The effects of nitrogen source and concentration on the growth and mineralcomposition of privet

Nursery crops are fertilized with nitrogen (N) to enhance their growth and appearance, and crop responses to fertilization vary with form of N supplie d and with plant species. This experiment, conducted in a greenhouse, exami ned privet (Ligustrum ibolium L.) growth and composition as affected by thr ee N sources: 100% of the N as nitrate, 100% of the N as ammonium and a 50% -50% mixture of nitrate-N and ammonium-N. Nine different concentrations (in treatments incrementally ranging 0 to 300 mg N/L) of the three N regimes o n privet growth and composition were studied in sand culture. After 240 day s of treatment, total growth (mass or shoot extension) of privet did not di ffer among the three N sources. However, growth increased with increased N concentration with maximum growth occurring between 50 and 250 mg N/L. Alth ough root mass did not vary among the N sources during the experiment, priv et grown with ammonium nutrition had more blackened, discolored roots than plants grown with nitrate or mixed nutrition, however, N concentrations abo ve 200 mg/L with each source of N resulted in discolored roots. Concentrati on of N in privet did not differ with N source but increased as N fertiliza tion increased. Critical N concentration was 3.35% in leaf tissue, 2.40% in stem tissue, and 1.94% in root tissue and was obtained from fertilizer sol ution concentrations above 100 mg N/L. Concentrations of potassium (K), cal cium (Ca), and magnesium (Mg) generally were lower in plants grown with all ammonium or mixed nutrition than in plants grown with all nitrate nutritio n. Effects of N supply on plant manganese (Mn), iron (Fe), zinc (Zn), coppe r (Cu), and molybdenum (Mo) varied with N source and plant tissue, with inc reases of these elements occurring in root tissue of plants grown on ammoni um nutrition relative to the other N treatments. This experiment suggests t hat privet will grow well with nitrate, ammonium, or mixed ammonium-nitrate nutrition. The results also suggest that arnmonium nutrition should be mon itored more carefully that nutrition with the other sources, because of the acidifying effects of arnmonium nutrition on the rhizosphere, effects of a mmonium on nutrient accumulation, and root stress imparted by ammonium nutr ition.