Leaf anatomical and nutrient concentration responses to nitrogen and sulfur applications in poinsettia

Abstract

Today the many varieties of poinsettia available for production are typically designated as one of two types: dark leaf vs. green leaf/light leaf types. Research has shown that dark leaf varieties require less fertilizer than green leaf types. The objectives of this research were to evaluate the effect of varying nitrogen (N) and sulfur (S) fertilizer applications on leaf anatomy, essential nutrient elements, and the growth and development of a dark leaf variety of poinsettia. Vegetative "Freedom Red" poinsettias were grown in a soilless mix following a typical production schedule except for fertilization. Plants received N at 50, 100, 200, or 275 mg L-1 in combination with S at 0, 12.5, or 25 mg L-1. Visual observations of plants indicated that "Freedom Red" poinsettia responded differently to various application rates of N and S. Plants inferior in size, form, and color were produced when S was applied at rates of 0 mg L-1 in combination with any level of N and 12.5 or 25 mg L-1 S at 50 or 100 mg L-1 N. Specific N-S ratios of applied nutrients were not a reliable predictor of visual quality. Anatomically, "Freedom Red" leaves were typical of poinsettia, consisting of a single-layer papillate epidermis and a single row of palisade cells. There appeared to be one notable difference among treatment extremes: in treatments receiving 50 mg L-1 N, the length of palisade cells was nonuniform from one cell to the next. Leaf tissue analysis indicated that most of the essential elements were present in sufficient amounts. Nitrogen and S concentrations ranged from below critical level to normal range in direct response to the quantity of each nutrient applied. The application of N affected boron, copper, and chlorine while S had an effect on molybdenum.