How USDA Trimmed Corn Yields

September 12, 2012 11:25 AM

USDA’s September Crop Report put the national average corn yield at 122.8 bu. per acre and the crop at 10.727 billion bushels. While still higher than our estimates of 120.25 bu. per acre and 10.478 billion bu., USDA’s estimates are tracking to our yield and crop pegs.

USDA’s September corn yield estimate was down just 0.6 bu. from its August peg, but that hides some significant changes in the underlying data. For example, USDA’s August yield estimate of 123.4 bu. per acre was based on an average ear population of 27,500 to 27,600 ears per acre. Its September yield estimate is based on an average ear population of about 25,700 ears per acre. That’s roughly a 7.1% decline in ear population from the August to the September Crop Production Report.

Another significant change is USDA’s assumed average ear weight. In August, the yield was based on an average ear weight of about .252 pounds. In September, the yield was based on an ear weight of about .269 lbs., a 6.7% increase.
So the yield change from August was based on a 7.1% drop in ear populations and a 6.7% increase in average ear weight.

We'll have state-by-state comparisons on News page 4 of this week's newsletter.

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