Winter wheat responses to enhanced efficiency granular nitrogen fertilizer in the Canadian Prairies

Optimizing the timing of nitrogen (N) enhanced efficiency fertilizers (EEFs) may maximize winter wheat (Triticum aestivum L.) grain yield, protein content, and N-use efficiency (NUE). From 2013 to 2018, experiments were conducted at two irrigated and six rain-fed sites across the Canadian Prairies (24 site-years) to evaluate winter wheat responses to N source and timing/placement effects of EEFs. Nitrogen sources included untreated urea, nitrification inhibitor nitrapyrin treated urea, urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) plus nitrification inhibitor dicyandiamide (DCD)-treated urea (NBPT + DCD), and polymer-coated urea (PCU). The N sources were all side-banded at planting, 30% side-banded at planting plus 70% broadcast in-crop late-fall (averaged 38 days after planting; split-applied late-fall), or 30% side-banded at planting plus 70% broadcast in-crop early-spring (averaged 224 days after planting; split-applied early-spring). Nitrous oxide and methane emissions were measured at one rain-fed site to test whether N source and timing/placement influenced CO2-equivalents (CO2-eq; nitrous oxide + methane). Under irrigation, NBPT + DCD consistently produced the highest yields regardless of timing/placement; however, the 80% of the recommended rate caused suboptimal protein responses (<= 11%) unless split-application of N was adopted. Untreated urea produced the highest net CO2-eq and yield-scaled CO2-eq emissions, with the highest emissions when urea was split-applied early-spring. To optimize winter wheat production and NUE, we conclude that NBPT + DCD all-banded during seeding operations or split-applied early-spring provided similar and often superior results to other sources, including a more typical system of urea side-banded at the time of seeding.