Wheat Production, Nitrogen Transformation, and Nitrogen Losses as Affected by Nitrification and Double Inhibitors

Abstract

Core Ideas The environmental and agronomic benefits of amending urea with inhibitors was evaluated. Double inhibitor significantly reduced all three major N losses compared with urea. Nitrification inhibitor did not reduce NH3 volatilization. Higher N2O fluxes were observed at 35 to 60% WFPS, soil temperature >10°C, and NO3− contents >5 mg kg−1 dry soil. Nitrification inhibitor/double inhibitors maintained spring wheat grain and protein yields. Enhanced efficiency fertilizers have the potential to reduce N losses from urea (U)‐fertilized soils. A field study was conducted during 2015 and 2016 at Glyndon, MN, under rainfed spring wheat (Triticum aestivum L.) to assess the effectiveness of U with/without nitrification inhibitor (NI) or both urease and nitrification inhibitors (DI) to reduce N losses and improve crop yields. Treatments consisted of three N sources (U, NI, and DI) applied at two N rates (146 and 168 kg N ha−1) along with the control. In 2015, DI significantly reduced ammonia (NH3) volatilization by 34% and nitrous oxide (N2O) emissions by 43% as compared with U (7.78 kg NH3–N ha−1, 2.24 kg N2O‐N ha−1). Similarly, NI (9.85 kg NH3–N ha−1, 1.05 kg N2O‐N ha−1) significantly reduced N2O emissions by 53%, but had similar NH3 loss to that of U. The DI significantly reduced NH3 loss by 48% compared with NI. Higher N2O fluxes were observed when WFPS (water‐filled pore space) lies between 35 and 60%, soil temperature >10 to 12°C, and soil NO3− contents >5 mg kg−1. Urea with NI or DI also reduced soil water nitrate (NO3−) concentrations below the rooting zone. 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, while maintaining crop yields in rainfed spring wheat system.