A pot experiment was carried out at the Fac. of Agric. Nursery, Minia Univ. to explore the response of Delonix regia seedlings to three nitrogen fertilization rates (10, 20 and 30 g/plot of ammonium sulphate (20.5 % N) and seven growth regulator treatments (0, GA₃ at 50, 100 and 150 ppm and IAA at 25, 50 and 75 ppm).
The studied vegetative growth characters (plant height, stem thickness, crown diameter, number of leaves and dry weight of leaves, stem and roots) were gradually increased parallel to the increase in N fertilization rate. A similar trend, in response to N fertilization was observed for total chlorophylls content (a + b) and nitrogen % in the leaves. Concerning growth regulators, both GA₃ and IAA effectively induced different vegetative growth traits and chemical determinations, except, for stem thickness, total chlorophylls and N % which were reduced due to GA₃. The effectiveness of either GA₃ or IAA was parallel to its concentration. The best growth of Delonix regia seedlings was achieved by supplying the plants with the high N fertilization rate (30 g/pot) along with either GA₃ at 150 ppm or IAA at 75 ppm.