Controlled release fertilizer composition

1. A controlled release fertilizer composition comprising a core of urea, the core coated with, in series proceeding from the core outward, a thermoset polymer layer, a wax layer, and a layer consisting of elemental sulfur.

2. The controlled release fertilizer composition of claim 1 comprising an outer wax layer.

3. The controlled release fertilizer composition of claim 2 , wherein the urea is about 43% N on a weight basis, the thermoset polymer layer is about 1.8% on a weight basis, the wax layer is about 0.3% on a weight basis, the layer of elemental sulfur is about 3.8% on a weight basis and the outer wax layer is about 0.5% on a weight basis.

4. The controlled release fertilizer composition of claim 2 , wherein the urea is about 43% Non a weight basis, the thermoset polymer layer is about 2.5% on a weight basis, the wax layer is about 0.3% on a weight basis, the layer of elemental sulfur is about 2.2% on a weight basis and the outer wax layer is about 0.5% on a weight basis.

5. The controlled release fertilizer composition of claim 1 , wherein the thermoset polymer layer comprises a blend ofpolymeric MDI (4,4 diphenylmethane diisocyanate), and a mixture of TEA (triethanolamine) and DEG (diethylene glycol) polyols.

6. The controlled release fertilizer composition of claim 1 , wherein the wax layer comprises an intermediate wax, a paraffin wax, an alpha-olefin wax, or a combination thereof.

7. The controlled release fertilizer composition of claim 2 , wherein the outer wax layer comprises an intermediate wax, a paraffin wax, an alpha-olefin wax, or a combination thereof.

8. A method of producing a controlled release fertilizer composition comprising,

coating urea with two or more than two precursor compounds reactive to form a thermoset polymer layer,

applying a wax onto the thermoset polymer layer, and

spraying molten sulfur onto the wax layer to form a sulfur layer.

9. The method of claim 8 , wherein after the step of spraying molten sulfur, an outer wax layer is applied over the sulfur layer.

10. The method of claim 9 , wherein the thermoset polymer layer comprises a blend of polymeric MDI (4,4 diphenylmethane diisocyanate), and a mixture of TEA (triethanolamine) and DEG (diethylene glycol) polyols.

11. The method of claim 8 , wherein the wax layer comprises an intermediate wax, a paraffin wax, an alpha-olefin wax, or a combination thereof.

12. The method of claim 9 , wherein the outer wax layer comprises an intermediate wax, a paraffin wax, an alpha-olefin wax, or a combination thereof

13. The method of claim 9 , wherein the urea is about 43% N on a weight basis, the thermoset polymer is about 1.8% on a weight basis, the wax layer is about 0.3% on a weight basis, the layer of elemental sulfur is about 3.8% on a weight basis and the outer wax layer is about 0.5% on a weight basis.

14. The method of claim 9 , wherein the urea is about 43% N on a weight basis, the thermoset polymer is about 2.5% on a weight basis, the wax layer is about 0.3% on a weight basis, the layer of elemental sulfur is about 2.2% on a weight basis and the outer wax layer is about 0.5% on a weight basis.

15. A controlled release fertilizer composition, comprising:

a core comprising one or more plant nutrient materials;

a thermoset polymer layer coating the core, wherein the thermoset polymer layer is formed from precursor compounds comprising polymeric MDI, DEG and TEA;

a sulfur layer overlying the polymer layer;

an intermediate wax layer between the polymer layer and the sulfur layer, wherein the intermediate layer comprises an alpha olefin that functions as a lubricant when applying the sulfur layer; and

optionally an outer, water-insoluble layer.