256 THE EFFECT OF VARYING THE N:S BALANCE IN POINSETTIA ON PLANT COLOR RESPONSE AND CONSUMER APPEAL

Abstract

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.