Estimate corn yields, beginning now

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We have had two weeks of crop ratings for corn, with a decline in condition to 72% good to excellent from 77% good to excellent a week ago.  That was the USDA’s crop progress report on Tuesday.  While various Corn Belt state’s corn crops are going down in quality, this is the time of year that yields need to be determined.

On May 21, USDA reported the condition of the corn crop was 79% good to excellent in Illinois, 70% good to excellent in Indiana, and 81% good to excellent in Iowa.  However for the current week, those conditions had declined in Illinois to 72%, in Indiana the decline was to 66%, and to 77% in Iowa.

University of Illinois agricultural economist and marketing specialist Darrel Good says the most important aspect of corn yields at this time of the season is timely planting.  While the planting dates this year were earlier than any others, there are indications that yields could have been very good based on the early dates.  What is more, Good says, “This year, only four percent of the corn crop in the 18 major corn producing states was planted after May 20.”  That compares to 18% average for the past 25 years.  There have been a handful of years when less than 10% of the crop was planted after May 20, and in half of those years the yield was within two bushels of the trend yield, but in the others, it was well beyond, and both below and above the trend yield.

However, Good says summer weather conditions ultimately determine yields, but “The small percentage of the crop planted late this year suggests that the U.S. average yield will be higher than if a normal percentage had been planted late, but the level of yields is still to be determined.”  In addition to planting date, Good says the weekly crop condition reports are the second most important early indicator of yield.  He says there is a strong relationship between the final yield and the weeks going up to harvest with rating that are in the good to excellent category.  As indicated previously, the condition report for the current year has already moved to a lower point, and if it is to end strong, it will have to have a major turnaround and make up the losses.

While planting date and crop conditions are important, Good says a combination of moisture and temperature will quickly become the major elements in determining crop size, “At this juncture two important developments may be required in order to maintain high yield expectations. The first is some convincing evidence that the relatively long period (8 months or so) of above average temperatures is giving way to normal or below normal temperatures. The second is for soil moisture deficits in important areas of the central, eastern, and southern Corn Belt to be eliminated.”

So far there have been no indication of temperature trends, but there has been plenty of data about soil moisture levels.  Illinois topsoil has moved from 33% short and 64% adequate last week to 48% adequate and 52% short and very short this week.  Indiana last week reported topsoil moisture was 36% short and 52% adequate, but this week it is 28% adequate and 71% short to very short.  And Iowa last week indicated topsoil moisture was 37% short and 55% adequate, however this week it is 47% adequate and 51% short to very short.

The IL ag economist says another critical factor is planted and harvested acreage, which will be updated on June 29th with USDA’s Planted Acreage Report.

Summary:
Corn yields are a function of timely planting, which was early this year and should be quite favorable.  However, they are also a function of the amount of corn in good to excellent condition toward the end of the growing season, as well as a combination of temperature and moisture through the growing season.  So far temperature has not been too far beyond the norms, but soil moisture is short and growing shorter, which is not beneficial to high corn yields.

Source: FarmGate blog


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