Turf and Landscape - Slow Release Fertilizers: Polymer Coated Fertilizers 1

This is the first in a series on slow release fertilizers for turf and landscapes. This post contains information on one of the newer polymer coating technologies.

Reactive Layer Coating. A relatively new coating technology known as reactive layer coating (RLC) polymerizes two reactive monomers as they are applied to the fertilizer substrate in a continuous coating drum. These in situ reactive layer polymerizations form an ultra-thin membrane coating which controls nutrient release by osmotic diffusion. A number of these products are being marketed under the trade name Polyon. These include coated basic fertilizer materials, i.e., urea, potassium nitrate, potassium sulfate, potassium chloride, ammonium sulfate, ammonium phosphate and iron sulfate, in various particle sizes. Coating weights on urea vary from 1.5 to 15%, depending on the release duration desired.

Nutrients are released from Polyon-coated fertilizers by osmotic diffusion. The RLC process permits application of ultra-thin, and hence lower cost, membrane coatings, which distinguishes this technology from many other polymer-coated fertilizers. The coating thickness determines the diffusion rate and the duration of release. Polyon-coated urea at 4% coating (44%N) will release at twice the rate and will have half the duration as an 8% coating (42% N).

During the manufacturing process two polymers react to form a polyurethane coating which is chemically bonded to the fertilizer core. The advantage of RLC technique is that the liquid coating materials can be applied and polymerized to the desired coating thickness in a continuous coating process drum without the need for solvents and associated recovery equipment. As a result, production costs are lower than many of the other commercial polymer-coated fertilizer technologies.

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