EFFECT OF NITROGEN CONCENTRATION IN CULTURE SOLUTION ON THE GROWTH AND NUTRIENT-UPTAKE BY ROSE PLANTS

Rooted cuttings of rose cv. 'Sonia' were grown in culture solution at various concentra- tions of nitrogen (N) for about a half year, and th e optimal range of N concentration for normal growth, and the relation ship between growth and N uptake were investigated. The N concentratio ns in culture solution were adjusted weekly a 50, 100 or 200 ppm. Plan t growth (FW) was determined by weighing weekly the cut flowers, the s hoots removed by pruning and defoliated leaves (excised parts), and th e other parts, i.e. roots, trunks and old leaves (remaining parts), se parately. The plant FW increased with decreasing N concentration in th e culture solution. The yield (number and weight) and quality of cut f lowers were higher in the solution at low rather than high N concentra tion. The N uptake per 100 g growth in FW decreased with decreasing th e N concentration; plants in 50 ppm N absorbed about 0.7 g N per 100 g growth in FW. Thus, we conclude that for normal growth of rose plants , the N concentration in the nutrient solution should be maintained re latively low. The weight ratio of cut flowers to whole plant in soluti on at 50 ppm N, where the plant growth and cut flower yield were highe st, was 47%. Therefore, to yield 1 kg cut flowers, the plant must incr ease 2.1 kg in FW and absorb 15 g N.