Thursday, March 19, 2009

Turf and Landscape - Slow Release Fertilizers: Polymer/Sulfur-Coated Fertilizers

This is the second in a series on slow release fertilizers for turf and landscapes. This post contains information on combination polymer/sulfur coated fertilizers.

Polymer/Sulfur-Coated Fertilizers. Polymer/sulfur coated fertilizers (PSCF) are hybrid products that utilize a primary coating of sulfur and a secondary polymer coat. These fertilizers were developed to deliver controlled- release performance approaching polymer-coated fertilizers, but at a much reduced cost. Sulfur is employed as theprimary coating because of its low cost. Low levels of a polymer surface-coat are used to control nutrient release rate. Unlike the soft wax sealants used to cover imperfections in the sulfur coatings of SCUs, the polymers in this case are chosen to provide a continuous membrane through which water and nutrients must diffuse. The water permeability characteristic of the polymer controls the rate of water diffusion into the particle. The combination of the two coatings permits a positive cost/benefit value over products with singular coatings of sulfur or polymer. They posses excellent abrasion resistance and handling integrity. Since the outer coating is a hard polymer, the products do not leave waxy residues on material handling and application equipment.

The nutrient release mechanism is a combination of diffusion and capillary actions. Water vapor must first diffuse through the continuous polymeric membrane layer. The rate of diffusion is controlled by the composition and thickness of the polymeric film. Once at the sulfur/polymer interface, the water subsequently penetrates the defects in the sulfur coat through capillary action and solublizes the fertilizer core. The solubilized fertilizer then exits the particle in reverse sequence. This diffusion-controlled mechanism permits greater uniformity in nutrient release as compared to the typical matrix release of sulfur-coated fertilizers. The agronomic advantages of this material are reduced surge growth after application and longer residual of up to six months. In addition, the combination coating renders the nutrient release much less temperature sensitive than most polymer-coated fertilizers.

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

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