August 15, 2008
AMES, Iowa — The government yield estimates released Aug. 12 had positive news predicting an above trend line yield for corn. Iowa State University agronomists say the estimates are in line with the five-year average.
But those interested in the report released by the National Agricultural Statistics Service (NASS) need to understand what the report is measuring. "This is a measure of the number of corn plants and ears per acre," said extension corn agronomist Roger Elmore. "This report does not measure ear development. The Sept. 12 report will be of greater interest to farmers when additional data is collected."
Next month's crop yield report will take into account the girth and length of ears. This extra data will give a more precise measurement of yields, said Elmore.
All of the yield reports compare a snapshot of the current crop development with an average of the last five years of data. Trend line yield for Iowa, typically the nation's largest corn producer, is 167 bushels per acre. The NASS estimate for 2008 is 171 bushels per acre for Iowa.
Not factored into crop yield reports is potential weather. The yields in the report are based mainly on the number of developing ears and assumes both ears and weather will be like the average of the past five years, said extension climatologist Elwynn Taylor.
"The current cool weather is helping the crop, but things are currently on the dry side of usual," said Taylor. "If the weather heats up with a string of mid-90 degree days, the corn condition could change very quickly for the worse. This crop is very vulnerable."
Taylor said the corn crop is already worsening in parts of Ohio and Kentucky due to a lack of moisture.
Elmore and Taylor agree the USDA number may be a bit high, but the statistical accuracy of the report is solid. "NASS measures 400 random plots in Iowa," said Elmore. "It's very good data."