Growth and mineral nutrition of Gmelina arborea Roxb. seedlings fertilized with four sources of nitrogen on a latosolic soil

The growth and mineral nutrition of Gnzelina arhorea Roxb. seedlings were investigated in response to four nitrogen-based fertilizers applied at 0, 2.5, 5.0 or 7.5 g N per plant. Nitrogen sources included N&-N as ammonium sulfate, NOs-N as potassium nitrate, NHhNOs-N as calcium ammonium nitrate, and urea-N as urea. Seedlings fertilized with NbNOs-N or urea-N had greater height, collar diameter, dry weight, net assimilation rate, and relative growth rate than seedlings fertilized with NHJ-N or NOj-N. For all sources of nitrogen, increasing the amount of exogenously supplied N per plant promoted shoot growth more than root development, hence the root to shoot ratios of all fertilized seedlings were smaller than those of the unfertilized controls. Applications of NO?-N increased the nitrogen, potassium, and phosphorus concentrations of fertilized seedlings. Regardless of source, a nitrogen application of 2.5 g N per plant was apparently optimal for the growth of Gmelina seedlings on a latosolic soil