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  • Author or Editor: D. G. Mortley x
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The effects of 0.25, 1.0, 2.5, 10, and 100 mg/liter of Mn on sweetpotato [Ipomoea batatas (L.) Lam.] were evaluated in 1990 and 1991 by use the nutrient film technique (NFT). A modified half strength Hoagland solution with MnCl2 as the Mn source was used. Foliage and storage root dry weights declined linearly with increasing Mn concentration in whole plants, the decline occurring when Mn concentration approached 1000 ug/g. Storage root growth was severely restricted when Mn concentration in fibrous root reached 200 ug/g while foliage dry weight showed a more moderate decrease. Mn concentration was higher in the foliage than in fibrous roots. Roots of plants showed browning at higher (10 or 100 mg/liter) Mn concentrations in solution, which was stained blue with benzidine and bleached with oxalic-sulfuric acid solution, indicating the presence of oxidized Mn. Characteristic toxicity symptoms were observed in plants receiving 2.5, (moderate) 10 or 100 mg/liter Mn in solution. These results suggest that a Mn concentration of approximately 1000 ug/g in whole plants and 100 ug/g in fibrous roots are critical concentrations with respect to Mn toxicity in sweetpotato.

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Hydroponic growing systems have the potential to maximize phytomass production of peanut (Arachis hypogea) for Controlled Ecological Life Support Systems (CELSS). Two greenhouse experiments were conducted with plant nutrients supplied in a modified Evan's solutionusing a nutrient film technique. The objective of this research was to determine the effect of hydroponic growing systems on pod and foliage yield of `New Improved Spanish' and `Georgia Red' peanut. Sub-objectives were to evaluate (i) the impact of channel size and (ii) the impact of gradation in pore size on the separation of the rooting zone from the zone of gynophore development. The treatments consisted in the first experiment of a wide channel (122 by 15 by 46 cm) fitted with a perforated (3.0mm diam.) PVC grid; a narrow channel (122 by 15 by 15 cm) either fitted with a perforated grid or without a grid. For 'New Improved Spanish' peanut dry foliage yield tended to be higher in the wide channel treatment (0.33 kg/sq m). But the narrow channel yielded the highest mean pod dry weight (0.12 kg/sq m). Pore sizes of the screens ranged from infinity (no screen). perforated grid, square mesh. filtering screen (75u) and solid screen (no pores). For `Georgia Red' peanut, the impact of gradation in pore size of screens was variable: pod number was highest with the filtering (food) screen (216/sq m) but pod dry weight was highest for the square mesh treatment (0.09 kg/sq m). Foliage yield was significantly greater for the filtering (food) screen (1.12 kg/sq m) than in any of the other treatments. The findings of the research indicate that use of screens is feasible and will not retard pod development. The presence of a perforated grid tended to result in lower phytomass production for `New Improved Spanish' peanut.

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The effects of fertilizer placement on growth and nutrient uptake of `Count II' tomatoes (Lycopersicon esculentum Mill.) were evaluated in a 3-year study. Fertilizer was applied broadcast at two rates or banded in two bands at two widths or in four bands, or applied in combinations of sidedressing or broadcasting with banding of N, P, and K at 56, 112, or 224 kg·ha-1 each. Total fruit yield for the 112 kg·ha-1 banded treatment was 24% higher than that for the same rate broadcast and similar to yield for 224 kg·ha-1 broadcast. Treatments involving combined placements, wider bands, or four bands produced yields similar to that for 112 kg·ha-1 banded, but the 56 kg·ha-1 banded with two 56 kg·ha-1 sidedressings had the highest yield. Leaf concentrations and plant contents of N, P, and K and percentage recovery of quantities applied were generally higher in treatments involving banding or sidedressing when compared to broadcasting. Leaf Mn was much higher in banded or sidedressed than for broadcast treatments but was lower when 112 kg·ha-1 was applied in four bands than in two. Only with Mg and Mn were leaf concentrations and plant contents highly correlated. With 112 kg·ha-1 banded, 31.2% of the N, 5.8% of the P, and 44.7% of the K applied were taken up, compared to 12.5%, 2.3%, and 17.2%, respectively, for double this rate broadcast.

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In a greenhouse study, continuous use of the same plant nutrient solution for hydroponic culture of sweetpotato was investigated to determine the effect on storage root yield, plant growth and nutrient solution composition. Plants were grown for 120 days under continuous flow from a 30.4-liter reservoir. Plant growth was compared when nutrient solution was changed at 14-day intervals and when nutrient solution was not changed but nutrients replenished through addition of a Modified half-Hoagland's (N:K=1:2.4) plant nutrient solution when volume in reservoir was -10 liters. Storage root yield was significantly decreased (181 vs 310.3 g/plant) and foliar biomass was significantly increased (372.4 vs 2% g/plant) when nutrient solution was not changed Nitrate and phosphate concentrations decreased in the plant nutrient over the duration of the experiment while sulfate and chloride concentrations increased. Salinity and electrical conductivity were monitored at 2-day intervals and increased with duration of the crop. Increased foliage production may have been the result of nitrogen replenishment going largely for foliage rather than storage root production. It may be that continuous use of the same plant nutrient solution as practiced in this study, resulted in lowered phosphate and nitrate concentrations that limited uptake of these ions by sweetpotato plants, thus reducing yield

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The effect of inoculation of sweetpotato (Ipomea batatas L. (Lam.)) cultivar “TI-82-155” with Azospirillum brasilense was investigated in an observational greenhouse experiment. Sweetpotato was grown in a closed hydroponic system and plant nutrients were supplied in a Modified Half-strength Hoagland's solution (N:K 1:2.4) using a nutrient film technique system (NFT). Plants were either supplied with mineral nitrogen (160 ppm) and noninoculated or were supplied mineral nitrogen (160 ppm) and inoculated. Storage root dry matter was higher under inoculation with A. brasilense. Inoculation also increased the percent total nitrogen in the shoot, leaves, and fibrous root. There was a significant difference in fresh fibrous root weight for the inoculated (262.5 g) over the noninoculated (177.1 g) treatments. Mineral nitrogen supplied in the PNS was not limiting because dry matter for plants inoculated with A. brasilense was not significantly higher than for the noninoculated control.

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The effect of periodic removal of peanut foliage for use as a green vegetable on final foliage and nut production was evaluated in a field experiment in the summer of 1992. Georgia Red peanut cultivar was grown in Norfolk sandy loam soil in a randomized complete block design with four replications. Treatments consisted of removing peanut foliage at 2, 4, and 6 weeks, starting six weeks after planting, and an untreated check. Fresh foliage yield declined an average of 30% while dry weight declined 34% when harvested at 2 and 4 weeks. Nut yield declined 33% when harvested at 2 and 4 weeks but yield decreased only 10% when harvested at 6 weeks. Peanut greens are highly nutritious especially as a rich source of vitamin C and protein. For good balance between foliage and nut production, it appears that harvest intervals should be after four weeks.

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In developing a nutrition management strategy that reduces the quantity of products entering the waste management stream, gaining an understanding of the patterns and fluctuations of nutrient levels and crop growth characteristics is essential. In a greenhouse study, `TU-82-155' sweetpotato was grown hydroponically for 120 days in three nutrient application–replenishment treatments: l) REG-solution changed at 14-day intervals and volume allowed to fluctuate; 2) daily replenishment with 10× concentrate of a modified quarter Hoagland's solution (MQH) or with water to regain set volume (30.4 liters) and maintain set point of electrical conductivity [(EC); 1050 to 1200 μmho]; 3) daily replenishment with l0× concentrate of a modified half Hoagland's solution (MHH) or with water to regain the set volume and maintain the set point of EC. There were no statistically significant differences among nutrient application protocols for storage root count, fresh and dry weights, and percent dry matter. The MHH treatment consistently yielded significantly higher leaf biomass and pencil roots (>1 mm in diameter), indicating a higher potential for increased storage root yield. A nutrient application protocol using treatment 2 has potential for reduced waste production if used in hydroponic sweetpotato production. The plants from the MQH treatment initiated vegetative buds at a significantly later date than in the other treatments and generally showed evidence of suppressed plant development.

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The effects of within-channel spacings (WCS; 13, 18, 25 cm) and between-channel spacings (BCS; 13, 25,38 cm) on yield and linear growth rate of sweetpotatoes [Ipomoea batalas (L.) Lam.] grown by use of the nutrient film technique (NFT) were evaluated. Storage root count, fresh and dry weights, and linear growth rate, expressed as root area, declined linearly in response to decreased BCS, while fresh and dry foliage weight decreased linearly and quadratically as spacing was reduced within the growth channels. Neither linear growth rate on a canopy area basis nor the edible biomass index was significantly affected by WCS or BCS.

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`Georgia Red' peanut (Arachis hypogaea L.) was grown hydroponically at 20/16 °C, 24/20 °C, 28/24 °C, and 32/28 °C, day/night air temperatures to evaluate effects on pod and seed yield, flowering, harvest index, and oil content. Ten-day-old peanut seedlings were transplanted into rectangular nutrient film technique troughs (0.15 × 0.15 × 1.2 m) and grown for 110 days. Growth chamber conditions were as follows: photosynthetic photon flux (PPF) mean of 436 μmol·m-2·s-1, 12 h light/12 h dark cycle, and 70% ± 5% relative humidity. The nutrient solution used was a modified half-Hoagland with pH and electrical conductivity maintained between 6.5 to 6.7, and 1000 to 1300 μS·cm-1, respectively, and was replenished weekly. Vegetative growth (foliage, stem growth, total leaf area, and leaf number) was substantially greater at increasingly warmer temperatures. Reproductive growth was significantly influenced by temperature. Flowering was extremely sensitive to temperature as the process was delayed or severely restricted at 20/16 °C. The number of gynophores decreased with temperature and was virtually nonexistent at the lowest temperature. Pod yield increased with temperatures up to 28/24 °C but declined by 15% at the highest temperature (32/28 °C). Seed yield, maturity, and harvest index were highest at 28/24 °C. Oil content (percent crude fat) increased an average of 23% and was highest at the warmest temperature (32/28 °C). These results clearly suggest that vegetative and reproductive growth, as well as oil content of peanut in controlled environments, are best at warmer temperatures of 28/24 °C to 32/28 °C than at cooler temperatures of 20/16 °C to 24/20 °C.

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Growth chamber studies were conducted to determine if inverse day/night temperature could control canopy height of sweetpotato without adversely affecting storage root yield. Four 15-cm-long vine cuttings of TU-82-155 sweetpotato were grown in rectangular nutrient film technique hydroponic troughs for 120 days. Two troughs were placed into each of six reach-in growth chambers and subjected to 24/18, 26/20, 28/22, 18/24, 20/26, and 22/28 °C, respectively. Growth chamber conditions included a 12/12-h photoperiod, 70% RH, and photosynthetic photon flux of 1000 μmol·m-2·s-1 at canopy level. Total and edible storage root yields were reduced by 50% among plants grown under cool days/warm nights regimes. Harvest index was similar among treatments except for the low value obtained at 22/28 °C. Canopy height was positively correlated with the change in temperature, and for every 2 °C decrease there was a 3.1 centimeter decrease in canopy height. Inverse day/night temperature effectively controlled canopy height but at the expense of storage root production.

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