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How USDA Figures Yields


In case you are among the many wondering why USDA would project such high trend-line corn and soybean yield estimates (163.6 and 44.5, respectively, for 2013), here’s an explanation from the Ag Forum in Washington today. They are based on weather-adjusted yield models that account for temperature and rainfall during the growing season.

USDA’s corn yield model indicates a 2013 trend yield of 163.6 bu./acre with a low-yield scenario of 154 bu. based on July temperatures one standard deviation above norm and July rainfall one standard deviation below norm. The high-end yield forecast is 170.1 bu. based on July temperatures one standard deviation below norm and July rainfall one standard deviation above.

USDA's soybean yield model indicates trend yield of 44.5 bu. with a low-yield scenario of 42.9 bu. and a high-end yield of 45.6 bu.

Even with the low-end yield forecast, U.S. corn production would be near 13.6 billion bushels, about 500 million above the previous record high, says Pete Riley, an agricultural economist with the Farm Service Agency. USDA’s trend-yield corn carryout estimate is 2.177 billion bushels, with a bullish scenario of 1.827 billion and a bearish scenario of 2.437 billion. The department uses the normal weather model, but the high/low versions are used for discussion.

USDA economist Paul Westcott adds that they studied the effects of January and May Palmer Drought Indexes on the following summer’s yields and found no statistic correlation: In other words, as we have been saying, it’s weather during the growing season that is important.


Editor’s note: Richard Brock, Corn & Soybean Digest's marketing editor, is president of Brock Associates, a farm market advisory firm, and publisher of The Brock Report.

TAGS: Management
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