The Purdue University Corn and Soybean Field Guide, the pocket guide that is the Bible of crop consultants and farmers alike, at least in Indiana, in its 2011 edition publishes a yield formula where the constant factor for dividing to get final yield is not always 90 as in the past. Instead, you can divide by a range of numbers, depending upon what growing conditions have been like.
The numbers increase for poorer conditions. That produces a smaller yield estimate. It may help temper the guesses, especially in a year like this one with high nighttime temperatures during pollination and the early part of grain fill. That situation result sin energy produced during the day in the form of sugar being use dup in respiration because temperatures are still high, rather than being converted into starch and placed in the kernel to form a plumper kernel.
Ranges in the guide are 75 to 80 for good conditions, 85 to 90 for average conditions, and 95-105 for poor conditions. Here's how this might affect your estimate. We'll use the same data you c0ollected in one field to compare these methods.
Suppose you found 30,000 ears in one/one-thousandth acre, found 16 rows of kernels and 36 kernels per ear. This is based upon sampling every fifth ear, forming averages, and then repeating the procedure at several locations picked at random within the field. The more areas you check, the more likely you are to get a true picture of what yield you can expect from the field.
Suppose you had excellent conditions. Maybe someone out there can actually say that. Let's use 80 as the factor for division. Then with the data above, you would get 17280 divided by 80, or 216 bushels per acre. Congratulations! If you're lucky, you have that one entered in a yield contest for Indiana.
Suppose your area saw more like average conditions. You decide to put the standard, 90,a s the dividing factor in the formula. Your estimate would now be 17280 divided by 90, or 192 bushels per acre. Still a good yield, but far less than the formula guessed based on an area that had excellent growing conditions all year.
Now for most of you, unfortunately. With less than 50% of the corn rated good or excellent by mid-August, a fair number of you can justify using the poor growing conditions factor. Say it's 100. So now it's 17,280 divided by 100, or 172.8 bushels per acre. That would still be a good yield for many folks this year, well above the August average yield estimate of 150 bushels per acre.
Still, it's over a 50 bushel swing. If you've used the 90 factor in the past, most people often say it's an estimate within 20%, plus or minus. Both of these estimates, high and low, are just over or under 10%. So adjusting the factor is just a way to hone in on your yield estimate.