Spatial and temporal corn yield variability in the U.S. Corn Belt during the hybrid era

Authors: MARTINEZ, ROBERTO - Oak Ridge Institute For Science And Education (ORISE); Nowatzke, Laurie; KIRCHNER, OLIVIA - Us Forest Service (FS); Todey, Dennis; LICHT, MARK - Iowa State University

Submitted to: Environmental Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2026
Publication Date: 5/12/2026
Citation: Martinez, R.D., Nowatzke, L.W., Kirchner, O., Todey, D.P., Licht, M. 2026. Spatial and temporal corn yield variability in the U.S. Corn Belt during the hybrid era. Environmental Research Communications. https://doi.org/10.1088/2515-7620/ae66cc.
DOI: https://doi.org/10.1088/2515-7620/ae66cc

Interpretive Summary: Drought is well known to reduce yield for all crops, including corn. The impact of drought has varied over time based on changes in corn varieties and how they react to drought and changing crop management throughout the 20th century in the U.S. Midwest. The impact of drought timing during the season also varies in its impact on crop yields. Generally, increased drought/heat during corn reproductive (tasseling) and grain filling part of the growing season have the greatest chance to reduce yield. This study reviews the drought time of year impact on corn yields and the differences in impact across the Corn Belt. The study compares the Standardized Precipitation Index (SPI) and Standardized Precipitation Evaporation Index (SPEI) as possible metrics for identifying drought impacts on yield by performing linear regression analysis of the two precipitation indices with corn yields for different periods of the last 100 years, reflecting different corn hybrid periods for various crop reporting districts of states across the Corn Belt. The study confirmed previous work on drought timing impacts with stress in July being the main contributor in Illinois. But the study also showed some interesting differences across the region in drought impacts during the growing season. This research also shows changes in drought impact on corn yields during the last 90+ years indicating less overall drought impact in more recent corn varieties and reduced inter-annual variability in yields. Better understanding of drought impacts during the year can help producers and agri-business understand potential yield reductions during the growing season and predict potential yield loss.

Technical Abstract: This study examines historical maize production in the U.S. Corn Belt and the impact of weather variability on yields using crop reporting districts (CRDs) in Illinois, Indiana, Iowa, and Nebraska. We used the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), to evaluate the reliability of predicting district-level yields using the national commodity crop productivity index (NCCPI). Corn yield data were sourced from the USDA’s NASS Quick Stats database, covering three periods: 1929–1959 (first hybrid genotypes), 1960–1979 (rise of agrochemicals), and 1980–2022 (advancements in biotechnology and knowledge). We assessed the relationships between annual yield and the NCCPI, SPI, and SPEI through regression analysis. Corn yield showed a significant linear increase with the passage of time across all evaluated periods and CRDs, with an average increase of 113 kg per hectare per year. Some Nebraska districts recorded peaks exceeding 150 kg per hectare per year between 1960 and 1980. Factors influencing corn production have changed over time, and consequently, the NCCPI has become less robust for predicting corn yield since 1960. While corn yields demonstrated greater variability in earlier periods, stability has improved in recent years. The strongest relationship between historic relative yields (RYs) (actual yields divided by predicted yields) and precipitation indices was observed in central Illinois and northwestern Indiana; several CRDs in Nebraska showed weaker relationships. Notably, SPI during July is the most significant factor related to changes in historic RYs, impacting yields in 11 of the 35 CRDs in the central U.S. Corn Belt.