Increasing longevity of the nitrogen content of soil through improved liquid delivery formulations of urease inhibitors and/or nitrification inhibitors designed to apply to fertilizers, especially urea and manure based fertilizers These delivery formulations provide an environmentally sound and inherently safe solvating system that improves the storage stability of the urease inhibitors by utilizing aprotic solvents, maintain the urease inhibitors and/or nitrification inhibitors in solution to storage temperatures of at least 10° C. and provides improved application to fertilizer of urease and/or nitrification inhibitors. These delivery formulations enable safe storage, transport and subsequent application or blending with urea based or manure based fertilizers that can be applied to soil in either a liquid or granular form to provide improved nitrogen retention in the soil for uptake for plant life.