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The Shrinking Odds of an On-Time Corn Crop

May 20. That's the average date for the slamming of the optimal planting window for corn in the Midwest. Using that date, recent planting progress data, and historical spring weather information, you should be able to get a good idea of your chances of getting this year's crop in the ground before you can truly consider yourself late.

May 20 may not be the optimal date everywhere in the Corn Belt, but looking region-wide, that's the best way to determine how late the nation's corn crop is in getting into the ground, say University of Illinois Extension ag economists Scott Irwin and Darrel Good.

"Acreage planted after that date would be considered to be planted late, and yield potential would be expected to be reduced as the percentage of the acreage planted late increases," they say in a recent university report. "We currently define the end of the optimum planting window for corn in the 18 major corn producing states to be May 20. The percentage of the crop planted after that date would be considered to be planted late."

This may be a common refrain for a lot of farmers who faced similarly cool, damp conditions a year ago. A lot of acres were delayed or not planted altogether, but a lot of corn was planted in a small window, effectively salvaging acres that were earlier thought lost to Mother Nature's bad spring behavior.

As of Wednesday, that leaves exactly three weeks to plant what USDA-NASS's weekly Crop Progress report showed to be just over 80% of the corn crop. Of the 21 days left, history teaches us your chances of having even half of that time under conditions favorable for planting corn aren't the greatest.

"We estimate the likelihood of zero to 21 days of suitable days based on the historical distribution of suitable days as reported in the USDA weekly Illinois Weather and Crops report for the 44 years from 1970 through 2013. Over the 44-year period, there were 11 or fewer suitable field days in that three-week period 52.3% of the time," according to Irwin and Good. "In other words, the median number of suitable field days during this three-week period was about 11 days, so that 'normally' farmers were able plant about half the time. The range of suitable days is surprisingly wide, with a minimum of four days and a maximum of 19 days. Note that there was a 15.9% chance of a week or less of suitable field days during this three-week period."

The entire U.S. corn crop's rarely planted on time, though. Those chances are greater this year, obviously, but even to stay ahead of the normal pace of "late planting," how much needs to get sown by May 20?

"Based on the historic distribution of suitable days for fieldwork, there is a relatively high probability that some corn acreage will be planted late in Illinois and particularly in the U.S. in 2014 unless the average planting rate per suitable field day over the next three weeks exceeds the average historic rate and is near the rate normally achieved only in the peak week of planting. Even in this latter case, there is more than a 25% chance that some of the U.S. corn crop would be planted late," the economists say. "Since zero late planting is rarely achieved, so that the probability of more-than-average late planting is probably a more meaningful calculation. For both Illinois (1960-2013) and the U.S. (1971-2013), an average of 15% of the corn crop has been planted late. To achieve less-than-average late planting, then, 53% of the Illinois crop and 66% of the U.S. crop needs to be planted over the next three weeks."

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