Can We Increase Spring Wheat (Triticum aestivum L.) Grain and Protein Yields with Urease and Nitrification Inhibitors?.

Urease and nitrification inhibitors have the potential to reduce nitrogen (N) losses from urea-fertilized soils. A 3-year field study (2014-2016) was conducted at Glyndon, MN under rainfed spring wheat (Triticum aestivum L.) to assess the impact of urease and nitrification inhibitors on N losses [ammonia (NH₃) volatilization, nitrous oxide (N₂O) emissions], grain and protein yields. Treatments consisted of three N fertilizer sources [untreated urea (U), urea treated with nitrification inhibitor alone (NI), urea treated with both urease and nitrification inhibitors (DI)] each applied at two different N rates (146 and 168 kg N ha^-1) along with the control (no N). Compared to U, DI significantly reduced NH₃ volatilization by 26% and 34% and N₂O emissions by 50% and 43% in 2014 and 2015, respectively. The NI significantly reduced N₂O emissions over U by 53% in 2015 but no effect was observed in 2014. The NH₃ loss was increased by 48% with NI compared to DI in 2015. Higher N₂O fluxes were observed during optimum soil conditions (35-60% WFPS, temperatures>10-12°C, and high soil NO₃^- contents). The grain and protein yields were similar among U, NI, and DI treatments. These results suggest that the combined application of both urease and nitrification inhibitors could be an effective means to reduce all possible N losses from urea-fertilized soils, whilst maintaining economic returns in a rainfed spring wheat system. The final presentation will also include results from the third year (2016).