The old adage holds that “big crops get bigger;” and we must have a big crop because the production forecasts from USDA continue to grow. While many Cornbelt farmers may contest that projection, there is some corroborating evidence that USDA’s estimates may be on track. The NASS statisticians complete their objective field surveys with actual measurements of crops. At the same time, economists at the University of Illinois, joined by a meteorologist, have developed a model that makes crop size prediction in a completely different manner. What have they found?

Throughout the course of the summer, University of Illinois ag economists Scott Irwin and Darrel Good, along with meteorologist Mike Tannura have been refining their 2009 crop size estimates based on several factors. Their Final Yield Forecast makes use of a crop weather model that estimates the impact of technology (trend), state average monthly weather variables, and portion of the crop planted late on state average yield. Their latest update includes August precipitation and temperatures to project yields in Illinois, Iowa, and Indiana.

The forecasters repeat the fact that July was the coldest month in their long term sample and August was at the low end of their historical records, two factors that may reduce the ability of their model to accurately predict the impact of temperatures on yield. So far the track record has credibility. It predicted 97% of the variation in corn yields and 92% of the bean yields over 1986 to 2008. The Illinois forecasters used the USDA September crop report’s acreage update for 80.007 million acres of corn and 76.767 million acres of soybeans.

The economists report their forecasts based on the crop weather model are “substantially higher” than last month, based on the assumption of average August weather and “marginally lower” than the forecast based on the assumption of good August weather. They attribute that development to the positive impact of August precipitation and temperature on yield prospects.

Based on the September 6th report that 69% of the corn crop was in good to excellent condition, the US corn yield forecasts range from 158.8 to 170.2 bushels per acre. That puts total production between 12.705 billion bushels and 13.621 billion bushels. The average is a 164.5 bushel per acre average yield that provides a 13.163 billion bushel crop. Friday’s USDA forecast projected a 161.9 bushel crop and a 12.955 billion bushel production. Based on the September 6th report that 68% of the soybean crop was in good to excellent condition, the US soybean yield forecasts range from 44.6 to 45.2 bushels per acre with production ranging from 3.422 billion acres to 3.466 billion bushels. The average is a 44.9 bushel yield that produces a 3.444 billion bushel crop. USDA forecasts a 42.3 bushel per acre yield average with production estimated at 3.245 billion bushels.

For Illinois, the crop model projects a 178 bushel yield on corn and 48.9 bushel yield for soybeans. For Indiana the crop model projects a 170.6 bushel yield on corn and 47.4 bushel yield for soybeans. For Iowa the crop model projects a 201 bushel yield on corn and 50 bushel yield for soybeans.

Summary:
Actual field examinations by USDA statisticians have forecast a larger corn and soybean crop than was expected in August, and a crop weather model developed at the University of Illinois has corroborated that estimate. Illinois is expected to have a 178 corn yield and 44.9 bushel soybean yield. Iowa is expected to have a 201 bushel corn yield and 50 bushel soybean yield and Indiana is expected to have a 170.6 corn yield and 47.4 soybean yield. Nationally, the Illinois crop weather model projects a 164.5 bushel corn yield with production at 13.163 billion bushels. For soybeans the crop weather model projects a 44.9 bushel yield with a 3.245 billion bushel crop.