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Ellen T. Paparozzi and Kimberly A. Williams

Chat rooms and their use in everyday life are becoming increasingly common, and the technology may be a useful tool to link students with experts of a given subject material and each other. In our shared course Plant Nutrition and Nutrient Management, we experimented with using a chat room to link students with experts in the field of plant nutrition. Our main goal was to enhance the learning experience of the students by providing them with access to national and international plant nutrition researchers. Web CT was used to create and conduct the chat rooms and a chat etiquette evolved to prevent crosstalk and control the flow of the discussions. Positive outcomes of the chat room use included exposure of students to the technology and beneficial interaction between students and experts. Negative aspects of chat room use included the time involved to coordinate the overall effort and train experts to use the technology; the slow pace of some chats; effective grading; and the superficial coverage of some topics. We are developing modifications for future sessions to allow subjects to be explored in more depth and to improve networking between students and experts.

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Li-Chun Huang and Ellen T. Paparozzi

previous studies indicate that there is a significant relationship between the levels of nitrogen and sulfur applied and the growth of floricultural crops. Poinsettia and roses grew well in experiments involving hydroponic solutions that contained reduced nitrogen and some sulfur.

Cuttings of Dendranthema grandiflora cv Dark Yellow Fuji Mefo, were grown in hydroponics with either 64, 127, or 254 ppm N in combination with either 0, 1, 2, 4, 8, 16, 32, 64 ppm S. Plants were grown unpinched and short day treatment started at the end of week 3. Data recorded included symptoms of S deficiency, date of flower initiation, stem length, flower diameter and visual observation of root growth. Color difference of leaves was measured with a chromameter. New leaves and flower heads were taken for sulfur analysis; mature leaves were used for N analysis.

Plants receiving no S showed depressed initiation and development of branch roots, delayed flower initiation, reddened lower leaves and reduced plant growth. Plants receiving some S in combination with any level of N showed good color and acceptable flower diameter and stem length.

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Stacy A. Adams and Ellen T. Paparozzi

Nitrogen and sulfur are macronutrients required by plants to form amino acids used in protein synthesis and other metabolic processes. Commercial poinsettia nutrient recommendations suggest N levels of 350-400 ppm later reduced to 200-250 ppm N. Previous hydroponic research determined that N may be reduced by half if supplied S levels are adequate. The purpose of this study was to look at multiple N and S levels and gauge the effects these combinations had on plant quality.

Poinsettia cv. `Dark Red Hegg' plants, grown in a soilless mix, were fertilized with 56 N and S combinations. N was supplied from 100-275 ppm and S from 0-75 ppm. Plants were evaluated quantitatively by chroma meter readings every three weeks and qualitatively by marketability evaluations from commercial producers, retailers, and consumers.

Results indicate 0 ppm S plant color was more yellow-green than all others. Plants were greener as N increased from 100-150 ppm with no difference above 175 ppm. Evaluators identified plants receiving 0 ppm S and 100 or 125 ppm N as unmarketable. N may be reduced to 175 ppm with no effect on plant quality if adequate S is applied.

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Ellen T. Paparozzi and Robert R. Tripepi

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Mary E. Dale, Ellen T. Paparozzi, and James D. Carr

Cuttings of Euphorbia pulcherrima Willd. ex Klotzsch `Dark Red Annette Hegg' were grown hydroponically in minus S Hoagland's solution modified to supply 0, 1, 2, 4, or 8 mg S/liter for 8 weeks. Nutrient solution changes; visual observations, sampling of tissue, and measurement of electrical conductivity and pH were done every 2 weeks. Deficiency symptoms appeared after 4 weeks of growth in treatments supplying 0 or 1 mg S/liter and occasionally in treatments supplying 2 mg S/liter. Symptoms included reddening of the petiole and main vein of new leaves followed by yellowing of these leaves. Leaf tissue S levels ranged from 700 to 3600 mg S/kg of plant. Deficient levels were identified as <2200 mg S/kg of plant. Suggested critical tissue levels of S would be 2300 to 3000 mg S/kg of plant leaf tissue.

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Willie Helpingstine, Ellen T. Paparozzi, and Walter W. Stroup

Hydrangeas are sold as a potted florist plant during the spring, usually around Mothers Day and Easter. They are considered “heavy feeders” because of their high requirement for nitrogen. Two experiments were conducted to determine if the addition of sulfur (S) would allow lower rates of nitrogen (N) to be applied without sacrificing plant color and quality. Hydrangea macrophylla `Blue Danube' were fertilized with four levels of N (50, 100, 200, and 450 ppm) in combination with six levels of S (0, 6, 12, 24, 48, and 96 ppm) during a typical forcing program. The experimental design was a randomized complete block with a complete factorial treatment design. Data collected included visual observations (using the Royal Horticultural Society Color Chart) on leaf color and uniformity of flower color as well as flower shape. Quantitative data included flower diameter, floret diameter, height, and N an S leaf concentrations. Soil pH was monitored throoughout the experiment and remained fairly constant (range of 5.0–6.0). Additional sulfur seemed to have no effect on leaf color at the higher levels of N. Lower concentrations of N produced more true blue flower color. Also, at lower N concentrations, higher S resulted in larger flowers with larger florets.

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Ellen T. Paparozzi, Joshua R. Widhalm, and M. Elizabeth Conley

Common swedish ivy plants when exposed to nitrogen (N) stress display typical nitrogen deficiency symptoms such as reddening of stems and petioles and yellowing of leaves. When N levels are restored, leaves of swedish ivy plants will re-green without leaf loss. An experiment was conducted to determine how proteins change when leaves were re-greened after N deficiency. Cuttings of Plectranthus australis were rooted under mist and allowed to yellow. Plants were then potted up and fertilized with one of two treatments: complete nutrients with N at 150 ppm or complete nutrients with 0.8 ppm N. The experimental design was a randomized complete-block design with six blocks. Each block had the two N treatments and six plants per treatment. After 3–4 weeks, all plants in the 150-ppm N treatment had re-greened and leaf samples for protein analysis were taken. Plants in four of the six blocks were then switched to the other treatment. After leaves had re-greened once again, leaf samples were taken and the experiment was terminated. Two-dimensional polyacrylamide gel electrophoresis was used to compare the treatments. No obvious differences in protein absence or presence were noted. However, Rubisco appeared to be differentially expressed between the two treatments. 2-D gel analysis with subsequent Western blots showed that for most of the leaf samples, the large subunit of Rubisco (56kD) was quantitatively about 1.3 times more concentrated in the N-deficient plants and possibly modified. The small subunit (12kD) was not reliably detectable. Additional protein results for repeated leaf re-greening and the role Rubsico may play in leaf re-greening will be discussed.

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Walter W. Stroup, Stacy A. Adams, and Ellen T. Paparozzi

An experiment was performed to investigate the effect of various nitrogen sulfer combinations on the quality of poinsettias. After various physiological measurements were taken, commercial growers, retailers, and consumers were asked to evaluate the salability of the plants. In order to avoid evaluator fatigue, only a limited number of plants could be evaluated. This presented both experimental design and data analysis problems. In view of these constraints, and in order to obtain meaningful results, an unreplicated 7 x 8 factorial design was used. Data were analyzed using the method of half-normal plots in conjunction with a modification of the analysis of variance procedure. Rationale and alternative designs will be presented, as well as the step-by-step procedure for using this method as contrasted with the standard ANOVA technique.

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Ellen T. Paparozzi, Walter W. Stroup, and M. Elizabeth Conley

Response surface methods refer to a set of experimental design and analysis methods to study the effect of quantitative treatments on a response of interest. In theory, these methods have a broad range of applicability. While they have gained widespread acceptance and application in manufacturing and quality improvement research, they have never caught on in the agricultural sciences. We propose that this is because there has not been specific research demonstrating their usage. In this paper, two 34 factorial experiments were performed using 100 poinsettia plants (Euphorbia pulcherrima Willd. ex Klotzsch) to measure nutrient element concentrations in leaves at three rates each of nitrogen (N), sulfur (S), iron (Fe), and manganese (Mn). Three different methods of analysis were compared—the standard analysis of variance with no regression model, the quadratic regression model commonly assumed for most standard response surface methods and the Hoerl model regression, a nonlinear alternative to quadratic response. Actual nutrient element values were compared with the values predicted by each regression model and then also evaluated to see if the visual symptomology of yellowing related to those nutrient concentrations in leaves. The Hoerl model demonstrated better ability to detect biologically relevant nonlinear two-, three-, and four-way nutrient interactions. Though there was minimal replication this model characterized the treatment effects while keeping the size of the experiment manageable both in terms of time (labor) and cost of plant analyses. Additionally, it was shown that when S, Fe, and/or Mn were deficient along with N, their visual deficiency symptoms were masked by the overall yellowing associated with N deficiency. This model is recommended as the initial experiment in a series where scientists are looking to expand information already determined for two factors. Other treatment systems that this can be used with include: levels of irrigation, pesticides, and plant growth regulators.

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Li-Chun Huang, Ellen T. Paparozzi, and Carol Gotway

`Dark Yellow Fuji Mefo' chrysanthemums (Dendranthema grandiflora Tzvelev.) were grown hydroponically with either 64, 127, or 254 mg·L-1 N and either 0, 1, 2, 4, 8, 16, 32, or 64 mg·L-1 S in a randomized complete block. Time to flower was measured and symptoms of S deficiency were observed on root, stem, and leaf systems. New leaves and inflorescences were analyzed for S, and lower leaves were analyzed for N concentration. There were four sampling dates and two experiments. Flower diameter was measured when flowers were present, while stem length was measured every sampling date. Nitrogen application could be reduced by half to 127 mg·L-1 as long as some S, 4 mg·L-1 in the fall and 8 mg·L-1 in the spring, was applied. Sulfur deficiency symptoms observed included branchless roots, which aged earlier, overall yellowing of new leaves, and reddening on the leaf abaxial starting from older leaves and moving acropetally. Plants receiving no S had smaller leaves, shorter stems, delayed inflorescence initiation, and restricted inflorescence development. Without S, plants did not produce flowers suitable for commercial sale.