Introduction – 2021 Corn Yield Unknowns
Every year, USDA’s early yield projections come under scrutiny for seeming large. 2021 is no exception. USDA’s May WASDE report estimated initial corn yield for 2021 at 179.5 bushels per acre (bpa), which would be the largest yet observed.
This week’s post considers the historic corn yield data, accounts for the upward trend in corn yields over time, and provides insights into the range of expectations for the 2021 growing season.
A lot can – and likely will – change between May and the fall, but it’s worth stepping back and considering the range of possibilities now.
Historic U.S. Corn Yields
Figure 1 shows reported U.S average national corn yields since 1988. The chart also includes a linear trend line of the data. From this, we can see that corn yields have increased by a rate of 2.13 bushels per year. This pace is rather small and arguably insignificant if you are comparing just a few years of data, but this upward trend is very significant over many decades.
Table 1 shows the underlying data plotted in Figure 1. Additionally, the final column of Table 1 reports the difference between the reported yield and the trend line, which is very important when considering the range of possible outcomes in 2021.
Finally, de-trending the historic corn yield data allows us to find that an “average” yield for 2021 would be 178.4 bpa. The largest reported yield was 176.6 bpa in 2017, hence the scenario where “record-shattering yields” are frequently observed given the upward yield trend. The yield in 2017 was +6.7 bushels above the trend yield for that year (169.9), which can be overcome relatively easily given the slope of the trend line (2.13 bpa per year).
Corn Yield Trends and 2021
In addition to a trend average of 178.4 bpa for 2021, the second thing we should consider is the range of possible outcomes. Table 2 ranks the observed historical departures from the trend.
Overall, yields have been less than -10 bushels off trend four times in 33 years of data (or, 12% of observations). As one would expect, 2012 stands out at -36 bushels.
On the high-end, 2004 stands out as the best historic corn yield at 18 bushels above trend. Also, on four occasions, yields have also been more than 10 bushels above trend.
Finally, Table 2 takes each year’s calculated departure from trend and adds it to the 2021 trend yield (178.4). This provides an idea of 1) the range of possible outcomes and 2) is helpful in benchmarking yield forecasts throughout the summer.
The first point to note is that 2012 is now almost a decade ago, which means the -36.2 departure from trend is equal to 142.3 bpa in 2021 terms. To that same point, the four times in history corn yields have been more than +10 bushel from trend also push the high-end of possible corn yield above 190 bpa. With these data and methods, a national corn yield >190 bpa is more likely than a national corn yield <140bpa.
Wrapping It Up – Setting Realistic Expectations for Corn Yields
To dig even deeper into the data, AEI Premium users can follow along with our 2021 Yield Model Project for weekly updates from three models tracking this year’s corn and soybean yield forecasts. A recent article evaluates this year’s fast planting pace and potential implications on corn yields.
With the 2021 growing season underway, chatter about yield expectations will become abundant. But first, we should “consider the base rate.”
Using yield data from 1988, a reasonable estimate for a trend yield in 2021 is more than 178 bushels per acre. Furthermore, the range of possible yields is quite wide. About 25% of historic yields have been extreme and more/less than +/- 10-bushel departures from the trend.
AEI Premium users can update their forecasts for the following question on this topic. It is helpful to consider the likelihood of yields being above (or below) trend.
While the growing season is just getting started, the goal of this corn yield guide is to provide a baseline of data to keep in mind.