Japanese holly growth and release pattern of ammonium and nitrate from controlled-release fertilizers

Applications of 0.85, 1.70 or 2.55 kg N m^?3 were made to Ilex crenata Thunb. Hetzi. Nitrogen sources included weekly applications of liquid fertilizer (NH₄NO₃) and single application of TVA's Sulfur coated urea (SCUT), Gold N (SCUG), Nitroform (NITR), isobutylidene diurea (IBDU), and an experimental N-containing Osmocote (OSCN). Shoot dry matter and leaf N from recently matured leaves were determined. Analyses of NH₄-N and NO₃-N were also conducted on the monthly leachates collected from the containers. Most controlled-release fertilizers (CRFs) produced greater dry weights at 1.70 kg N, while NH₄NO₃ produced more dry weight than CRF's at 0.85 or 2.55 kg N. Initially, for CRF's ammonium was more abundant than nitrate in the leachate; subsequently, nitrate became the dominant N form for most of the growing-season. All urea-based fertilizers had higher NH₄ levels in the leachate when compared with NH₄NO₃-based fertilizers.