DOI: 10.5061/dryad.3bk3j9kxg
title: Historical trends in the nitrogen requirement of corn over 45 years in Ohio

description: The average annual corn (Zea mays L.) grain yield in Ohio has increased
 since the 1970s, yet the respective roles of corn hybrids and optimal
 nitrogen (N) fertilization in contributing to this historical trend remain
 unclear. This study evaluated trends in the agronomically optimal nitrogen
 rate (AONR) and corn grain yield at agronomically optimal nitrogen rate
 (YAONR) when corn followed corn (CC) or soybean [Glycine max (L.) Merr.]
 (SC) in the crop rotation within two eras of corn hybrid development. The
 two eras were associated with different technological development phases,
 including 1976–1995 (pre-transgenic era) and 1996–2021 (transgenic era). A
 total of 431 rainfed corn fertilizer N rate response trials were conducted
 in 31 Ohio counties over 45 years. From 1976 to 2021, AONR did not
 significantly increase, while YAONR increased by 96.1 kg per ha per year,
 a 52% increase over 45 years. Unfertilized (0 kg N per ha) corn yield
 gains were similar to annual yield gain at AONR, and the agronomic
 nitrogen-use efficiency (ANUE) greatly improved over 45 years, with an
 additional 4.6 kg of grain per kg of N for corn grown in 2021 compared to
 1976. Overall, our study demonstrated that historical yield gains were
 largely due to improved corn hybrid ANUE and management rather than
 changes in N fertilizer requirements.
description: # Historical trends in the nitrogen requirement of corn over 45 years in
 Ohio Dataset DOI: [10.5061/dryad.3bk3j9kxg](10.5061/dryad.3bk3j9kxg) ##
 Description of the data and file structure Ohio State University Corn
 Nitrogen Rate Data (1976-2021) Ohio corn N rate dataset published in
 Fulford et al., 2025:
 [https://doi.org/10.1002/agj2.70049](https://doi.org/10.1002/agj2.70049)
 Dataset contains two data files: 1) Experimental_Design: Data related to
 the experimental design of each trial. One observation per trial. (431
 observations x 18 variables) 2) Crop_Data: Crop N fertilizer applied and
 total corn grain yields. One observation per plot or per N rate. (5,778
 observations x 7 variables) Periods (.) in datasheets indicate missing
 information. Questions about these data or the use of these data should be
 directed to Steve Culman:
 [steve.culman@oregonstate.edu](mailto:steve.culman@oregonstate.edu) ###
 Files and variables **Description:** Two data files: Experimental_Design
 and Crop_Data ##### Variables | Data File | Variable | Explanation | Unit
 | Variable type | Number of Unique Entries | | :------------------- |
 :-------------------- |
 :--------------------------------------------------------------------------------------------- | :------- | :------------ | :----------------------- | | Experimental\_Design | Trial | Unique numeric identifier assigned to each site-year | . | Discrete | 431 | |   | Year | Year trial was conducted | . | Date | 35 | |   | County | Ohio county where trial was conducted | . | Discrete | 31 | |   | Trt\_vs\_Plot | Data reported as averaged values at the treatment (N rate) level or raw data at the plot level | . | Discrete | 2 | |   | Number\_N\_Rates | Total number of nitrogen rates in trial | . | Numeric | 6 | |   | Number\_Reps | Total number of replications in trial, if data reported at the plot level | . | Numeric | 3 | |   | Previous\_Cash\_Crop | Last cash crop grown before trial was conducted | . | Discrete | 5 | |   | Previous\_Cover\_Crop | Cover crop grown immediately before planting corn | . | Discrete | 8 | |   | Tillage\_Type | Tillage type | . | Discrete | 4 | |   | Planting\_Date | Year-Month-Day of planting corn | . | Date | 208 | |   | Hybrid | Corn hybid number | . | Discrete | 101 | |   | Relative\_Maturity | Corn hybrid days to maturity | Day | Discrete | 7 | |   | N\_Source\_PP | Type of N fertilizer applied before planting | . | Discrete | 6 | |   | N\_Source\_Plant | Type of N fertilizer applied at planting | . | Discrete | 5 | |   | N\_Source\_SD | Type of N fertilizer applied at sidedress | . | Discrete | 4 | |   | N\_manipulation | Time when N rate treatments were manipulated | . | Discrete | 2 | |   | OnFarm\_vs\_OnStation | Trial conducted on private farm (On-Farm) or public research farm (On-Station)? | . | Discrete | 2 | |   | Manure\_History | History of manure application and type of animal manure if known. | . | Discrete | 6 | | Crop\_Data | Trial | Unique numeric identifier assigned to each site-year | . | Discrete | 431 | |   | Rep | Replicate or block number | . | Discrete | 5 | |   | PrePlant\_N | N applied at preplant | kg N/ ha | Numeric | 25 | |   | AtPlant\_N | N applied at planting | kg N/ ha | Numeric | 32 | |   | Sidedress\_N | N applied at sidedress | kg N/ ha | Numeric | 62 | |   | Total\_N | Total N applied over growing season, use this variable for modeling N rate | kg N/ ha | Numeric | 118 | |   | Yield | Corn grain N yield, adjusted to 15.5% moisture, megagrams per hectare | Mg/ ha | Numeric | . |