Liquid formulations of urease inhibitors for fertilizers

A liquid fertilizer additive solution comprising:

• a) a urease inhibitor,
• b) a first solvent,
• c) a second solvent, and
• d) a surfactant,
• wherein said first solvent is dimethyl sulfoxide,
• wherein said second solvent is an alkanolamine,
• wherein said urease inhibitor is initially dissolved in said first solvent and said second solvent, and optionally
• e) dyes and colorants, wherein the dyes and colorants provide a visual confirmation that the liquid fertilizer additive solution has been delivered as an even coating to urea,
• wherein said urease inhibitor is N-(n-butyl) thiophosphoric triamide (NBPT), and
• wherein said NBPT is present in the liquid fertilizer additive solution from 30 weight percent to 75 weight percent.