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

`Dark Red Annette Hegg' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were grown in a 1 peat : 1 perlite : 1 vermiculite medium using a pinched production schedule with varying N and S fertilizer application rates. Fifty-six treatments consisting of eight N levels (100 to 275 mg·L−1 in 25-mg·L−1 increments) and seven S levels (0 to 75 mg·L−1 in 12.5-mg·L−1 increments) were supplied. Other required nutrients were supplied at commercial recommendations for all treatments. Foliage of each plant was evaluated quantitatively by chromometer readings every 3 weeks. Marketability was determined by sensory evaluations from commercial producers, retailers, and consumers. Results indicated distinct color differences (hue, chroma, value) between S levels of 0 and 12.5 mg·L−1 and a slight difference between S at 12.5 and 25 mg·L−1. The foliage of plants receiving 0 S was lighter, more vivid, and more yellow-green in color. As N levels increased, there was a linear response; foliage became more green, darker, and more dull. Commerical and consumer evaluators rated plants that received S at 0 or 12.5 mg·L−1 at all N levels and plants receiving N at 100 mg L−1 as unmarketable. This research indicates that `Annette Hegg' poinsettia requires S at a minimum of 25 mg·L−1 and N at a minimum of 125 mg·L−1 for commercial acceptance, and commercial N application rates may be greatly reduced when adequate S is supplied.