Effect of nitrogen source, placement and timing on the environmental performance of economically optimum nitrogen rates in maize

•At economically optimal nitrogen rates (EONR), N management did not affect yield.•Broadcasting N, particularly as urea, increased the EONR, relative to incorporation.•Application timing did not affect EONR, but in-season applications decreased leaching.•Yield-scaled N losses were never minimized at the EONR.•Mean yield-scaled N loss at the EONR was 4 kg N Mg−1 and N surplus was 28 kg N ha−1. The goal of most fertilizer decision support tools is to help maize farmers estimate the most profitable nitrogen (N) rate for a given fertilizer N/grain price ratio, known as the economically optimum N rate (EONR). While maximizing profitability, to our knowledge the environmental performance of the EONR has not been fully assessed using a process-based model that can jointly predict yield, N uptake, and multiple N loss pathways (leaching, nitrous oxide emissions, volatilization). The objective of this study was to construct a full N budget when the EONR is applied, and to measure how N management influences both grain yield and the environmental performance of the EONR. The DeNitrification and Decomposition model (DNDC) was calibrated and validated using measurements from a long-term N rate trial from Elora, ON, Canada (2009–2016). DNDC was then used to simulate N applications at the EONR when two different N sources (urea and urea ammonium-nitrate), two N placements (broadcast or incorporated) and four N timings (100 % at planting, 100 % at V6, 50 % at planting and 50 % at V13, and 50 % at V6 and 50 % at V13) were used. Depending on N management, mean EONR (2009–2016) was highly variable, ranging from 158 to 185 kg N ha−1 while grain yield was stable across N management choices. The use of urea over urea ammonium-nitrate (UAN), and the decision to broadcast versus incorporate, increased the EONR, yield-scaled N/ losses at the EONR, and N surplus. When applied in-season, N applications modestly reduced leaching N losses at the EONR but did not significantly impact the amount of N applied at the EONR or yield-scaled N losses. In all 16 management combinations, simulated mean (2008–2016) N surplus never exceeded 50 kg N ha−1, and yield-scaled N losses never exceeded 8 kg N Mg−1 grain. In conclusion, the EONR delivers strong environmental performance relative to established benchmarks for N surplus and yield-scaled N losses, while N management decisions such as N source and N placement will still affect in-season N losses and consequently the amount of N applied at the