Is the Trend Rate of Growth in the U.S. Average Corn Yield Slowing?

Projecting the size of the U.S. corn crop depends on two components—harvested acreage and yield per acre. The USDA Prospective Planting report released near the end of March provides a starting point in making this important projection. The report showed that U.S. farmers intend to plant 90 million acres of corn during the 2024 planting season. Combined with an estimate of the difference between planted and harvested acreage, this can be used to project harvested acreage. Yield is then the only remaining component needed to project crop size. Given the difficulty of forecasting summer weather conditions so far in advance, a simple “trend” projection is typically used at this point in the season. Despite the seeming simplicity of making a trend projection, there is always debate about the best way of going about it. Currently, there is more than the usual amount of debate because U.S. average corn yields have moved in a fairly narrow range for more than a decade. Some argue that the growth of trend corn yield in the U.S. has slowed considerably since 2013 (Boussios, 2024), while others caution about projecting trend yields from a small sample of years (farmdoc daily, April 16, 2024). The purpose of this article is to use a crop weather model of the U.S. average yield of corn to formally test whether the trend rate of growth in the U.S. average corn yield has slowed in recent years.