Improved Nitrogen Placement, Timing and Inhibitors Can Reduce N Losses and Increase Corn Yields.

The 4R strategy has been proposed as a best management practice to reduce nitrogen losses from soils especially when precipitation rates, frequency and timing can vary dramatically between growing seasons. We initially compared broadcast versus injected UAN and three inhibitor treatments (control, urease inhibitor or a urease and nitrification inhibitor) on ammonia volatilization, nitrous oxide emissions and corn yields. In the first study, about 50% of broadcast urea was lost from the soil via ammonia volatilization. These ammonia losses were reduced by ~60% when a urease inhibitor was added to urea or when UAN was injected. Ammonia loss was virtually eliminated when UAN with a urease inhibitor was injected. Corn grain yields increased by 5-7% when a urease and nitrification was added with broadcast urea or when UAN was injected. The combination of two N management strategies (injection with urease and nitrification inhibitors) increased yields by 19% compared to broadcast urea application. In the second study, we compared two application times (planting versus sidedress) and 3 application methods (broadcast urea, broadcast and incorporated urea or injected UAN) with/without a urease inhibitor or a combination of urease and nitrification inhibitors on N losses and corn yields. Broadcast and incorporated urea reduced N losses compared to broadcast urea but UAN injection reduced N losses the most of the 3 application methods. Corn grain yields were 15% greater with the sidedress injection of UAN compared to applying broadcast urea at planting.