For more on this topic, check out The Buzz: How Big Are The 2014 Corn and Soy Crops?
We've all heard the saying "big crops get bigger" and to a certain extent it's true for corn yields. Changes in USDA's estimates for average corn yields during the year tend to reflect whether the crop is bigger or smaller than normal.
In years with below normal yields, the government's judgment tends to shrink from the initial assessment in August. In years with above average yields, those projections tend to get bigger.
The relationship over the past 40 years is statistically significant, meaning it's not merely the result of chance. But the yield size variable accounts for little more than a third of the variance in USDA's estimates, so there's obviously a lot more going on that makes it difficult to forecast average bushels of corn per acre in any given year.
Moreover, USDA's August crop report estimates aren't a reliable indicator of what to expect. The performance gets better with subsequent USDA crop reports, but there's plenty of room for error, even with these.
USDA forecast record yields in its August crop report nine times over the past 40 years, like it did this year. In four of those years, final yields did need get bigger. But they shrunk in five of the years.
The pattern is also difficult to predict when average corn yield per acre falls sharply. The most recent evidence of that came in the historic drought year of 2012, when USDA's final yield was the same as its August prediction. Yield estimates grew almost 8% during the 1988 drought year.
This year the wild card that might affect yields is acreage. Certified planted and failed acres reported Sept. 16 by the Farm Service Agency suggest USDA's official estimate, made by another arm of the bureaucracy, might be up to 3.4 million acres too high.
Changes in weekly crop progress and condition reports indicate the crop could be a little smaller than the USDA forecast in August, though overall ratings still point to yields close to those in the Sept. 11 USDA crop reports. The combination of slightly lower bushels divided by fewer acres still means the official corn yield estimate could get bigger down the road, perhaps reaching as high as 174 bushels of corn per acre nationwide.
For more, check out our coverage of the summer 2014 USDA crop reports.
July 11: USDA Crop Report Confirms There Will Be More Corn and Soybeans
Aug. 12: USDA Crop Report Shows Farmers Growing More Corn, Soy
Sept. 11: USDA Crop Report Forecasts Record Large Corn, Soybean Harvests
Also, calculate your own average corn yield per acre using these helpful tips.
Forecast Your Yield, but Remember Corn Kernels Are Bigger Today Than 30 Years Ago
Number of Rows Per Ear, Kernels Per Row Matter for Average Corn Yield