Nitrogen Release Characteristics from Controlled-release Fertilizers
in HortScienceSeven nursery grade (8- to 9-month duration), polymer-coated, controlled-release fertilizers (CRF) were topdressed or incorporated to a peat: sand: vermiculite medium to yield the same amount of N per container. The pots were uniformly irrigated with DI water every week. Leachates were collected and analyzed for N (ammonium plus nitrate) concentration. Two distinct N release (NR) patterns were observed over the 180-day experiment. Osmocote 18–6–12FS, Prokote-P 20–3–10, Osmocote 24–4–8HN, and Polyon 25–4–12 exhibited a NR pattern that closely followed changes in average daily ambient temperatures (AT) over the season. This relationship was curvilinear in nature, with NR being highly responsive to AT up to 25°C. Conversely, Osmocote 18–6–12, Nutricote 18–6–8 (270), and Woodace 20–4–12 showed a stable NR pattern over a wider range of AT, with NR rates 30% to 60% lower than those in the temperature-responsive CRF. Incorporation produced significantly higher cumulative N releases than topdressing but without effect on the actual pattern of NR over the season. Regardless of the N formulation in the CRF, >80% of the N recovered in the leachates was in the nitrate form.
