Historical Corn Grain Yields In The U.S.

• Corn grain yields in the U.S. have steadily increased since the late 1930’s.
• Only two major shifts in U.S. corn yield trends have occurred since statistics were first published in 1866.
• Year-to-year departures from trend yield are influenced primarily by year-to-year variability in growing conditions.

Historical grain yields offer us a glimpse of yields yet to come, although like the stock markets, past performance is no guarantee of the future. The historical yield data for corn in the U.S. illustrate the positive impact of improved crop genetics and crop production technologies.

American farmers grew open-pollinated corn varieties until the rapid adoption of hybrid corn began in the late 1930’s. From 1866, the first year USDA began to publish corn yield estimates, through about 1936, yields of open-pollinated corn varieties in the U.S. were fairly stagnant and only averaged about 26 bu/ac (1.6 MT/ha) throughout that 70-year period. Amazingly, the historical data indicate there was no appreciable change in productivity during that entire time period (Fig. 1), even though farmers’ seed-saving practices represented a form of plant breeding that one would have expected would result in small increases in yield over 70 years.

Rapid adoption of double-cross hybrid corn by American growers began in the late 1930’s, in the waning years of the Dust Bowl and Great Depression. Within a very few years, the national yield statistics indicated that the first “miracle” of corn grain yield improvement had occurred. The annual rate of yield improvement, which heretofore had been about zero, increased to about 0.8 bushels per acre per year from about 1937 through about 1955 (Fig. 1). This dramatic improvement in yield potential must have seemed like a miracle to American farmers.

Trend Line Trivia: Historical trend lines can be a useful way to visualize changes over time. The historical trend yield lines shown in Fig. 1 are technically linear regression lines and represent the best “fit” method for describing the changes in U.S. corn yields over time. The equation associated with the trend line that begins in the 1950s can be used to predict U.S. corn yield for the current cropping year under “normal” growing conditions. Year-to-year departures (changes) from the trend line are caused primarily by year-to-year variability in growing conditions. However, significant changes in the trend line itself (i.e., the slope of the line) are usually caused by significant changes in the adoption of farming technologies (e.g, hybrids, pest control, soil management, mechanization, precision ag. technologies).

The second “miracle” of corn grain yield improvement began in the mid-1950’s in response to continued improvements in genetic yield potential and stress tolerance plus increased adoption of N fertilizer, chemical pesticides, and agricultural mechanization (Fig. 1). The annual rate of corn yield improvement more than doubled to about 1.9 bushels per acre per year and has continued at that steady rate ever since, sustained primarily by continued improvements in genetics and crop production technologies (Fig. 1).

Some speculate that a third “miracle” of corn grain yield improvement is “on the horizon”, in part due to the advent and adoption of transgenic hybrid traits (insect resistance, herbicide resistance) beginning in the mid-1990’s. However, the USDA-NASS yield data show little to no evidence that yield trends of the past 25 years have deviated from the long-term 1.9 bushels per acre per year trend line (Fig. 1). These data reinforce the fact that currently available transgenic hybrid traits do not literally increase genetic yield potential above and beyond “normal” genetic improvements in corn hybrids. Rather, these traits simply protect the inherent yield potential of modern hybrids while potentially reducing farmers’ reliance on chemical pesticides. A true third “miracle” of corn yield improvement remains “on the horizon”.

Annual corn yields continually fluctuate above and below the historical trend line (Fig. 2), primarily in response to variability in growing conditions year to year (weather, pests). The Great Drought of 2012 certainly resulted in dramatic and historic reductions in corn grain yield relative to trend yield (-22%), but the greatest negative departure from trend yield actually occurred more than 100 years earlier during the Great Drought of 1901 (-30%). Conversely, the greatest single positive departure from trend yield occurred in 1906 when the corn crop that year yielded 23% higher than expected trend yield. The magnitude and range of annual departures from trend yield since the mid-1950’s reinforce the evidence from Fig. 1 that the advent and adoption of transgenic hybrid traits beginning in the mid-1990’s has not resulted in yields unusually higher than the long-term yield trend.

Bottom Line

The GOOD NEWS is that corn grain yields in the U.S. have been steadily increasing since the 1950’s at almost 2 bushels per acre per year. The SOBERING NEWS is that, in order to support the ever-burgeoning world population in the years to come, a third “miracle” in the annual rate of corn yield improvement will be required.

Related Reading

Irwin, Scott and Darrel Good. 2012. The Historic Pattern of U.S Corn Yields, Any Implications for 2012? farmdoc daily (2):21, Department of Agricultural and Consumer Economics, University of Illinois at Urbana-Champaign. https://farmdocdaily.illinois.edu/2012/02/the-historic-pattern-of-us-cor-1.html [URL accessed Apr 2020].

Kucharik, Christopher and Navin Ramankutty. 2005. Trends and Variability in U.S. Corn Yields Over the Twentieth Century. Earth Interactions (American Meteorological Society) 9:1-9. https://doi.org/10.1175/EI098.1 [URL accessed Apr 2020].

Schnitkey, Gary. 2019. The Geography of High Corn Yields. farmdoc daily (9):2, Department of Agricultural and Consumer Economics, University of Illinois at Urbana-Champaign. https://farmdocdaily.illinois.edu/2019/01/the-geography-of-high-corn-yields.html [URL accessed Apr 2020].

USDA-NASS. 2020. Quick Stats. United States Dept. of Agr – Nat’l Ag. Statistics Service, Washington, D.C. URL: https://quickstats.nass.usda.gov [URL accessed Apr 2020].

Ward, Robert De C. 1901. Some Economic Aspects of the Heat and Drought of July, 1901, in the United States. Bull. Amer. Geog. Soc. 33(4):338-347. DOI: 10.2307/198424. https://www.jstor.org/stable/pdf/198424.pdf [URL accessed Apr 2020].