Pulling a corn yield check prior to black layer can be tricky. But Minnesota crop consultant and farmer Mark Nowak has fine-tuned a process that he finds close to yield monitor accuracy.
"Most corn yield calculations or formulas use ear rows and kernels per rows times the population. But what this process doesn't do is take into account the depth and weight of the kernel," said Nowak.
"I walk into the cornfield and randomly stop, turn around and then pick 10 ears all in a row. I take these 10 to my shop and put them under air from a fan until the kernel moisture dries so that the ears can be shelled in my hand-crank sheller -- typically this is 24% (moisture) or less," he said.
From there he weighs the sample with an ounce scale. Dividing that corn weight by 10 gives an average weight per ear of shelled corn. From there, the math gets easier. Take the average ear weight per ounce times the population, divide by 16 (lbs.) and divide that by 56 (lbs. in a bushel).
From there, he adjusts the yield for the moisture in the sample. "I use 1.3% shrink for every point of moisture. To remove any field yield variability, he reduces the resulting yield estimate by 5%.
"My experience is this process comes within 5 bushel per acre from actual harvest results most of the time," Nowak said.
Here's an example of how Nowak's calculations worked:
-- Picked 10 ears at 50% milk line.
-- Air dried 10 ears to 23% moisture and shelled.
-- 10 ears weighed 83 ounces (8.3 ounces per ear).
-- Population of 33,000 x 8.3 = 273,900 ounces off 23% corn.
-- Divide 273,900 ounces by 16 = 17,118 lbs. of 23% corn.
-- Divide 17,118 lbs. by 56 = 305 bpa of 23% corn.
-- Adjusting to 15% = 8 points x 1.3 = 10.4% adjustment to yield (305 x 89.6% [100 - 10.4]) = 273 bpa.
-- Final yield variability adjustment 273 x 95% = 259.35 bpa.
Nowak dried the sample to 16%, and the test weight check came back at 56.3, which was good considering the corn was only 50% milk line. Given good growing conditions, it should gain a bit more weight as it moves toward black layer. Test weight is a measurement of bulk density or weight of a unit volume of grain and can range considerably.
"Ideally, the most accurate way to sample is to wait until black layer, but this year, we are 10 days to two weeks behind on maturity and want to get a jump on yield analysis," he said of the south-central Minnesota crop.
"After this sample resulted in the prospect of a corn crop to more than fill my bins, I went to the elevator and cash contracted some bushels to take advantage of $6-plus corn. Which, if my yield estimate verifies, will be a very profitable sale," he noted.
Nowak also does the yield sampling on a few different hybrids to offer some clues for seed selection for planting the following year. He'll also do some weigh wagon checks.
Each season, various growing regions are thrown environmental curveballs, so getting out to your sample fields is a good step. Nowak said farmers often ask how he does his calculations, and he enjoys educating others on the process so they can make informed decisions.
There are several ways of doing fall corn yield checks ahead of the combine. Read more about those formulas here: https://www.dtnpf.com/….
For a look at how yield tours estimated the crop this year go to: https://www.dtnpf.com/….
Pamela Smith can be reached at firstname.lastname@example.org
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