Source: Scott Irwin and Darrel Good, DEPT. OF AG & CONSUMER ECONOMICS, UNIV. OF ILLINOIS, 8/29/14

A widespread view in the trade is that the final yield estimate for the U.S. average corn yield in 2014 will be well above the USDA August forecast of 167.4 bushels per acre, perhaps as large as 175 bushels.  Much of the expected yield increase is based on the concept that "big crops get bigger," with support also coming from relatively high crop condition ratings late in the season.  A recent farmdoc daily article (August 20, 2014), however, revealed that not all big crops have gotten bigger in the past and that weather conditions this summer may not have been consistent with a large increase in the USDA yield forecast from August to January.  An implication of the expectation that the USDA yield forecast will increase substantially in future Crop Production reports is that the August forecast this year will have an unusually large forecast error.  The purpose of this article is to examine trends in the accuracy of USDA corn yield forecasts in recent years in order to provide an additional perspective on the debate about the U.S. corn yield in 2014.  Two previous farmdoc daily articles (August 19, 2011; September 1, 2011) and a research report earlier this year examined the accuracy of USDA corn yield forecasts.  We update those analyses here.

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