Effects of nitrogen rate and timing applied as anhydrous ammonia on corn production and profitability in Central Illinois

Abstract

Nitrogen (N) application timing is a critical decision for Illinois corn ( Zea mays L.) producers to balance operational efficiency, economic return, and environmental stewardship. Potential N loss before crop uptake raises concern about environmental and economic consequences of fall application. We compared agronomic and economic responses to N rates applied as anhydrous ammonia in the fall and spring at 19 Central Illinois sites from 2013 to 2020. Economic optimum nitrogen rates (EONRs) across sites were 195 kg N ha ⁻¹ for fall N and 179 kg N ha ⁻¹ for spring N. Yield response to N rate was similar between timings at 16 of 19 sites; at the remaining three sites, spring N performed better than fall, as indicated by increased yield at a similar EONR or lower EONR at a similar yield, or both. Yield at the economic optimum nitrogen rate (Y _EONR ) averaged 14.4 Mg ha ⁻¹ for fall N and 14.5 Mg ha ⁻¹ for spring N. Net return to nitrogen (RTN) at the economic optimum nitrogen rate (RTN _EONR ) averaged $1054 ha ⁻¹ for fall N and $1095 ha ⁻¹ for spring N; of the $41 ha ⁻¹ advantage to spring N, $14 was from lower N rate and $27 from higher yield. Fall N increased EONR compared to spring ( p  = 0.014); Y _EONR ( p  = 0.407) and RTN _EONR ( p  = 0.126) did not differ between timings. Yield and RTN using Illinois N rate guidelines (yield at the appropriate Illinois guideline nitrogen rate [Y _MRTN ] and (net) return to nitrogen at the appropriate Illinois guideline nitrogen rate [RTN _MRTN ], respectively) did not differ between timings ( p  > 0.1). While site‐specific responses varied, spring application had a lower mean EONR, with Y _EONR and RTN _EONR similar between timings.