Ensuring sufficient fertilizer nitrogen (N) for crops while minimizing N losses requires best management practices optimized for climate, crop, soil, and root zone hydrology. In Ontario, pre‐plant N fertilization of corn (Zea mays L.) is common; however, this practice extends the time between application and significant root interception of N by the plant, potentially increasing the risk of N loss through soil nitrous oxide emissions, ammonia (NH3) volatilization, and nitrate leaching. These losses contribute to greenhouse gas emissions, affect air quality (NH3), and are a substantial financial loss. This study compared three N placement methods (broadcast urea [BrUrea], broadcast incorporated urea [BrIncUrea], and injected urea ammonium nitrate [InjUAN]) and the presence or absence of N metabolite inhibitors (urease inhibitor [UI], urease plus nitrification inhibitor [UI+NI]). Fertilizer N was applied immediately before planting (150 kg N ha−1) to all treatments except for the control. Averaged over 3 yr (2015–2017), NH3 losses were reduced by 34% from BrIncUrea, by 42–55% from BrUrea+UI+NI and BrIncUrea+UI+NI, and by 99% from InjUAN relative to BrUrea (21 kg N ha−1). On average, N application increased corn grain yields by 83% relative to the control (6 t ha−1). There were no annual yield differences among N placement methods. It was concluded that incorporation or injection of N in soil and use of urease and nitrification inhibitors reduced NH3 emissions when N fertilizer was applied pre‐plant.

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Core idea 1: Nitrifier denitrification was likely the primary N 2 O pathway under rotation corn (RC) treatments Core idea 2: Nitrous oxide emissions under continuous corn (CC) appeared to be controlled primarily by denitrification Core idea 3: N 2 O emissions were stimulated by early-season rainfall in RC and mid-season rainfall in CC Core Idea 4: The average N 2 O emissions over the 4 year rotation were 54% lower than CC Core idea 5: N 2 O emissions from RC were 16.5% greater than from CC

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