Is an economically optimal corn nitrogen rate also environmentally optimal

Authors: BANDURA, CHRISTOPHER - University Of Wisconsin; Laboski, Carrie; CAMBERATO, JAMES - Retired Non ARS Employee; CARTER, PAUL - Retired Non ARS Employee; CLARK, JASON - South Dakota State University; FERGUSON, RICHARD - University Of Nebraska; FERNANDEZ, FABIAN - University Of Minnesota; FRANZEN, DAVID - North Dakota State University; KITCHEN, NEWELL - Retired ARS Employee; NAFZINGER, EMERSON - University Of Illinois; Ransom, Curtis; SAWYER, JOHN - Retired Non ARS Employee; SHANAHAN, JOHN - Agoro Carbon Alliance

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2025
Publication Date: 7/16/2025
Citation: Bandura, C.J., Laboski, C.A., Camberato, J.J., Carter, P.R., Clark, J.D., Ferguson, R.B., Fernandez, F.G., Franzen, D.W., Kitchen, N.R., Nafzinger, E.D., Ransom, C.J., Sawyer, J.E., Shanahan, J.F. 2025. Is an economically optimal corn nitrogen rate also environmentally optimal. Soil Science Society of America Journal. 89. Article e70105. https://doi.org/10.1002/saj2.70105.
DOI: https://doi.org/10.1002/saj2.70105

Interpretive Summary: In corn production farmers tend to overapply nitrogen fertilizer to ensure yields are maximized. This practice results in more nitrogen being lost to the environment thereby accelerating the degradation of the atmosphere and waterways. Currently many states in the US Corn Belt suggest applying nitrogen at rates that maximize profit (i.e., the economically optimal nitrogen rate, EONR) and not yield. However, there are still concerns that this target N rate may have environmental consequences. The objective of this investigation was to evaluate the effect of N fertilizer application rate and timing on crop N use and loss relative to EONR. Research was conducted on 49 nitrogen response trials across eight states in the US Midwest from 2014 to 2016. Nitrogen was either applied all at the time of planting or split applied between planting and in season. Nitrogen rates varied from no nitrogen up to an excessive amount of nitrogen (315 kg N ha^1). The amount of nitrogen taken up by plants and soil nitrate remaining in the soil were measured from each plot. Key findings showed that nitrogen application timing determined when nitrogen would be lost to the environment with split application resulting in more nitrate remaining in the soil after harvest. Appling nitrogen at rates close to EONR did not result in increased residual soil nitrate compared to lower nitrogen rates. However, nitrogen rates that exceeded EONR substantially increased the amount of residual soil nitrate. These findings suggest that using EONR as the target nitrogen rate is both profitable and minimizes environmental concerns.

Technical Abstract: The economically optimal nitrogen rate (EONR), while an accepted standard as the “right rate” for corn (Zea mays L.) fertilization, does not directly account for environmental impacts. This study evaluated the effects of nitrogen (N) fertilizer application rate and timing on crop N use and N loss potential, using residual soil nitrate-N (RSN; 0–0.9 m depth), relative to EONR. The evaluation was conducted using 49 N response trials from eight US Midwest states from 2014 to 2016. Nitrogen rates were applied as ammonium-nitrate, either all at planting or split between at planting (45 kg N ha-1) and the remainder at ~V9 growth stage. At EONR, RSN was 42 kg N ha-1 for at-plant applications and 62 kg N ha-1 for split applications. However, unaccounted for N at the end of the growing season was greater for at-plant (46 kg N ha-1) compared to split applications (21 kg N ha-1). This suggests a higher susceptibility of N loss during the early season for at-planting applications, and after the season for split applications. Differences in RSN at the EONR between N timings were not explained by differences in total aboveground N uptake at R6. Residual soil nitrate did not substantially increase until N application rates exceeded the EONR by 30 kg N ha-1. These findings support using EONR, at a N:corn price ratio of 5.6, as a N application sustainability standard that balances profitability and environmental concerns.