Since 1945, U.S. national average corn yield has increased an average of 1.9 bushels per acre per year, or 19 bushels every 10 years. Drought is typically responsible for substantial negative deviations from the trendline (-25% in 1988 and -22.5% in 2012; Figure 1). Severe widespread droughts will continue to negatively impact national average corn yields in the future, presenting as large deviations from a long term trendline. However, there are patterns that emerge in the yield deviation from trendline data. There is a tendency to have multiple years of deviation above trend (2003-2009 and 2014-2018) or below trend (1995-1997 and 2010-2013). The number of years differs, and can contain a contradictory year, but there is a pattern. This is not to say that the current yield indicates that for the next few years yields will be above trendline. The second is there is a smaller percent deviation (positive or negative) from trendline in recent decades. From 1965-1994, U.S. corn yields deviated (+ or -) from trendline by more than 10% in 11 years and by more than 7.5% in 20 out of 30 years (Table 1). By contrast, from 1995-2024, yields deviated by greater than 7.5% in only 3 years.
Table 1. The number of years from 1965-1994 and 1995-2024 with national corn yields 10%, 7.5%, 5%, or 2.5% higher or lower than the linear trendline
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