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Nitrogen rate to optimize corn yield: Insights from 1976-2021 dataset

Growing Corn

Corn yield has increased by about threefold across the US from 1950s to 2000s. Therefore, a practical question for farmers is, “How does the observed yield increase impact corn nitrogen rates?” To answer this question, a recent factsheet summarized the trends of corn yield, optimal nitrogen rate to maximize yield, and nitrogen use efficiency of corn based on Fulford et al (2025) study (Rakkar and LaBarge, 2025). The study included data from 431 N trials conducted over 45 years across 31 counties in Ohio.

Nitrogen Rate Trials

Below are some key takeaways:

Did corn grain yield increase from 1976 to 2021 in Ohio?

Yes, corn grain yield increased from 1976 to 2021 in Ohio. The yield increased by 1.2 bu/ac/yr with N fertilizer and by 0.5 bu/ac/yr without N fertilizer (Fig. 1).

Fig.1 Trendline of corn grain yields over 45 years with (yellow dots) and without (blue dots) nitrogen fertilizer (adapted from Fulford et al. 2025).

Did the nitrogen rate needed to maximize corn yield (AONR) increase in the past 45 years?

No, AONR did not change significantly.

Did corn yield at optimal nitrogen rate (YAONR) increase from 1976 to 2021?

Yes, YAONR increased by 52%.

What do trends of corn yield, AONR, and YAONR reflect?

The trends reflect that corn is better at utilizing N per unit of input, potentially due to the improved nitrogen-use efficiency of new hybrids. Grain produced per unit of N input has increased by 1.2 times from 1976 to 2021.

What is the implication of these research findings to current N recommendations in Ohio?

The Ohio State University utilizes Maximum Return to Nitrogen (MRTN) for corn N recommendations. The MRTN approach considers corn’s response to N amendments, fertilizer cost, and the market price of corn to determine the N rate. The MRTN tool uses up-to-date data to account for improved nitrogen use efficiency of corn.  

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

Rakkar, M. & LaBarge, G. (2025). Trends of Corn Yield, Optimal Nitrogen Rate, and Nitrogen Use Efficiency: 1976–2021. Ohioline. ANR-0200. https://ohioline.osu.edu/factsheet/anr-0200

 

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C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.