Robb Ewoldt had a hunch. But he didn’t fully realize how corn yields declined until he compared check strips of corn harvested at 26% moisture vs. later-harvested 16%-moisture corn in 2024.
“There was 25 to 30 bushel [per acre] yield loss — about a 10% yield decrease — from harvesting later [at 16% moisture] in that 140-acre field,” says the Davenport, Iowa, farmer.
Steve Luther noticed the same pattern occurring whenever combines switched from corn to soybeans and back to the same cornfield seven to 10 days later.
“Corn in that field could be making 245 bushels an acre, but when we came back, the yield would drop around 12 bushels an acre,” says Luther, who manages Stine Seed Farm, Adel, Iowa. “You think to yourself, ‘What’s going on? Is there a hole in the bottom of the combine?’”
Phantom yield loss
There’s no question that as natural drydown occurs, corn contains less water. Ultimately, less corn is left to sell. There’s a belief, though, that a phenomenon called phantom yield loss slices yields even more.
True to its name, this proposed yield loss is akin to a phantom mysteriously snatching away dry matter — and, ultimately, yield — over several days to several weeks in the fall. The theory is that as grain dries and releases moisture, kernels also release carbon dioxide. This triggers lower kernel weight and lower yields.
However, mechanical damage and natural causes also play a role.
“There are all kinds of ways that corn can be lost during harvest,” says Charlie Hurburgh, an Iowa State University Extension agricultural engineer. “Stalks can lodge or drop ears. Kernels can shatter on the combine head, or end up as fines in the grain tank, or go out the back of the combine.”
What studies say
One study that phantom yield loss believers cite is from Purdue University. It documented about a 1% dry matter loss (and corresponding yield loss) for every 1% decrease in corn grain moisture from 28% to 18% from 1991 to 1994.
Later studies by Ohio State University and the University of Nebraska couldn’t duplicate these results. In 2016 and 2017, ISU researchers launched a similar study to determine whether dry matter loss accompanied grain moisture loss.
They evaluated two sites over two years, with two planting dates and three hybrids with different relative maturities at each site. Researchers hand-harvested each plot to nix any losses from mechanical damage. They also oven-dried samples to determine moisture levels.
Hurburgh says moisture meters tend to read low in wet corn and even lower in hand-harvested corn. This can alter findings by increasing converted dry weights, he adds.
“We started harvesting at roughly 30%, right after physiological maturity,” Hurburgh says. “We progressively harvested the field at later dates with drier corn, tracking it by measuring kernel weights. We couldn’t find any differences in moisture-adjusted kernel weights. We even had one hybrid that kept gaining dry matter as it dried down.”
University of Illinois researchers found yields stayed similar at different moisture levels through a month-long harvest period in 2023 and 2024 trials. As in the ISU study, they hand-harvested plots to eliminate mechanical damage as a cause of yield loss.
Harvest dates, moisture and yields for 2023 were:
- Sept. 11, 26.8% and 206 bushels per acre
- Sept. 18, 23.3% and 213 bushels per acre
- Sept. 25, 20.2% and 213 bushels per acre
- Oct. 2, 18.5% and 212 bushels per acre
- Oct. 9, 17.3% and 212 bushels per acre
The pattern was similar for harvest date, moisture and yields in a higher-yielding 2024:
- Oct. 3, 25.8% and 295 bushels per acre
- Oct. 11, 20.9% and 294 bushels per acre
- Oct. 17, 19% and 300 bushels per acre
- Oct. 24, 17% and 303 bushels per acre
- Nov. 1, 16.4% and 299 bushels per acre
“It is interesting to note there were very different yield levels and weather patterns for the two years, but the same result occurred,” says Connor Sible, a University of Illinois research assistant professor.
If yield declines occur, Sible agrees with Hurburgh that mechanical reasons or weather could be the culprit. Ditto for wildlife feeding. A raccoon that eats one 500-kernel ear in a 250-square-foot area replicated over 1 acre can spur a 1 bushel-per-acre loss, Sible says.
“The longer that fields sit, the more chance that grain ends up in an animal’s stomach,” he adds.
Failure to recalibrate moisture yield monitors also may explain losses.
“Yield monitors will not read 24% and 17% moisture the same way,” Sible says. “If farmers do not recalibrate yield monitors, this could explain the bulk of the change.”
When reviewing studies, Hurburgh says it’s important to confirm that yields or weights have been mathematically adjusted to 15% moisture for comparison purposes. That’s akin to what seed companies use with plot comparisons, he says.
Maybe, maybe not
Still, ambiguity exists. A 2018 to 2022 Nebraska field study by Pioneer found yields declined an average of 9.1 bushels per acre with later harvest compared with earlier harvest. It found neither that change in grain moisture or duration in time between an early and later harvest had any relationship with the yield difference.
“The reason it's called phantom yield loss is because we still don't have a 100% explanation,” says Mike Swoish, a Pioneer field agronomist.
Phantom yield loss may or may not be occurring, Luther admits.
“There are a lot of things that lead to losses as corn starts to dry on its own,” he says. “Machine damage accounts for some of that. But we always see a yield gain by starting harvest in the 24%-to-27% range before we work our way down in the 18% range.”
‘Pretty cool’
Ewoldt’s check plot findings combined with research he conducted spurred him to start harvesting corn at 27% moisture. Aiming to harvest his estimated 1,100 acres of corn then could save an extra 20 bushels per acre on average, he says. Depending on corn prices, he figures this could result in annual gross corn sales of $75,000 to $100,000.
“Those are a lot of bushels we couldn’t otherwise sell,” he says.
To manage the high-moisture corn, he built a drying and storage system that receives 8,000 bushels of corn hourly in a 25,000-capacity wet holding bin. From there, corn travels to a mixed flow dryer that can remove 10 moisture points from 800 bushels hourly. Then, corn moves into two storage bins with a combined 175,000-bushel capacity.
The $1.3 million investment has a 10-year payback, Ewoldt says. So far, it has trimmed drying costs down to 1.4 cents per moisture point, far below that of commercial drying costs, he says.
The additional storage also enables Ewoldt to capture grain market carry. This refers to when future contract months are worth more than the current month. Farmers who store grain can capture the “carry” in future contract months.
“Last year, we were able to pick up about 70 to 80 cents per bushel that way,” Ewoldt says.
The storage and drying expansion also is rooted in a belief that a late friend had, he says.
“He always told me that if corn got below 25% moisture, we were losing money,” Ewoldt says. “We finally got to a spot to show him he was right all along. He would have thought this was pretty cool.”