By Joe Janzen
This crop year, market observers have a heightened cynicism about the veracity of US national average corn yield estimates after data processing errors led to the release of an erroneous estimate from the National Agricultural Statistics Service (NASS) in the September Crop Production report (Blythe, 2026). While the error was later corrected, the environment of yield estimate skepticism has been reinforced by a sequence of NASS yield estimates that have lowered, raised, and then lowered again the national average yield. The most recent of these adjustments came earlier this week in the November Crop Production report. The split personality of these estimates, alternately bullish and bearish for corn prices, runs counter to the tendency for USDA crop production forecasts to be smoothed across the forecasting cycle (Irwin and Good, 2024).
This article puts this variation in the estimated US national corn yield in the context of past changes and considers what these changes might mean for both the final NASS yield estimate to be released in early January and for corn prices. The back-and-forth in estimated yield has clearly moved prices, especially the October report, which raised the yield estimate by nearly three bushels per acre and coincided with a 20 cent per bushel drop in price on report day. During the growing season, this kind of yield uncertainty tends to be positive for price (Janzen, 2021). To the extent there is greater remaining yield uncertainty in 2026 than is typical, the price impact may be minimized due to its timing.
US yield uncertainty alone cannot sustain high prices. Other market forces, especially US corn export use and South American production may already be responding to the ambiguity around US corn supply in ways that are bearish for prices. This presents both an opportunity and a threat for farms with a significant share of corn production to sell after January 1, a typical situation for grain farms in the US Corn Belt (Janzen, 2023).
Changes in the USDA Corn Yield Estimate
Corn yield estimates used in USDA market outlook information such as the World Agricultural Supply and Demand Estimates (WASDE) begin with a trendline yield estimate (an extrapolation of long-run trends in yield) released in May. USDA adjusts the yield estimate based on observed conditions in report releases through the growing season, typically in the monthly Crop Production reports released from August to November, plus a final estimate released in January.
Figure 1 plots the cumulative adjustments to the US corn yield estimate, highlighting the current 2026 crop year but showing time paths for previous crop years since 2014. In this period, the range of estimated corn yield updates has been within plus or minus ten bushels per acre of the initial trendline yield estimate. The figure shows this year’s estimates are well within the historic range. Estimated yield has been as much as nearly five bushels per acre below the initial 183 bushel per acre yield estimate, but remains relatively close to the initial estimate.
Source : illinois.edu