Nutrient Release from Controlled-release Fertilizers in a Neutral-pH Substrate in an Outdoor Environment: II. Leachate Calcium, Magnesium, Iron, Manganese, Zinc, Copper, and Molybdenum Concentrations

Nutrient release characteristics of four different controlled-release fertilizers (Osmocote, Nutricote, Polyon, and Multicote) were monitored during an 11-month period in a simulated outdoor nursery production facility. Although no plants were used in the experiment, fertilization rates, irrigation regimes, and cultural practices simulated those typically used to produce fast-growing, high-nutrient-requiring containerized woody ornamentals. Fertilizer prill release characteristics were monitored through analyses of leachates, which were collected weekly. Concentrations of Mg, Mn, Zn, Cu, and Mo were relatively high during the first 5 to 10 weeks of the experiment, then declined and usually stabilized during the remainder of the study. However, Mn and Zn displayed erratic increases in concentrations several times throughout the study. Calcium concentrations did not increase until the fifth week, rapidly peaked to about 300 mg.L(-1), and then decreased and leveled off to approximately equal to 80 to 100 mg.L(-1) during the remainder of the study. Several significant differences were observed between treatments. The Osmocote treatment had significantly greater Ca and Mg concentrations in the leachate than the other fertilizer types during the last 6 weeks of the study, whereas the Nutricote treatment often had significantly greater Fe concentrations than leachates from other treatments, especially during the last 26 to 35 weeks of the study, and significantly greater Zn concentrations than the other CRFs during the last 21 weeks of the study. Based upon U.S. Environmental Protection Agency guidelines, concentrations of Fe were often more than the allowable limit of 0.3 mg.L(-1) with all fertilizer types, but especially with Nutricote. Concentrations of Mn and Cu also exceeded federal guidelines, particularly during the first several weeks of the study.