Over the past five decades, corn grain yields in Ohio Corn Performance Tests (Medeiros, et al., 2024) and the state average of on-farm yields (United States Department of Agriculture, National Agriculture Statistics Service, n.d.) have increased at 2.1 and 1.8 bushels-per-acre per year, respectively. A practical question for Ohio farmers is, “How does the observed yield increase impact corn nitrogen rates?” This factsheet summarizes corn yield trends and the agronomically optimal nitrogen rate (AONR) rate, defined as the nitrogen rate that maximizes corn yield and nitrogen-use efficiency using Ohio nitrogen response trials conducted between 1976 and 2021 to better understand the role of nitrogen fertilizer in explaining corn yield increases.
Nitrogen (N) input to corn is critical to optimize yields. Over-application or under-application of N has implications on farm profitability and environmental quality. From the 1970s until 2005, Ohio N recommendations were based on a yield-goal approach, where 1.21 pounds of N per anticipated/desired bushels of corn grain (with an adjustment for the previous crop) was recommended. In 2006, Ohio and other Midwest states adopted the Maximum Return to Nitrogen (MRTN) approach to N rates. The MRTN approach considers corn’s response to N amendments, fertilizer cost, and the market price of corn to determine the N rate that will maximize the return on nitrogen investment (LaBarge & Rakkar, 2025).
A recent study was conducted to better understand corn yield trends based on the optimal nitrogen rate required to maximize yield and nitrogen-use efficiency in Ohio (Fulford, et al., 2025). The study summarized data from 431 N trials conducted over 45 years across 31 counties in Ohio (Table 1). Trial sites were on-farm (20%) and at experiment stations (80%). Fulford, et al. (2025) also looked at genetic impacts on yield by dividing the dataset into two eras:
- pre-transgenic era (1976–1995)
- transgenic era (1996–2021)
| Year | Number of Trials | Previous Crop |
| 1976–1995 | 83 | corn (61); soybean (7); unknown (15) |
| 1996–2021 | 348 | corn (79); soybean (269) |
The Fulford, et al. (2025) study had a number of key findings:
- N rate required to maximize corn yield did not change significantly over the past 45 years, but separating data by eras showed an increase of 3.2 pounds of N per acre per year from 1976–1995 and 1.07 pounds of N per acre per year from 1996–2021 (Fig. 1a and 1b).
- On average, the corn grain yield at an optimal N rate increased from 132 bushels per acre in 1976 to 200 bushels per acre in 2021, an increase of 52%. Looking at different eras separately, the corn yield at an optimal N rate tended to decrease from 1976 to 1995 but showed an increase from 1996–2021 (Fig. 1c and 1d).
- The crop in rotation with corn can influence the yield outcomes and N requirements. In the Fulford, et al. (2025) study, the yields increased whether corn followed corn or soybean in the rotation. The nitrogen rate that maximized yield followed a different pattern. When corn followed corn, the same 222 pounds of N per acre maximized yield across all years. When corn followed soybeans, the N rate to maximize yield increased by 0.85 pounds of N per acre per year.
Corn grain yield increased over 45 years with and without fertilizer (zero N check plots). Yields increased by 1.2 bushels per acre per year when fertilizer was applied. The zero check plots without N fertilizer had a yield increase of 0.5 bushels per acre per year (Fig.2). The similar trendline for yields with and without fertilizer indicate that yield increases are not solely due to N fertilizer but also include breeding advancements and improved agronomic practices. - Grain produced per unit of N input increased by 1.2 times from 1976 to 2021.
Overall, corn grain yield in Ohio has increased substantially over the past 45 years. With regards to the optimum N rate to maximize yield, it has not changed significantly from 1976 to 2021. Results indicated that corn is better at utilizing N per unit of input, potentially due to the improved nitrogen-use efficiency of new hybrids. Medeiros, et al. (2024) also observed similar trends where nutrient input declined from 1972 to 2021, but corn yields increased, potentially due to agronomic improvements such as increased seed rates, improved seedling emergence, and plant stand counts.
Farmers selecting nitrogen rates want to keep in mind the key findings of this study. Newer hybrids use N more efficiently as demonstrated by increased yields whether N is coming from soil mineralization or commercial fertilizer. The N rate needed to optimize yield has increased, but only at a rate of 1 pound per year, while yields have increased 1.2 bushels per year in the study trials. The MRTN tool recommended for Ohio producers uses up-to-date data to calculate yield response and identify economic return to each added unit of N.
References
Fulford, A. M., LaBarge, G., Lindsey, A., Watters, H., Ortez, O., & Culman, S. W. (2025). Historical trends in the nitrogen requirement of corn over 45 years in Ohio. Agronomy Journal, 117(2), e70049.
doi.org/10.1002/agj2.70049
LaBarge, G. & Rakkar, M. (2025). Corn N recommendations: Maximum return to N calculator updated [website]. Ohio State University Extension.
agcrops.osu.edu/newsletter/corn-newsletter/2025-13/corn-n-recommendations-maximum-return-n-calculator-updated
Medeiros, J. C., Zavala, J., Shahrokhi, M., Minyo, R., Geyer, A., Lindsey, A., Thomison, P., & Ortez, O. (2025). An overview of the Ohio corn performance test: Trends over 50 years. Agronomy Journal, 117(1), e221727
doi.org/10.1002/agj2.21727
United States Department of Agriculture, National Agriculture Statistics Service. (n.d.). Quick stats [Website].
quickstats.nass.usda.gov