for plants in the SP-PN treatment than for plants in the SP treatment. The percent dry mass of the storage roots, dry mass of fibrous and pencil roots, and the length-to-diameter ratio of storage roots were similar for SP and SP-PN sweetpotato plants. Likewise, foliage fresh and dry mass and harvest index were not significantly influenced by treatment. Total dry mass was 37% greater for PN than for SP-PN peanut plants, and pod dry mass was 82% higher. Mature and total seed dry mass and fibrous root dry mass were significantly greater for PN than for SP-PN plants. Harvest index (HI) was similar for both treatments. Root length tended to be lower for seedlings grown in the nutrient solution from the SP-PN treatment.

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The effects of elevated CO2 on growth, pod, and seed yield, and gas exchange of `Georgia Red' peanut (Arachis hypogaea L.) were evaluated under controlled environmental conditions. Plants were exposed to concentrations of 400 (ambient), 800, and 1200 μmol·mol–1 CO2 in reach-in growth chambers. Foliage fresh and dry weights increased with increased CO2 up to 800 μmol·mol–1, but declined at 1200 μmol·mol–1. The number and the fresh and dry weights of pods also increased with increasing CO2 concentration. However, the yield of immature pods was not significantly influenced by increased CO2. Total seed yield increased 33% from ambient to 800 μmol·mol–1 CO2, and 4% from 800 to 1200 μmol·mol–1 CO2. Harvest index increased with increasing CO2. Branch length increased while specific leaf area decreased linearly as CO2 increased from ambient to 1200 μmol·mol–1. Net photosynthetic rate was highest among plants grown at 800 μmol·mol–1. Stomatal conductance decreased with increased CO2. Carboxylation efficiency was similar among plants grown at 400 and 800 μmol·mol–1 and decreased at 1200 μmol·mol–1CO2. These results suggest that CO2 enrichment from 400 to 800 μmol·mol–1 had positive effects on peanut growth and yield, but above 800 μmol·mol–1 enrichment seed yield increased only marginally.

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The sweetpotato [Ipomoea batatas (L.) Lam] breeding clone TU-82-155 was grown during Spring 1990 and Summer 1991 in standard Tuskegee Univ. (Alabama) growth channels (0.15 × 0.15 × 1.2 m) for 120 days in a greenhouse using a hydroponic (nutrient film) system with a modified half-strength Hoagland nutrient solution. The nutrient solution was changed every 2, 14, or 28 days. Total N, oil, ash, amino acid, vitamin, and mineral concentrations in storage roots generally were higher and dry weight and starch concentration were lower with 2-day solution changes than with those less frequent.

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In 1991 leafless stem cuttings 7 nodes long from 4 maternal parents (`Carver', Carver ii', `TU-1892' and `Georgia-Jet') and their progenies (MP/P) were planted 3 nodes deep in greenhouse benches filled with Jiffy-Mix to determine if any similarity in storage (SR) or fibrous root (FR) patterns could be used to identify high yielding cultivars in a breeding program. The experiment was planted in a complete randomized block design with 7 replications for each treatment and the total number of SR and FR data were collected over a 9 wk period with weekly sampling. The results indicated that SR initiation was a continuos process and took from 5-9 wk before reaching a maximum level for some MP/P. There was a significant inverse relationship between SR and FR numbers, as SR increased FR decreased. SR for most MP/P were initiated at the underground node closest to the soil surface and FR at the lower two nodes. When regression equations were used on the greenhouse data to predict total number of SR that would be produced in a field trial, no significant differences were found between the number of SR initiated in the greenhouse and field trial 80 days after transplanting by some of these MP/P. However, cultivars with the highest number of storage roots in the field trial did not have the highest number of marketable roots or yield and this was probably due to differences among MP/P in the rate of root enlargement.

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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 14-day 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.

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Growth chamber studies were conducted to determine growth responses of sweetpotato [Ipomoea batatas (L.) Lam) to differing photoperiods (PP) when grown by use of NFT. Four vine cuttings (15 cm length) of GA Jet and TI-155 were grown for 120 days at 12/12, 15/9, 18/6, and 21/3 light/dark PP. Irradiance averaged 427 umol m-2 s-1, with day/night temperatures of 28/22C and 70% RH. A modified half Hoagland's solution was used. Number of storage roots/plant, and storage root fresh and dry weights for GA Jet increased as PP increased from 12 to 21 h, while storage root fresh and dry weights for TI-155 increased up to 18 h PP but declined at 21 h PP. Storage root number/plant for TI-155 declined at 15 h PP but was higher at both 18 and 21 h PP. Highest foliage dry weight for GA Jet was obtained at 21 h PP while that for TI-155 was obtained at 18 h PP. Leaf area index (LAI) for GA Jet increased with increased PP, while LAI for TI-155 increased with increased PP up to 18 h then declined at 21 h PP.

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