Controlled-release fertilizer compositions

1. A controlled-release fertilizer composition comprising:

a plurality of coated fertilizer particles each consisting of a granule, four or more polyurethane coating layers, and optionally a wax coating layer, wherein the four or more polyurethane coating layers substantially encapsulate the granule and the innermost layer of the four or more polyurethane coating layers contacts the granule; and

wherein the four or more polyurethane coating layers are formed from the reaction product of a polyol composition and an isocyanate curing agent;

wherein the polyol composition comprises a hydrophobic cardanol-based polyol and an aromatic amine-based polyol;

wherein the granule consists of urea.

2. The controlled-release fertilizer composition according to claim 1 , wherein the coated fertilizer particles comprise about 1% to about 5%, by weight, of the four or more polyurethane coating layers.

3. The controlled-release fertilizer composition according to claim 1 , wherein the coated fertilizer particles comprise the wax coating layer surrounding the four or more polyurethane coating layers.

4. The controlled-release fertilizer composition according to claim 1 , wherein the isocyanate curing agent comprises one or more of a polymeric isocyanate, an aromatic isocyanate, and 4,4′-methylene diphenyl isocyanate.

5. The controlled-release fertilizer composition according to claim 1 , wherein the ratio of the polyol composition to the isocyanate curing agent is about 1:4 to about 1:1.

6. The controlled-release fertilizer composition according to claim 1 , wherein the four or more polyurethane coating layers comprise a catalyst selected from one of an amine-based catalyst or a metal salt catalyst.

7. The controlled-release fertilizer composition according to claim 1 , wherein the polyol composition further comprises a polyether polyol.

8. The controlled-release fertilizer composition according to claim 7 wherein the polyether polyol comprises one or more of an ethylene oxide polyol and a propylene oxide polyol.

9. The controlled-release fertilizer composition according to claim 7 , wherein the polyol composition comprises about 1% to about 99%, by weight, of the cardanol-based polyol.

10. The controlled-release fertilizer composition according to claim 1 has a nutrient release profile of about 90 days or greater.

11. A method of fertilizing comprising applying the controlled-release fertilizer composition according to claim 1 to soil.

12. A method of making a controlled-release fertilizer composition comprising:

coating granules consisting of urea with a polyol composition; and

applying an isocyanate curing agent to the polyol composition to form an initial polyurethane coating layer substantially encapsulating each granule, the initial polyurethane coating layer contacting the granule;

forming three or more additional polyurethane coating layers overlying the initial polyurethane coating layer; and

wherein the polyol composition is miscible with the isocyanate curing agent;

wherein the polyol composition comprises a hydrophobic cardanol-based polyol and an aromatic amine-based polyol; and

wherein the controlled-release fertilizer composition consists of the granule, four or more polyurethane coating layers, and optionally a wax coating.

13. The method according to claim 12 , wherein the polyol composition and the isocyanate curing agent are included in about a 1:4 ratio to an about a 1:1 ratio.

14. The method according to claim 12 , wherein the polyol composition further comprises a polyether polyol.

15. The method according to claim 12 , wherein the polyol composition comprises about 1% to about 99%, by weight, of the cardanol-based polyol.