Tuesday, March 24, 2009

Greenhouse and Nursery - Slow Release Fertilizer: Osmocote

This is the seventh in a series on slow release fertilizers. This post contains information on Osmocote.


Production of Osmocote involves the coating of a soluble fertilizer core with a thermoset copolymer of dicyclopentadiene and a glycerol ester (linseed oil) dissolved in an aliphatic hydrocarbon solvent. Nutrient release patterns vary with the amount of coating applied and the substrate used. Coating weights vary from 10 to 20%. Typically, commercial products are blends of different coating weights. Coating substrates include, but are not limited to, urea, potassium sulfate, and ammonium nitrate. Product longevities range from 5 to 16 months, depending on the temperature.

Osmocote products, like most polymer-coated products, release by diffusion through a semipermeable membrane. Water vapor penetrates the resin coating and dissolves the water-soluble fertilizer core. The dissolved nutrients then diffuse back through the coating to the environment. Since temperature influences the rate of diffusion, temperature plays a big role in the nutrient release. The Osmocote market has been mainly limited to commercial ornamental horticulture production, such as nurseries and greenhouses.

Reprinted from Selected Fertilizers Used in Turfgrass Fertilization by J. B. Sartain and J. K. Kruse, University of Florida Extension.

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