I've estimated yield in one 60-acre field at 42 bushels per acre, checking each soil type and doing the best job of estimating and averaging as possible. Odds are it will yield fewer than 42 bushels per acre. For one thing, it will be hard to get all the kernels off small cobs that were counted in the estimate, without putting a lot of pieces of cob and other trash in the grain tank.
More importantly, since I used the same formula I always use, it likely is overestimating the yield. That's because there is a factor that represents number of kernels per bushel as a correction factor. Normally, number of ears in one/one-thousandth acre are multiplied by rows of kernels and kernels per row, then divided by the factor, 90.
Mark Lawson, an agronomist with Syngenta, Danville, Ind., says he's been using 100 instead of 90 in his estimates so far this season. That's because he says the kernel depth is less than normal. If kernels are smaller in size, it will take more to make a bushel. Hence, he believes that it's important to back down the formula. Using 100 instead of 90 as the division factor in the yield estimation formula would produce about 10% lower yields.
"The kernels just aren't as deep," he says. "Some of the hard-hit areas have received rains lately, but it was likely too late to help corn fill kernels out more. We've had enough growing degree days that many of the hybrids are at or very near black layer. Once black layer occurs no more sugars can be placed in the kernels."
You can go as high as 120 for the division factor in the formula. If you've got a significant number of ears with missing rows, and rather large round, plump kernels next to missing rows, going further than switching from 90 to 100 as the division factor may not be necessary.