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P.P. David, A.A. Trotman, D.G. Mortley, C.K. Bonsi, P.A. Loretan, and W.A. Hill

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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B.A. Kratky

Total salable yields of `Vendor' greenhouse tomatoes produced with 4 non-circulating, hydroponic methods were not significantly different from yields produced with conventional soil bed culture (5.69 kg/plant).

Three methods employed a capillary, sub-irrigated system wherein the plant container rested in a shallow, covered, polyethylene-lined tank containing 5 cm of nutrient solution. Plant containers consisted of 7 and 25 liter plastic pots containing a 1 hapuu:2 cinder medium plus 1 and 2 plants, respectively, and rockwool blocks (7.5 × 7.5 × 6.5 cm) resting on larger rockwool blocks (15 × 15 × 7.5 cm).

The fourth method consisted of rockwool blocks (7.5 × 7.5 × 6.5 cm) resting on a screen placed in a covered, 20 cm deep, polyethylene-lined tank filled with nutrient solution.

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A.A. Trotman, C.E. Mortley, D.G. Mortley, P.P. David, and P.A. Loretan

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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Audrey A. Trotman, P. David, D. Mortley, and J. Seminara

In a greenhouse experiment, the effect of the addition of higher levels of potassium (K) in the replenishment stock used to supply nutrients in a nutrient film technique system was examined. For this study, `TU-82-155' sweetpotato was grown hydroponically for 120 days under four nutrient application/replenishment treatments: 1) REG—solution was changed at 14-day intervals and volume allowed to fluctuate; 2) MHH—replenishment with 10× concentrate of a modified half Hoagland solution (MHH) or with water to regain set volume (30.4 liters) and maintain set point of electrical conductivity (EC, 1050–1500 μmho); 3) MHH + 2K—daily replenishment with 10× concentrate of a modified half Hoagland solution (MHH) or with water to regain the set volume and adjust EC to 1400 followed by application of 50 ml of a 2K stock solution to an EC of 1500; 4) MHH/2K—replenishment with 10× concentrate of a modified half Hoagland solution that incorporated the 2K component or with water to regain set volume (30.4 liters) and maintain set point of electrical conductivity (EC, 105–1500 μmho). The storage root yield (g fresh weight per plant) was significantly higher when the 2K treatment was incorporated with the 10× MHH stock. The storage root yield averaged 324.8 g/plant compared with a yield of 289.6 and 252.9 g/plant, respectively, for the REG and MHH nutrient application protocol. As in earlier experiments, the MHH treatment was comparable to the REG protocol, validating the use of a replenishment approach for nutrient supply in hydroponic sweetpotato culture.

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Bruce Bugbee

There is an increasing need to recirculate and reuse nutrient solutions to reduce environmental and economic costs. However, one of the weakest points in hydroponics is the lack of information on managing the nutrient solution. Many growers and research scientists dump out nutrient solutions and refill at weekly intervals. Some authors have recommended measuring the concentrations of individual nutrients in solution as a key to nutrient control and maintenance. Dumping and replacing solution is unnecessary. Monitoring ions in solution is unnecessary; in fact the rapid depletion of some nutrients often causes people to add toxic amounts of nutrients to the solution. Monitoring ions in solution is interesting, but it is not the key to effective maintenance. During the past 18 years, we have managed nutrients in closed hydroponic systems according to the principle of “mass balance,” which means that the mass of nutrients is either in solution or in the plants. We add nutrients to the solution depending on what we want the plant to take up. Plants quickly remove their daily ration of some nutrients while other nutrients accumulate in the solution. This means that the concentrations of nitrogen, phosphorous, and potassium can be at low levels in the solution (<0.1 mM) because these nutrients are in the plant where we want them. Maintaining a high concentrations of some nutrients in the solution (especially P, K, and Mn) can result in excessive uptake that can lead to nutrient imbalances.

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M.A. Sherif, P.A. Loretan, A.A. Trotman, J.Y. Lu, and L.C. Garner

Nutrient technique (NFT) and deep water culture (DWC) hydroponic systems were used to grow sweetpotao to study the effect of four nutrient solution treatments on: translocation of nutrients and plant and microbial population growth in split-root channels. 'TU-155'cuttings (15 cm) were prerooted for 30 days in sand in 4 cm CPVC pipes 46 cm in length. A modified half Hoagland (MHH) solution was supplied ad libidum. After 30 days, plants were removed and the roots of each plant were cleaned and split evenly between two channels (15 cm deep by 15 cm wide by 1.2 m long). four plants per channel. Nutrient solution treatments (replicated) were: MHH-MHH: MHH-Air, MHH-deionized water (DIW); and monovalent (Mono) - divalent (Dival) anions and cations. Solution samples were continuously collected at 7-day intervals for microbial population profiling. Plants were harvested after growing for 120 days in a greenhouse. Storage roots, when produced, were similar in nutritive components. However, no storage roots were produced in Air or Mono channels and only a few in DIW. Fresh and dry weights for storage roots and foliage were highest in MHH-MHH in both NFT and DWC in repeated experiments. Population counts indicated that nutrient solution composition influenced the size of the microbial population in NFT. Population counts were highest in Dival channels. The microbial population counts (4.20-7.49 cfu/mL) were. relatively high in both NFT and DWC systems.

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Jack W. Buxton and Wenwei Jia

Lettuce was produced using a new concept of hydroponics. The system is based on maintaining a constant water table (CWT). Plants grew on a flat surface and obtained the nutrient solution from capillary matting. One end of the mat was suspended in a trough containing the nutrient solution. The distance between the nutrient solution in the trough and the bench top was kept constant with a water level controller. The nutrient solution was resupplied from a larger reservoir. A ground cover on top of the capillary mat provided nutrient movement to the roots but prevented root penetration. Lettuce seedlings, germinated in small plug trays, were placed in holes cut in a 2.5-cm-thick styrofoam sheet. The styrofoam provided seedling support as well as protected the roots. Roots grew on the surface of the ground cover and were easily removed at harvest. The CWT could be adjusted by changing the height of the water level controller. The CWT concept of hydroponic production does not require pumps nor large storage reservoirs. No runoff occurs; the only nutrient solution used is that required by plants and a minimum amount of evaporation from the ground cover surface. Disease potential should be less than in other systems.

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Jay Frick and Cary A. Mitchell

2-[N-morpholino] ethanesulfonic acid (MES) buffer or Amberlite DP-1 (cation-exchange resin beads) were used to stabilize substrate pH of passive-wicking, solid-matrix hydroponic systems in which small canopies of Brassica napus L. (CrGC 5-2, genome: ACaacc) were grown to maturity. Two concentrations of MES (5 or 10 m m) were included in Hoagland 1 nutrient solution. Alternatively, resin beads were incorporated into the 2 vermiculite: 1 perlite (v/v) growth medium at 6% or 12% of total substrate volume. Both strategies stabilized pH without toxic side effects on plants. Average seed yield rates for all four pH stabilization treatments (13.3 to 16.9 g·m-2·day-1) were about double that of the control (8.2 g·m-2·day-1), for which there was no attempt to buffer substrate pH. Both the highest canopy seed yield rate (16.9 g·m-2·day-1) and the highest shoot harvest index (19.5%) occurred with the 6% resin bead treatment, even though the 10 mm MES and 12% bead treatments maintained pH within the narrowest limits. The pH stabilization methods tested did not significantly affect seed oil and protein contents.

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Stephanie Burnett, Marc van Iersel, and Paul Thomas

Osmotic compounds, such as polyethylene glycol 8000 (PEG-8000), reduce plant elongation by imposing controlled drought. However, the effects of PEG-8000 on nutrient uptake are unknown. Impatiens `Dazzler Pink' (Impatiens walleriana Hook. F.) were grown hydroponically in modified Hoagland solutions containing 0, 10, 17.5, 25, 32.5, 40, 47.5, 55, or 62.5 g·L–1 PEG-8000. Impatiens were up to 68% shorter than control plants when grown with PEG-8000 in the nutrient solution. Plants treated with PEG-8000 rates above 25 g·L–1 were either damaged or similar in size to seedlings treated with 25 g·L–1 of PEG-8000. Impatiens leaf water potentials (Ψw) were positively correlated with plant height. PEG-8000 reduced the electrical conductivity of Hoagland solutions as much as 40% compared to nontreated Hoagland solutions, suggesting that PEG-8000 may bind some of the nutrient ions in solution. Foliar tissue of PEG-treated impatiens contained significantly less nitrogen, calcium, zinc, and copper, but significantly more phosphorus and nickel than tissue from nontreated impatiens. However, no nutrient deficiency symptoms were induced.

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Jonathan M. Frantz and Gregory E. Welbaum

Intensive, deep-batch, hydroponic systems that use float beds (FBs) are used extensively by the tobacco industry to produce transplants. FBs and a modified FB system with separate drying and flooding stages called ebb-and-flood (EF) beds were used to grow 12 diverse horticultural crops to maturity. Beds were filled with 570 L of water with 114 mg·L−1 N and 143 mg·L−1 K or 66 mg·L−1 N and 83 mg·L−1 K in 1994 and 1995, respectively. The EF beds were flooded for 6 hours, then drained for a 6-hour dry stage each 12 hours in 1994, and flooded for 1 hour and dried for 5 hours each 6-hour period in 1995 from May through August. Although both systems were suitable for producing Chinese water spinach (Ipomoea aquatica Forssk.—see footnote in Table 1), vegetable amaranth (Amaranthus tricolor L.), zinnia (Zinnia elegans Jacq.), and sweet basil (Ocimum basilicum L.), the EF system provided greater control over water availability and higher oxygen concentration in the root zone.