STABILIZED UREA-BASED CORE-SHELL FERTILIZER PARTICLES

1 . A core-shell fertilizer particle comprising:

a core comprising urea, a pH buffering agent, and an urease inhibitor; and

a shell comprising urea, wherein the shell covers at least a portion of an outer surface of the core.

2 . The core-shell fertilizer particle of claim 1 , wherein the core comprises 20 wt. % to 80 wt. % urea, based on the total weight of the core.

3 . The core-shell fertilizer particle of claim 1 , wherein the shell comprises 50 wt. % to 100 wt. % urea, based on the total weight of the shell.

4 . The core-shell fertilizer particle of claim 1 , wherein the core comprises 15 wt. % to 80 wt. % of the pH buffering agent based on the total weight of the core.

5 . The core-shell fertilizer particle of claim 1 , wherein the pH buffering agent is CaCO 3 , Na 2 CO 3 , K 2 CO 3 , MgO, KH 2 PO 4 , NaHCO 3 , or MgCO 3 , or any combination thereof.

6 . The core-shell fertilizer particle of claim 1 , wherein the urease inhibitor comprises a thiophosphoric triamide derivative.

7 . The core-shell fertilizer particle of claim 1 , wherein the core comprises 0.1 wt. % to 5 wt. % of the urease inhibitor, based on the total weight of the core.

8 . The core-shell fertilizer particle of claim 1 , wherein the core further comprises 0.1 wt. % to 7 wt. % of water, based on the total weight of the core.

9 . The core-shell fertilizer particle of claim 1 , wherein the core further comprises a polymer thickener and/or a filler.

10 . The core-shell fertilizer particle of claim 9 , wherein the polymer thickener comprises hydroxypropyl methylcellulose (HPMC), carboxymethyl cellulose, polyethylene glycol (PEG), guar gum, locust bean gum, xanthan gum, a natural gum, lignosulfonate, or hydroxyethylcellulose or any combination thereof.

11 . The core-shell fertilizer particle of claim 9 , wherein the core comprises 0.1 wt. % to 5 wt. % of the polymer thickener, based on the total weight of the core.

12 . The core-shell fertilizer particle of claim 1 , wherein the core further comprises a nitrification inhibitor.

13 . The core-shell fertilizer particle of claim 12 , wherein the nitrification inhibitor comprises dicyandiamide (DCD).

14 . The core-shell fertilizer particle of claim 12 , wherein the core comprises 5 wt. % to 35 wt. % of the nitrification inhibitor, based on the total weight of the core.

15 . The core-shell fertilizer particle of claim 1 , wherein 98 wt. % or higher of the core, based on the total weight of the core, is comprised in urea, CaCO 3 , one or more urease inhibitor, water, and optionally a nitrification inhibitor and/or a polymer thickener.

16 . The core-shell fertilizer particle of claim 1 , wherein:

the core comprises, based on the total weight of the core:

45 wt. % to 60 wt. % or 65 wt. % to 75 wt. % of urea;

20 wt. % to 60 wt. %, preferably 20 wt. % to 45 wt. %, of CaCO 3 ;

1 wt. % to 3 wt. % of the urease inhibitor, wherein the urease inhibitor is N-(n-butyl) thiophosphoric triamide (NBPT);

0.1 wt. % to 3 wt. % of water; and

the shell comprises, based on the total weight of the shell:

85 wt. % to 100 wt. % urea.

17 . The core-shell fertilizer particle of claim 16 , wherein the core further comprises

0 . 5 wt. % to 3 wt. % of hydroxypropyl methylcellulose (HPMC), based on the total weight of the core.

18 . The core-shell fertilizer particle of claim 16 , wherein the core further comprises 20 wt. % to 25 wt. % of dicyandiamide (DCD), based on the total weight of the core.

19 . The core-shell fertilizer particle of claim 1 , wherein the shell does not include CaCO 3 or a urease inhibitor, or both.

20 . The core-shell fertilizer particle of claim 1 , comprised in a fertilizer blend or a compounded fertilizer.