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D. Mortley, P. Loretan, C. Bonsi, W. Hill, and C. Bonsi

An experiment was conducted in environmental growth chambers to study the response of sweet potato to relative humidity (RH). Twenty-four vine cuttings of `TI-155' sweet potato were planted in growth channels in a modified half Hoagland's solution using the nutrient film technique. Plants were exposed to constant RH levels of 50% or 85%. Temperature regimes of 20/22 C were maintained during the light/dark periods with an irradiance level of 600 umol m-2 s1, and a 14 hr/10 hr photoperiod. Plants were harvested 120 days after planting and yield data was taken. High RH (85%) resulted in significant increases in number of storage roots/plant, storage root fresh and dry weight, single leaf photosynthesis and stomatal conductance than at 50% RH. Foliage dry weight and leaf temperature was higher at 50% than 85% RH.

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C. Morris, D. Mortley, P. Loretan, C. Bonsi, and W. Hill

The potential of the sweet potato as a food source for future long-term manned space missions is being evaluated for the National Aeronautics and Space Administration's (NASA) Controlled Ecological Life Support System (CELSS) Program. Several experiments have shown that the sweet potato can be grown hydroponically. However, an evaluation of the NASA fan-shaped Biomass Production Chamber (BPC) channel was initiated to determine if channel depths influenced the yield of hydroponically grownsweet potatoes. Three channel depths were studied, 5 cm (2 in) standard NASA BPC channel, 10 cm (4 in) channel and 15 cm (6 in) channel. The experiment consisted of one replication. The results show that channel depth does effect the yield of storage roots. The 15 cm depth channel provided the most consistent yield with all channels having significantly different fresh storage root yields in the replicate.

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P.P. David, C.K. Bonsi, and D.Z. Douglas

A study was initiated in an environmental growth room to examine the effects of container size on the growth of several sweetpotato genotypes grown under a nutrient replenishment protocol. Plants were grown from vine cuttings of 15 cm in length, planted in 0.15 × 0.15 × 1.2-m growth channels using a closed nutrient film technique system. Nutrient was supplied in a modified half-strength Hoagland's solution with a 1 N: 2.4 K ratio. Nutrient replenishment protocol consisted of daily water replenishment to a constant volume of 38.4 liters in the small reservoir and 345.6 liters in the large reservoir. Nutrients were replenished as needed when the EC of the nutrient solution fell below 1200 mhos/cm. The design used was a split-plot with the main plot being container size and genotypes the subplot. Nine genotypes were evaluated: J6/62, J6176, J8/1, PX/6, PX/10, PX/36, TU-82-155, TU-J1, NCC58. Results showed no effect of container size on storage root yield, foliage fresh and dry mass, leaf area, or vine length. However, plants grown in the large container accumulated more storage root dry mass than those in the small container. All genotypes evaluated showed variation in their responses for all parameters measured.

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DESMOND MORTLEY, V. KHAN, C. BONSI, and E. RHODEN

Fertilizer placement under plastic was studied on 2 tomato cultivars (`TI-130' and `Floradade') during 1989. Treatments were 1, 2 or 3 increments of fertilizer broadcast, banded, broadcast/banded of banded with 1 or 2 sidedressings and a check. Fertilizer applied was NPK at 135-90-84 kg·ha-1 as a ammonium nitrate, triple superphosphate and muriate of potash, 10cm to each side of the plants and 10cm deep. Vine, total, marketable and early yields for lower rates either Br or Ba were as good as those of the full rate Br or Ba with 2 sidedressings (Ba/SD2). Leaf N, P, K, Ca and Mg for `TI-130' were not affected by placement. The Ba/SD2 placement Increased leaf N for `Floradade' but leaf Ca was reduced in all treatments vs the check. Leaf Mn was increased markedly by placements involving broadcasting at all rates.

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P.P. David, C.K. Bonsi, E. Bonsi, R.D. Pace, O. Clark, and L.C. Garner Carva

The effects of sequential foliage topping on two sweetpotato [Ipomoea batatas (L) Lam cvs Georgia Jet, TU-82-18921 cultivars were investigated in a field trial. Three initial foliage cuttings (15 cm cutting from the growing tip) were initialed at 45.60 and 75 days after planting (DAP). Each initial cutting date was followed by zero, one or two cuttings at biweekly intervals.

Total storage root yields were not affected by cutting treatments regardless of the cultivar investigated. Both cultivars differed in their response in dry matter accumulation, while Georgia Jet was not affected by cutting treatments, TU-82-1892 accumulated less dry matter when foliage tips were removed twice during the growth cycle (75.90 DAP) compared to all other cutting treatments.

The amount of foliage tips removed from each cultivar differed significantly over all treatment levels with Georgia Jet producing more foliage tips than TU-82-1892. However. production of foliage tips for both cultivars was greatest when foliage cutting was delayed until 75 DAP.

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D.G. Mortley, P.A. Loretan, C.K. Bonsi, W.A. Hill, and C.E. Morris

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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D.G. Mortley, C.K. Bonsi, P.A. Loretan, W.A. Hill, and C.E. Morris

Growth chamber experiments were conducted to study the physiological and growth response of sweetpotato [Ipomoea batatas (L.) Lam.] to either 50% or 85 % relative humidity (RH). Vine cuttings of T1-155 were grown using the nutrient film technique in a randomized complete-block design with two replications. Temperature regimes of 28/22C were maintained during the light/dark periods with irradiance at canopy level of 600 μmol·m-2·s-1 and a 14/10-hour photoperiod. High RH (85%) increased the number of storage roots per plant and significantly increased storage root fresh and dry weight, but produced lower foliage fresh and dry weight than plants grown at 50% RH. Edible biomass index and linear growth rate (in grams per square meter per day) were significantly higher for plants grown at 85 % than at 50% RH. Leaf photosynthesis and stomatal conductance were higher for plants at 85 % than at 50% RH. Thus, the principal effect of high RH on sweetpotato growth was the production of higher storage root yield, edible biomass, growth rate, and increased photosynthetic and stomatal activity.

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D.G. Mortley, C.K. Bonsi, P.A. Loretan, W.A. Hill, and C.E. Morris

Growth chamber experiments were conducted to study the physiological and growth response of peanut (Arachis hypogaea L.) to 50% and 85% relative humidity (RH). The objective was to determine the effects of RH on pod and seed yield, harvest index, and flowering of peanut grown by the nutrient film technique (NFT). `Georgia Red' peanut plants (14 days old) were planted into growth channels (0.15 × 0.15 × 1.2 m). Plants were spaced 25 cm apart with 15 cm between channels. A modified half-Hoagland solution with an additional 2 mm Ca was used. Solution pH was maintained between 6.4 and 6.7, and electrical conductivity (EC) ranged between 1100 and 1200 μS·cm–1. Temperature regimes of 28/22 °C were maintained during the light/dark periods (12 hours each) with photosynthetic photon flux (PPF) at canopy level of 500 μmol·m–2·s–1. Foliage and pod fresh and dry weights, total seed yield, harvest index (HI), and seed maturity were greater at high than at low RH. Plants grown at 85% RH had greater total and individual leaflet area and stomatal conductance, flowered 3 days earlier and had a greater number of flowers reaching anthesis. Gynophores grew more rapidly at 85% than at 50% RH.

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C. Stevens, V. A. Khan, A. Y. Tang, C. K. Bonsi, and M. A. Wilson

A three year study involving solar heating of soil (soil solarization) with clear polyethylene mulch demonstrated for two years, control of root-knot nematodes (Meloidogyne incognita). The population of M. incognita was reduced >90% in the 0-30cm depth of solarized soil. The number of eggs per gram root recovered and the root gall index from `Georgia-Jet' sweetpotatoes were reduced (92-98%) by soil solarization. Growth and yield were enhanced in solarized soil. The beneficial effects of solarization was observed in the second year following two additional cropping cycles of collard greens and sweetpotatoes.

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D.G. Mortley, P.A. Loretan, W.A. Hill, C.K. Bonsi, and C.E. Morris

Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes (`Georgia Jet' and the breeding clone TI-155) were grown at 12-, 15-, 18-, and 21-h light/12-, 9-, 6-, 3-h dark cycles, respectively, to evaluate their growth and elemental concentration responses to duration and amount of daily lighting. Vine cuttings (15 cm long) of both genotypes were grown in rectangular nutrient film technique channels for 120 days. Conditions were as follows: photosynthetic photon flux (PPF) mean 427 μmol·m–2·s–1, 28C day/22C night air cycle, and 70% ± 5% relative humidity. The nutrient solution used was a modified half-strength Hoagland's solution. Storage root count per plant and per unit area, yield (in grams per square meters per day), and harvest index increased, while production efficiency (in grams per mole) decreased with increased daily PPF. Stomatal conductance for both genotypes declined with increased daily PPF. Leaves were smallest for both genotypes at the 21-h light period, while storage root yield declined as leaf area index increased. Except for a linear decrease in leaf N and K with increased light period, elemental concentration was not significantly influenced.