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Joshua K. Craver and Kimberly A. Williams

An increasing number of greenhouse growers are producing food crops using various types of recirculating solution culture. With nationwide trends toward local, sustainable, and/or organic food production (e.g., Dimitri and Greene, 2012 ), the

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William S. Castle, James Nunnallee, and John A. Manthey

individual plants might be rapidly and efficiently evaluated, thus enabling high-throughput screening for citrus breeders, a clear advantage in plant breeding; and 2) how do the solution culture and soil screening methods compare given that soil is a more

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Osamu Kawabata and Richard A. Criley

MacroMixer, a microcomputer spreadsheet program, offers 15 commonly used nutrient sources for quick formulation of a macronutrient mix in solution culture. The program displays the total concentration of each macro-element and the contribution of each source when the user specifies the desired volume of the mix and the amount of source considered. This program, used with trial and error, eases computational complexity, as sources may contain more than one controlled macro-element.

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Youbin Zheng, Linping Wang, and Mike A. Dixon

Electrolytically generated copper is increasingly used to control diseases and algae in the greenhouse industry. However, there is a shortage of information regarding appropriate management strategies for copper in ornamental crop production. The objectives of this study were to characterize the response of three ornamental crops (Dendranthema ×grandiflorum L. `Fina', Rosa ×hybrida L. `Lavlinger', Pelargonium ×hortorum L. `Evening Glow') to different solution levels of Cu2+ (ranging from 0.4 to 40 μm) and to determine the critical levels above which toxic responses became apparent. The following measurements were used to assess the treatments: leaf chlorophyll fluorescence (Fv/Fm), leaf chlorophyll content, and visible injury of leaf and root. Excessive copper reduced plant root length, root dry weight, total dry weight, root to shoot ratio, leaf area, and specific leaf area in all three species. The critical solution level of Cu2+ that resulted in significantly reduced plant dry weight for chrysanthemum was 5 μm; for miniature rose, 2.4; and for geranium, 8 μm. Plant visible root injury was a more sensitive and reliable copper toxicity indicator than visible leaf injury, leaf chlorophyll content, Fv/Fm, or leaf and stem copper content. Generally, all the species exhibited some sensitivity to Cu2+ in solution culture, with chrysanthemum and miniature rose being most sensitive and geranium being least sensitive. Caution should be taken when applying copper in solution culture production systems.

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Osamu Kawabata and Richard A. Criley

In solution culture experiments, determining the quantity of nutrient sources to dispense in a solution mix is time consuming. When a source contains more than one controlled element (e.g., calcium nitrate [Ca(NO3)2]), a change made to control one element (Ca) requires an adjustment to the other element (N). To ease the computational chore, MacroMixer, an application program for mixing macro-nutrients, was developed using a spreadsheet for microcomputers.

MacroMixer consists of two parts. The first part computes the weight (volume for a liquid) of source necessary to give the target element concentration from each source. The second part computes the total concentration for each macro-element from a set of sources in the final mix. The total volume of the mix is specified at the beginning of program, but it can be changed later. Users can obtain a required weight for each source using the first part to use as a starting value in the second part. Adjustments are made among sources to achieve target element concentrations in the final mix.

The spreadsheet format hides computational formulae and constants for a clear view of solution composition; thus users are encouraged to exercise trial and error to achieve the most balanced mix. Using this program, we quickly formulated 13 mixes used in a 5 K-levels × 5 Ca-levels partial factorial experiment.

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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.

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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.

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H.K. Wutscher

Three trees each of `Valencia' orange (Citrus sinensis L. Osbeck) on rough lemon (C. limon L. Burm. f.) rootstocks that had been grown in solution culture since July 1989 were grown in two solutions from Oct. 1995 to Sept.1996. Solution 1 was a soil extract made by boiling field soil (1:2 soil:water) for 20 min and filtering. Solution 2 was a complete nutrient solution. The solutions were analyzed every 7 days and changed every 28 days. At each solution change, the newly prepared solutions were analyzed for 11 elements and their depletion was determined by weekly analysis. Nearly all the N, K, and Mn in Solution 1 was absorbed in the first 7 days after each solution change; in Solution 2, N and Mn were also absorbed in 7 days, but K absorption was variable; single trees sometimes needed 4 weeks to absorb all the potassium. Calcium and Mg were never completely absorbed and in contrast to Mn, traces of Fe, Zn, and Cu remained in both solutions after 4 weeks.

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Cameron Rees and James Robbins

The iron-efficiency of pin oak (Quercus palustris) and red oak (Quercus rubra) grown in a static solution culture system was evaluated. Treatments included nutrient solutions with no iron, an unavailable iron form (Fe2 O3), and an available iron form (FeEDDHA), each adjusted to a starting pH of 5.5 or 7.0. Both oaks grew better when the available form of iron was used than when the solution contained unavailable or no iron. There was no difference in the height or leaf color for plants of either species when grown with unavailable or no iron. Red oak grown with an available iron form significantly lowered the pH of the solution prior to a growth flush. A similar drop in solution pH was not observed for pin oak growing under similar conditions.

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Cameron Rees and James Robbins

The iron-efficiency of pin oak (Quercus palustris) and red oak (Quercus rubra) grown in a static solution culture system was evaluated. Treatments included nutrient solutions with no iron, an unavailable iron form (Fe2 O3), and an available iron form (FeEDDHA), each adjusted to a starting pH of 5.5 or 7.0. Both oaks grew better when the available form of iron was used than when the solution contained unavailable or no iron. There was no difference in the height or leaf color for plants of either species when grown with unavailable or no iron. Red oak grown with an available iron form significantly lowered the pH of the solution prior to a growth flush. A similar drop in solution pH was not observed for pin oak growing under similar conditions.