Recommended rate of nitrogen application for poinsettia [Euphorbia pulcherrima]

To determine the recommended rate of nitrogen application for pot poinsettia (Euphoria pulcherrima Willd.) production, the characteristics of nitrogen uptake in poinsettia plants grown hydroponically was investigated and the growth curve and total nitrogen uptake in the plants were evaluated throughout the growing period. A cultivar Gutbier V-10 Amy was used. In Exp.-1, rooted cuttings of poinsettia were grown in nutrient solution at 0 + alpha ppm, 100 and 200 ppm of nitrate nitrogen for 24 days. The N concentrations in the culture solution of 100 and 200 ppm plots were adjusted every three days to be kept stable at 100 and 200 ppm, respectively. The plants of 0 + alpha ppm plot did not receive N fro the initial three days, and on the fourth day and every three days thereafter they were supplied with the amount of N absorbed by plants in the 100 ppm plot during the previous 3 days. The N level in the nutrient solution had no effect on the rate of plant growth. While the total amounts of N uptake per increment fresh weight for 24 days in the 100 and 200 ppm plots were not significantly different, the value in the 0 + alpha ppm plot was smaller than those of the other two plots. In Exp.-2, the plants of three plots were grown in long day condition for 30, 15 and 0 days after pinching, and were placed under the short day condition of 6 Sept. The growth curves of the plants in the 3 plots were determined. The total N contents accumulated by them were 604.4, 336.2 and 250.5 mg/plant, respectively. In Exp.-3, the standard curves of the recommended rate of nitrogen application in the 3 types which had 30, 15 and 0 days of long day duration after pinching were derived by calculation of the growth curves, the total N contents in the plants and the N uptake efficiency level. The plants of l15 day and 0 day types fertilized according to the standard curves of recommended N application produced pot poinsettias of excellent quality