Sulfur coated fertilizers and process for the preparation thereof

A process for the preparation of an extended residual, controlled release sulfur coated fertilizer product comprising:

• coating a particulate water-soluble fertilizer core with a primary sulfur coating;
• applying a molten polymeric topcoat over said primary sulfur coating under low shear conditions while said sulfur coating on said fertilizer core is still fresh, said fresh sulfur coating having been cooled to a temperature not less than about 120.degree. F. prior to application of said polymeric topcoat thereover but sufficiently to provide a surface on said fertilizer core having essentially no stress induced discontinuities therein, said sulfur coating containing sufficient amorphous sulfur content at the time said polymeric topcoat is applied thereover to preserve surface integrity of said coating;
• and said molten polymeric topcoat consisting essentially of a water insoluble polymeric film-forming composition having a melting temperature greater than about 120.degree. F. and having membrane-like permeability characteristics;
• and
• solidifying said molten polymeric topcoat applied over said primary sulfur coating to provide an outer encapsulating layer through which said fertilizer is released at a diffusion controlled rate of essentially zero-order such that said fertilizer releases from said primary sulfur coating and said polymeric topcoat essentially linearly over time.

An extended residual, controlled release coated fertilizer product providing for the release of said fertilizer from said coating at a diffusion controlled rate linearly over time, said product comprising:

• a particulate water-soluble fertilizer core having a primary sulfur coating thereon with a polymeric topcoat applied thereover;
• said primary sulfur coating having been fresh at the time said polymeric topcoat is applied thereover, said fresh sulfur coating having been cooled to a temperature not below about 120.degree. F. at the time said polymeric topcoat is applied thereover to provide a surface on said fertilizer core which has essentially no stress induced surface discontinuities therein at the time said polymeric topcoat is applied thereover and said sulfur coating includes a sufficient amorphous sulfur content at the time said polymeric topcoat is applied thereover to preserve surface integrity of said coating;
• and
• said polymeric topcoat being formed from a water insoluble polymeric film-forming composition having membrane-like permeability characteristics for release of said fertilizer at a diffusion controlled rate of essentially zero-order from said primary sulfur coating and said polymeric topcoat such that said fertilizer releases essentially linearly over time.

An extended residual, controlled release coated fertilizer product providing for the release of said fertilizer from said coating at a diffusion controlled rate linearly over time, said product comprising:

• a particulate water-soluble fertilizer core having a primary sulfur coating thereon with a polymeric topcoat applied thereover;
• said primary sulfur coating having been fresh at the time said polymeric topcoat is applied thereover, said fresh sulfur coating having been cooled to a temperature not less than about 120.degree. F. prior to application of said polymeric topcoat thereover but having been cooled sufficiently to provide a surface on said fertilizer core which has essentially no stress induced surface discontinuities therein at the time said polymeric topcoat is applied thereover and said sulfur coating includes a sufficient amorphous sulfur content at the time said polymeric topcoat is applied thereover to preserve surface integrity of said coating;
• and
• said polymeric topcoat being formed from a water insoluble polymeric film-forming composition having a melting temperature greater than about 120.degree. F. and having membrane-like permeability characteristics for release of said fertilizer at a diffusion controlled rate of essentially zero-order such that said fertilizer releases from said primary sulfur coating and said polymeric topcoat essentially linearly over time.