Nitrification inhibitors and urease inhibitors have been commercially available to farmers for several years. Nitrification inhibitors are intended to minimize losses of nitrate nitrogen (NO3-N) from soil due to leaching and denitrification, by slowing the activity of soil bacteria which convert ammonium nitrogen (NH4-N) to the more easily lost NO3-N. This has the potential to make NH4-N or urea fertilizer sources of N more effective, particularly during late spring and early summer when soil and climatic conditions are usually more favorable for leaching or denitrification of NO3-N. Urease inhibitors slow the activity of the natually occurring urease enzyme which is necessary for changing urea N to NH4-N. This results in less potential volitalization loss of ammonia N (NH3-N) from surface appliations of urea. A nitrogen fertilizer being offered for sale to Kentucky farmers, Super Ureaâ (Super U), a solid, pelleted urea, contains both the nitrification inhibitor DCD (dicyandiamide) and the urease inhibitor, NBPT (N-(nbutyl)thiophosphoric triamide). Claim for use of Super U is to reduce volatilization loss of NH3-N, released as urea breaks down to NH4-N in the soil, and to reduce losses from NO3-N. Potentially, this would improve the efficiency of urea, particularly in topdress applications such as on notill corn, pastures, hayfields, or lawns. Since Super U contains both DCD and NBPT, it sells for a higher price per pound of N than regular urea.
Wells, Kenneth L.; Dollarhide, James E.; and Burkwhat, H. E., "Field Evaluation of Super Urea® for Production of No-Till Corn" (1999). Agronomy Notes. 16.