Effectiveness of Urease and Nitrification Inhibitors, Placement and Time of Application on Improving Corn Grain Yields in a Clay Loam Soil.

            Improvement of nitrogen (N) use efficiency in field crops can be linked to mitigating fertilizer N losses through the use of nitrification (NI) and urease inhibitors (UI), as well as fertilizer placement and timing of application.  In 2015 an N source, placement and timing field study was initiated on a corn crop in clay loam soil in Southwestern Ontario.  Fertilizers included; Urea, Urea + UI and Urea UI+NI both broadcast applied and broadcast applied + incorporation; urea-ammonium nitrate (UAN), UAN + UI and UAN UI+NI which was injection applied at planting and the 6-8 leaf stage. Significant precipitation occurred after fertilization at planting and this is a likely source of significant N loss through nitrate leaching. Resulting in the side-dress UAN treatments being significantly greater then broadcast, broadcast incorporated and injection at planting treatments (13.6 vs ~10.0 t ha^-1). The planting treatments that used NI had greater yields than those treatments without. The corn grain yields for injected UAN with UI+NI (11.34 t ha^-1) had 14% greater yields than the injected treatment at planting with no inhibitors (9.9 t ha^-1). Comparing the side-dress treatments the greatest corn grain yields were associated with UAN with UI+NI (13.92 t ha^-1) compared to the treatment with only UI inhibitor (12.2 t ha^-1).