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Abstract

A method is described for studying the 3-dimensional distribution of roots grown in a medium consisting of small pieces of glass. After growing to a desired size, the plant is sacrificed by evaporating all water from the media with flowing air. To visualize the undisturbed root system, an immersion oil with the same refractive index as the glass is added to the glass container in which the plant was grown.

Open Access

Abstract

Four cultivars of greenhouse tomato (Lycopersicon esculentum Mill.) were grown in the greenhouse and two cultivars were grown in growth chambers in order to study the effects of root and air temperature on the elemental composition (N, P, K, Ca, and Mg) of leaf tissue. Most of the variation observed in the nutrient composition of leaves was due to air temperature and the cultivar used; only few root temperature effects were significant. Low air temperatures (24°/14°C, 24°/8°, 19°/14°; day/night) resulted in higher N concentrations in the leaf tissue, whereas root temperature had little effect on N. Response to air temperature was similar for P or for N. However, response to high root temperature (27° and 24° in the greenhouse and the growth chamber, respectively) was greater for P than for N. Air and root temperatures had little effect on K concentration in tomato leaves. Consistently high Ca and Mg levels resulted with low air temperatures (24°/8°, 19°/14°, 13°/8°), whereas root temperature had no effect on accumulation of these two nutrients. The incidence of blossom-end-rot in the fruit of all cultivars used in the study was associated with low Ca and Mg levels in the leaf tissue.

Open Access

Rockwool is an excellent growing medium for the hydroponic production of tomato; however, the standard size rockwool blocks [4 × 4 × 2.5 inches (10 × 10 × 6.3 cm) or 3 × 3 × 2.5 inches (7.5 × 7.5 × 6.3 cm)] are expensive. The following experiments were conducted with less expensive minirock wool blocks (MRBs), on rayon polyester material (RPM) as a bench top liner, to reduce the production cost of tomatoes (Lycopersicon esculentum) grown in a limited-cluster, ebb and flood hydroponic cultivation system. Fruit yield for single-cluster plants growing in MRBs [2 × 2 × 1.6 inches (5 × 5 × 4 cm) and 1.6 × 1.6 × 1.6 inches (4 × 4 × 4 cm)] was not significantly different from plants grown in larger sized blocks (3 × 3 × 2.5 inches). When the bench top was lined with RPM, roots penetrated the RPM, and an extensive root mat developed between the RPM and the bench top. The fruit yield from plants on RPM was significantly increased compared to plants without RPM due to increases in fruit size and fruit number. RPM also significantly reduced the incidence of blossom-end rot. In a second experiment, single- and double-cluster plants were grown on RPM. Fruit yield for double-cluster plants was 40% greater than for single-cluster plants due to an increase in fruit number, although the fruit were smaller in size. As in the first experiment, fruit yield for all plants grown in MRBs was not significantly different from plants grown in the larger sized blocks. MRBs and a RPM bench liner are an effective combination in the production of limited-cluster hydroponic tomatoes.

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Cucumbers (Cucumis sativus L. `Vetomil') were grown in rockwool or perlite to evaluate these media for efficient hydroponic cucumber production under Florida greenhouse conditions. Plants were grown using a double-stem training method, and the frequency of irrigations was controlled by a weighing lysimeter for each treatment. In Expt. 1, plants were grown in rockwool with 29% or 17% leaching fraction (LF) and in perlite with a 17% LF. Nitrogen, P, and K concentrations in the complete nutrient solution were 175, 50, and 180 mg·L−1, respectively. In Expt. 2, N, P, and K concentrations were increased to 225, 60, and 225 mg·L−1, respectively. Other nutrient concentrations and LFs remained as in Expt. 1. In Expt. 1, yields (fruit count and total fruit mass) were higher from plants grown in rockwool at 29% LF than from plants grown in rockwool or perlite at 17% LF. However, in Expt. 2, when nutrient concentrations were higher, total fruit mass was greater from plants grown at the lower LF, although there was no difference in fruit number. In both experiments, cucumber yield did not differ when grown at the same LF in either rockwool or perlite. Electrical conductivity (EC) and pH of the nutrient solution from the growing bags were not affected when LFs were decreased. In Expt. 1, the pH and EC ranged from 6.1 to 7.0 and from 0.9 to 1.6 mS·cm−1, respectively, across all treatments. In Expt. 2, pH and EC ranged from 5.3 to 6.9 and from 0.6 to 2.5 mS·cm−1, respectively, across all treatments.

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Four experiments were conducted from 1992 to 1994 to determine the concentrations of N and P required to maximize yields of rockwool-grown cucumbers (Cucumis sativus `Vetomil') trained with a double-stem method. Concentrations of N and P in rockwool slabs were monitored throughout growth of greenhouse-grown cucumbers. The onset and duration of nutrient depletion in the slabs were related to cucumber yield. In Expt. 1, treatment-1 plants received a two-step solution containing N at 90 and 175 mg·L−1 during successive growth phases, while treatment-2 and -3 plants were grown with N at a constant 175 or 225 mg·L−1. Phosphorus was provided at 50 mg·L−1 in all treatments. Treatment 1 was excluded from Expt. 2. In Expts. 3 and 4, plants were grown with N at 225 or 275 mg·L−1 and P at 75 mg·L−1. Onset of N and P depletion (to <10 mg·L−1) in the growing slabs occurred during the early fruiting stage of cucumber, 1 to 8 days before first harvest. The duration of N and P depletion decreased, and cucumber yields increased with increasing N and P concentrations. When plants were grown with N and P at 275 and 75 mg·L1, respectively, N was depleted in the growing slabs during only one experiment and then for only 4 days, and slab P concentration remained >10 mg·L1. Therefore, under Florida conditions, when growing cucumbers in rockwool using a double-stem training technique, N and P should be provided at 275 and 75 mg·L−1, respectively, to minimize depletion of these nutrients from the growing medium.

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Abstract

Boron deficiency symptoms of hydroponically-grown Ficus elastica Roxb. ‘Decora’ included plant stunting, deformation of immature leaves and necrosis of terminal bud. Excessive boron caused the undersides of mature leaves to have brown, circular lesions with chlorotic halos, starting at leaf margins. Affected leaves abscised prematurely. Boron deficiency symptoms of hydroponically-grown Chrysalidocarpus lutescens Wendl. included stunted growth, chlorotic mottling and streaking of leaflets and eventual death of immature leaves and terminal bud. Inflorescences bore necrotic fruits and died prematurely. Toxicity symptoms included leaflet mottle chlorosis and premature death and tip-bum of all leaves.

Open Access

Abstract

Symptoms of zinc deficiency in hydroponically-grown Chrysalidocarpus lutescens H. Wendl. included plant stunting, uniformly chlorotic foliage and very small leaves bearing stubby, clustered pinnae.

Open Access

Abstract

The cultivation of a wide range of ornamental plants in a closed hydrosolaric greenhouse was studied. The hydrosolaric greenhouse was composed of a solar energy harvesting system and a hydroponic system. Energy collected by the greenhouse air from the sun during the day was conserved in the growth solution, which released it during the night. This system was able to maintain the air temperature 6 C above the outdoor temperature during the night. Relative humidity ranged between 85 and 100%, thus providing a favorable environment for tropical foliage plants. Philodendron bipinnatifidum Schott, Gardenia jasminoides Ellis, Ficus benjamina L., F. lyrata Warb., Anthurium andreanum Lind and Brassaia actinophylla Endl. produced under this system were of excellent quality.

Open Access

Abstract

‘Salad Bowl’ and ‘Waldmann’s Green’ leaf lettuce (Lactuca sativa L.) were exposed to photosynthetic photon flux densities (PPFD) of 444 or 889 µmol s–1m–2 for 20 hours day–1 under a diurnal temperature regime of 25°C days/15° nights or 20° days/15° nights. Leaf dry weight of both cultivars was highest under the high PPFD/warm temperature regime and lowest under the low PPFD/cool temperature regime. ‘Waldmann’s Green’ yielded more than did ‘Salad Bowl’ at 889 µmol s–1m–2 and 25° days/20° nights. Under high PPFD, both cultivars yielded better with 25° days/25° nights than with 25° days/20° nights, although relative growth rates were the same under both temperature regimes.

Open Access
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Abstract

A 50% increase in total radiation by extending the photoperiod from 16 to 24 hr doubled the weight of all cultivars of loose-leaf lettuce (Lactuca sativa L.) ‘Grand Rapids Forcing’, ‘Waldmanns Green’, ‘Salad Bowl’, and ‘RubyConn’, but not a Butterhead cultivar, ‘Salina’. When total daily radiation (moles of photons) was the same, plants under continuous radiation weighed 30% to 50% more than plants under a 16 hr photoperiod. By using continuous radiation on loose-leaf lettuce, fewer lamp fixtures were required and yield was increased.

Open Access