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Richard V. Tyson, Eric H. Simonne, Danielle D. Treadwell, James M. White, and Amarat Simonne

recirculating aquaculture systems is the biofiltration of fish waste ammonia through nitrification to maintain fish tank water quality ( Gutierrez-Wing and Malone, 2006 ; Masser et al., 1999 ). This is necessary because 10% of the protein in fish feed becomes

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Youbin Zheng, Diane Feliciano Cayanan, and Mike Dixon

The use of a recirculating subirrigation system is becoming increasingly popular in the greenhouse industry. In a survey on the status of nutrient solution recirculation in Ontario, Canada, Richard et al. (2006) found that almost half of the

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Daphne L. Richards and David Wm. Reed

New Guinea impatiens (Impatiens hawkeri Bull.) `Illusion' were grown in a recirculating subirrigation system under various rates and placements of 14N-6.1P-11.6K (Osmocote; Scotts-Sierra, Marysville, Ohio) resin-coated, controlled-release fertilizer (CRF). Four CRF placements (incorporated, top-dressed, bottom, and dibble) were tested. Incorporated placement yielded slightly greater dry weights than the other placements. A rate experiment tested incorporating from 0.5 to 2 times the fertilizer manufacturer's recommended rate of 7.11 kg·m-3. All shoot growth parameters (height, leaf number, shoot, and root fresh and dry weight) exhibited a significant quadratic response, as exemplified by shoot dry weight, where shoot dry weight increased up to the 1.5× rate, after which shoot dry weight decreased. A quadratic response surface model revealed that the optimum rate response ranged from 1.16× rate for height to 1.47× rate for shoot dry weight. The lower bound of the 95% confidence interval (CI) would be the lowest rate at which one could expect maximum growth response. The lower bound of the 95% CI varied from 0.56× rate for height to 1.30× rate for shoot dry weight. Thus, the lowest rate that would be within the 95% CI for all growth parameters, and thus yield maximum growth response, would be the 1.30× rate. Electrical conductivity (EC) of the growing media increased significantly with increasing CRF rate. At all rates, EC was significantly greater in the top layer than in the middle and bottom layers. Only in the 1.75× and 2× rates did EC exceed the recommended EC levels in the middle and bottom layer. All rates >0.75× exceeded recommended EC in the top layer. Release characteristics and total nutrient balance of the CRF was compared in subirrigated and top-watered systems. There was no significant difference between top-watered and subirrigated treatments for the amount of K recovered in plant tops and released from prills. By day 84, in subirrigation, 46% of the K was still in the prills, 41% was recovered in the plant tops, and 22% was recovered in the medium. Similar results were obtained in the top-watering treatment, except that a lesser amount was recovered in the medium (9%) and a small amount (4%) was recovered in the leachate. The uptake of K by plants and release of K by the CRF were inversely proportional and linear with respect to time. Of the K released from the prills, 77% and 83% were recovered in the plant tops for subirrigation and top-watering, respectively, indicating very high fertilizer use efficiency.

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C.L. Mackowiak, R.M. Wheeler, G.W. Stutte, N.C. Yorio, and L.M. Ruffe

Peanut (Arachis hypogaea L.) plants were grown hydroponically, using continuously recirculating nutrient solution. Two culture tray designs were tested; one tray design used only nutrient solution, while the other used a sphagnum-filled pod development compartment just beneath the cover and above the nutrient solution. Both trays were fitted with slotted covers to allow developing gynophores to reach the root zone. Peanut seed yields averaged 350 g·m-2 dry mass, regardless of tray design, suggesting that substrate is not required for hydroponic peanut production.

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Masaru J. Tsujita and G.L. Roberts

This study compared the growth and nutritional status of three rose cultivars (`Jacaranda', `Osiana', `Kardinal') in recycled and non-recycled nutrient systems. The recycled treatment was maintained at an electrical conductivity of 1.8 mS·cm–1 throughout the three crop cycle experiment, whereas the non-recycled treatment allowed the 1.8 mS·cm–1 solution to drain off the troughs. All plants were grown using hydrokorn substrate in 12-liter pots at a temperature of 18C night and 22C day under 24 h supplemental lighting. The first crop cycle showed very little difference in plant growth parameters and foliar nutrient content between the two nutrient delivery methods. By the end of the second crop cycle, foliar N and P were lower in the recycled treatment. Foliar macronutrient concentration was lower in the recycled treatment. By the end of the third crop cycle, plants were visually less vigorous in the recycled treatments. Chloride accumulated in the recycled solution and reached 17 mg·liter–1 by the third crop cycle. Flower yields were lower for `Jacaranda' and `Osiana' in the recycled treatment. Vase life and water uptake of the cut flowers did not differ between the two treatments.

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Norman K. Lownds, Larry S. Kennedy, and Carl E. Sams

Rapid cycling brassica (RCB) plants, because of their short life cycle and ease of growth under laboratory conditions, offer a valuable tool for studying Brassica nutrition. We have been particularly interested in B nutrition in Brassica and, therefore, a hydroponic system was developed to accurately deliver micronutrient concentrations to RCB plants. RCB plants were supported in predrilled holes in the lids of brown 1-L plastic containers. Nutrients were supplied by spraying a modified Hoagland's solution onto the plant roots as they developed inside the containers. This system provided adequate solution aeration for plant growth and allowed analysis of both plant shoots and roots. RCB seeds were pregerminated for radicle emergence, then placed in the holes in the plastic container lids. The effect of B nutrient concentration on B uptake was examined using nutrient solutions containing 0.08, 0.02 and 0.00 ppm added B. Leaf B contents were 139.5, 26.1, and 7.1 g·g–1 for plants grown in 0.08, 0.02 and 0.00 ppm added B, respectively. Effects of drought stress on B uptake and distribution were studied by adjusting nutrient solution osmotic potential using polyethylene glycol (PEG) 8000. PEG-induced drought, (osmotic potential –0.1 MPa) reduced leaf and root B content ≈50% compared to plants grown in nutrient solution only (–0.05 MPa). Boron content in the shoots and pods, however, was not affected by PEG-induced drought stress. These results suggest that this system provides a reliable tool for studying nutrition and drought stress effects using RCB plants.

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Joshua K. Craver and Kimberly A. Williams

greenhouse industry is shifting away from solely producing herbaceous ornamental crops and integrating or replacing these crops with vegetables and herbs. For this reason, hydroponics and other systems using recirculated nutrient solution have become an

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Constantinos Tzerakis, Dimitrios Savvas, Nick Sigrimis, and Georgios Mavrogiannopoulos

There is an increasing need in hydroponic systems to recirculate and reuse nutrient solutions (NS) so as to avoid contamination of groundwater by fertilizer residues and reduce the production cost ( Gutiérrez et al., 2007 ; Van Os et al., 2008

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Yu-Wei Liu and Chen-Kang Huang

environmental factors ( Jones, 2016 ). Hydroponic systems can be divided into recirculating and noncirculating types, depending on how they supply water and nutrients. One limitation of noncirculating hydroponic systems is that they discharge 15% to 40% of their

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Youssef Rouphael, Giampaolo Raimondi, Rosanna Caputo, and Stefania De Pascale

nutrients in closed soilless systems are usually based on the daily control of the EC of the nutrient solution. In this strategy, a crop-specific EC threshold is imposed, and the recirculating nutrient solution is discharged whenever the EC reaches the