Corn is moving into the rapid growth stage across much of Illinois, just as a hidden yield thief wakes up beneath the residue. Farm Journal Field Agronomist Ken Ferrie says the “carbon penalty” is about to appear, and some farmers’ nitrogen plans aren’t ready for the hit.
I do anticipate somewhat stronger-than-normal carbon penalty here locally, especially in our corn-on-corn fields,” says Ferrie, who’s based south of Bloomington, Ill. “This is due to the low amount of stalk breakdown that we got through the fall and winter.”
The carbon penalty, he explains, is tied directly to carbon load and soil temperatures. Once minimum soil temperatures stay above about 60°F and daytime highs run in the upper 70s to low 80s for roughly five days, soil microbes “explode” and start chewing through residue at a rapid pace. In the process, they temporarily tie up nitrogen that young corn plants and small soybeans need.
He expects this year’s carbon penalty to kick in “next week” as temperatures rise in his area, overlapping squarely with what he calls the ugly corn phase. He encourages farmers in other parts of the Midwest to evaluate their risks, as well.
When ‘Ugly Corn’ And Carbon Penalty Collide
Ferrie says most May-planted corn in central Illinois is now at V3 to V4, the point when plants begin handing off from seed roots to crown roots. This is the point when things can fall apart in the crop.
“If anything has interfered with crown root development, this handoff is messed up,” Ferrie says. “The seed starch is enough to build a pretty impressive plant up to like V3, but if the handoff is missed, a uniform field can start to come apart in a hurry.”
Sidewall smearing, compaction, herbicide injury, insect feeding and dry soils can all undermine crown roots. Layer a strong carbon penalty on top of weak root systems and fields can turn “ugly” fast.
“You have the ugly corn phase of crown issues, and then if you compound that with a carbon penalty, it can make for some pretty tough-looking stuff,” he says.
So far, most ugly corn service calls Ferrie is making are in April-planted fields. But with warmer weather coming and more corn reaching the critical V3 to V4 window, he expects May-planted acres to start showing problems in the next 10 days.
Diagnosing The Problem: Roots Or Nitrogen?
When scouting fields that look rough, Ferrie urges farmers to sort out whether they are looking at poor crown root development, a nitrogen (N) shortage tied to the carbon penalty, or a combination of the two.
If the primary issue is a nitrogen deficiency from carbon tie-up, farmer options are limited and time-sensitive.
“If it’s an N deficiency due to carbon penalty, there’s not much you can do but maybe move up your sidedress timing,” Ferrie says.
He recommends banding nitrogen closer to the base of the plants and timing nutrient applications ahead of or with a small rain to help get N into the root zone.
If poor root development is the main culprit, the fix might look different. When sidewall smearing or a dry surface layer leads to rootless corn syndrome, Ferrie says mechanical intervention can pay.
“You may consider row-crop cultivating as soon as you can get through and roll some soil around the base of that plant,” he advises. “This will stimulate crown roots and brace roots to trigger quicker.”
Cultivating, however, is not a cure-all. Ferrie cautions that in situations where last year’s herbicide has carried over, working the ground doesn’t typically solve the issue.
Rethinking Your Nitrogen Strategy And The 4Rs
Ferrie says some growers are discovering their nitrogen plans did not fully account for the carbon penalty, especially where they switched to fall-applied anhydrous to save on costs.
“Some of the issues we’re dealing with are caused by guys switching to fall-applied anhydrous for cost savings—and we all need those—but didn’t hold enough N back to pay the carbon penalty while the roots are trying to get deep enough to find that anhydrous pan,” he says.
That risk is amplified in corn-on-corn, where residue loads and microbial demand are highest.
“If this shows up to be a problem consistently, you need to rethink your 4R program when it comes to nitrogen,” Ferrie says. “If you’re not planning on pulling nitrates, be sure to look over your nutrient plan. If you’ve changed it or you’ve raised that yield goal, we’ll need to adjust those rates for you, especially if you’re running variable-rate nitrogen.”
Ferrie notes that early nitrate samples look “pretty nitrogen-friendly” this season in his area, but he’s already fielded calls from growers surprised to see sidedress rates jump 30 to 60 pounds above the original plan once fall fertilizer shortfalls and higher yield goals were factored in.
Soybeans Can Hit The Wall, Too
Soybeans are also vulnerable to the carbon penalty and can stall as well.
“Soybeans can get caught in the carbon penalty if they’re smaller than that V3 size,” Ferrie says. “They don’t produce much nitrogen until they’re in the V4 range. Older beans will roll right through it without any trouble, but the last-planted beans could stall out in that carbon penalty, and it could take a couple weeks to get them back going again.”
In the coming two weeks, Ferrie wants farmers and scouts evaluating root development, nitrogen status and residue load.
“Those sins of spring will start to show up in that ugly corn phase,” he says. “The key is to figure out what you’re dealing with, and then decide if you need to move N sooner, change how you’re applying it, or get out there and help those roots do their job.”
You can get all of Ken Ferrie’s recommendations in the latest edition of his Boots In The Field podcast at the link below:
