EFFECT OF VARYING THE NITROGEN AND SULFUR SUPPLY ON THE FLOWERING OF POINSETTIA

Cuttings of poinsettia (Euphorbia pulchemma Willd. ex Klotzsch 'Dark R ed Annette Hegg') were grown hydroponically to flowering at three leve ls of nitrogen (N) [64, 128 or 256 ppm] in combination with five level s of sulfur (S) [0, 8, 16, 32, or 64 ppm], Plants were kept vegetative for three weeks and then induced to flower using short days. Plants w ere observed weekly for formation of red bracts and cyathia. Leaves an d roots were sampled for N and S content determination every four week s. Treatments receiving no S showed typical foliage S-deficiency sympt oms, flowered later and less completely, weighed less and were shorter than plants growing in treatments containing S. In terms of plant hei ght and dry weight, there were no differences between treatments conta ining 128 or 256 ppm N. Leaf 8 content decreased over time, especially by the end of the experiment, at which time leaf N content had also d ecreased. This indicates that less fertilizer is needed once flowers a pproach anthesis. Root S decreased over time and showed an interaction between N and S. Overall, the N and S combinations that should be use d in future investigations, since they produced plants of commercially saleable quality and had adequate levels of N and 8 in most plant par ts, were 128 ppm N in combination with 16, 32, or 64 ppm S, and 256 pp m N in combination with 8, 16, 32, or 64 ppm S.