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Abstract
Nursery crops are fertilized with nitrogen (N) to enhance their growth and appearance, and crop responses to fertilization vary with form of N supplied and with plant species. This experiment, conducted in a greenhouse, examined privet (Ligustrum ibolium L.) growth and composition as affected by three 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 on privet growth and composition were studied in sand culture. After 240 days of treatment, total growth (mass or shoot extension) of privet did not differ among the three N sources. However, growth increased with increased N concentration with maximum growth occurring between 50 and 250 mg N/L. Although root mass did not vary among the N sources during the experiment, privet grown with ammonium nutrition had more blackened, discolored roots than plants grown with nitrate or mixed nutrition; however, N concentrations above 200 mg/L with each source of N resulted in discolored roots. Concentration of N in privet did not differ with N source but increased as N fertilization 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 solution concentrations above 100 mg N/L. Concentrations of potassium (K), calcium (Ca), and magnesium (Mg) generally were lower in plants grown with all ammonium or mixed nutrition than in plants grown with all nitrate nutrition. Effects of N supply on plant manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), and molybdenum (Mo) varied with N source and plant tissue, with increases of these elements occurring in root tissue of plants grown on ammonium nutrition relative to the other N treatments. This experiment suggests that privet will grow well with nitrate, ammonium, or mixed ammonium-nitrate nutrition. The results also suggest that ammonium nutrition should be monitored more carefully that nutrition with the other sources, because of the acidifying effects of ammonium nutrition on the rhizosphere, effects of ammonium on nutrient accumulation, and root stress imparted by ammonium nutrition.