Enhanced efficiency urea fertilizers and timing effects on N 2 O emissions from spring wheat production in Manitoba

Opportunities exist to reduce nitrous oxide (N 2 O) emissions from nitrogen (N) fertilizers using enhanced efficiency fertilizers (EEFs) and managing application timing. This study examined (1) application timing (fall/spring) and (2) fertilizer N source on N 2 O emissions, yield, and N uptake of Canadian hard red spring wheat ( Triticum aestivum L.) in Southern Manitoba. Fertilizer N sources included granular urea and four EEF products: (1) polymer‐coated urea (environmentally smart nitrogen [ESN]); (2) urea plus nitrification inhibitor (eNtrench); (3) urea plus urease inhibitor (Limus); and (4) urea plus nitrification and urease inhibitor (SuperU). Nitrification‐inhibited products most consistently reduced N 2 O emissions while maintaining productivity. Compared to urea alone, urea + eNtrench was most effective in reducing cumulative N 2 O emissions by 47%–64% at four of six site‐years. SuperU reduced N 2 O emissions by 37%–57% at three of six site‐years. ESN and urea + Limus did not affect emissions in most years. Wheat yield, protein, and N uptake were unaffected by N source in five of six site‐years. Compared to spring, fall application gave greater N 2 O emissions by 33%–67% at three of six site‐years due to spring‐thaw emissions. Fall was inferior to spring application in wetter site years with lower yield, protein, and N uptake. Overall, nitrification‐inhibited products—either alone or with a urease inhibitor—are a promising tool to reduce N 2 O emissions while maintaining wheat productivity in Manitoba. However, given that there were few consistent increases in yield or protein, the additional cost of the inhibitors will be a barrier to adoption. EEF products with nitrification and nitrification/urease inhibitors consistently reduced N 2 O emissions. Controlled release urea and urease‐inhibited urea did not reduce N 2 O emissions. Fall application of urea increased N 2 O emissions in three site‐years compared to spring application. The nitrification inhibitors applied with urea in fall or spring were effective to reduce N 2 O emissions. Overall, fall application decreased yield, grain protein, and N uptake in relatively wet years.