Polymer free and low odor urease inhibitor formulation with improved storage stability on urea

A urease inhibitor formulation (UI) having a viscosity at a shear rate of 100 s−1 determined according to CIPAC method 192 (rotational rheometer) of at most 100 mPas at 10° C. comprising

• (A) 10 to 45 wt.-% of a mixture (A) comprising N-(n-butyl)thiophosphoric acid triamide (NBPT) and N-(n-propyl)thiophosphoric acid triamide (NPPT),
• (B) 0 to 50 wt.-% of N,N-dimethyl lactamide,
• (C) 20 to 85 wt.-% of a solvent selected from the group consisting of a glycol ether, a glycerin ether, and mixtures thereof, and
• (D) 3 to 25 wt.-% of at least one amine selected from the group consisting of
• (D2) an amine containing not more than one amino group and at least three alkoxy- or hydroxy-substituted C2 to C12 alkyl groups R21, wherein at least one of the groups R21 is different to the other groups R21,
• (D3) an amine containing not more than one amino group and at least two alkoxy- or hydroxy-substituted C2 to C12 alkyl groups R22, wherein at least one of the groups R22 bears the alkoxy or hydroxy substituent at a secondary or tertiary carbon atom and wherein at least one of the groups R22 is different to the other group(s) R22,
• (D4) an amine containing at least one saturated or unsaturated C8 to C40 alkyl group R23,
• (D5) a saturated or unsaturated heterocyclic amine which contains at least one oxygen atom as ring atom and which does not contain a further alkoxy group, and
• (D6) an amine selected from the group consisting of methyl-diethanolamine, methyl-diisopropanolamin, tetrahydroxy-propylethylenediamine, trimethylaminoethylethanolamine, N,N,N′, N′-tetramethyl-1,6-hexanediamine, N,N′N″-tris(dimethylaminopropyl)hexahydrotriazine, and 2,2′-dimorpholinyldiethyl ether,
• each based on the total amount of the urease inhibitor formulation (UI), wherein the inhibitor formulation (UI) is polymer free.

A fertilizer composition (1) comprising a urea-containing fertilizer (F1) and mixture (M) comprising

• (A) a mixture (A) comprising at least one (thio)phosphoric acid triamide;
• (B) N, N-dimethyl lactamide;
• and
• (C) a solvent selected from the group consisting of a glycol ether, a glycerin ether, and mixtures thereof, wherein the mixture (M) is polymer free.