Nutrient Release from Controlled-release Fertilizers in a Neutral-pH Substrate in an Outdoor Environment: I. Leachate Electrical Conductivity, pH, and Nitrogen, Phosphorus, and Potassium Concentrations

Release characteristics of four different polymer-coated fertilizers (Multicote, Nutricote, Osmocote, and Polyon) were studied over a 47-week period in a simulated outdoor, containerized plant production system. The 2.4-L containers, filled with high-fertility, neutral-pH substrate, were placed on benches outdoors to simulate the environmental conditions often used for sun-tolerant, woody perennials grown in the southwestern United States. Container leachates were collected weekly and monitored for electrical conductivity, pH, and concentrations of NH 4 + N, NO 3 - N, total P, and total K. Concentrations of most nutrients in leachates were relatively high, but fluctuated frequently during the first third of the study period, and then gradually decreased and stabilized during the last 27 weeks. Osmocote often resulted in greater NH 4 + and total inorganic N concentrations in leachates than other fertilizers during weeks 1 through 5, whereas Multicote produced higher NH 4 + in leachates than most of the other fertilizer types during weeks 9 through 12. Overall, total P concentrations were greater with Multicote during a third of the experimental period, especially when compared with Osmocote and Polyon. Differences were also observed among treatments for leachate concentrations of K, with Polyon and Multicote fertilizers producing greater K concentrations in leachates compared with Osmocote during several weeks throughout the experimental period. Leachate concentrations of NO 3 - N and P from all fertilizer types were usually high, especially from week 5 through week 30.