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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.
Martinez et al. (Wed,) studied this question.