In this week’s Boots In The Field podcast, Farm Journal Field Agronomist Ken Ferrie digs deeper into how farmers can be successful this season going to corn-on-corn.
He had addressed some initial questions on the topic a couple of weeks ago. If you missed that, you can check out that story at Corn on Corn Takes Root As Farmers Look for Profits
What follows are Ferrie’s answers to the main questions he’s received from farmers in the past week. He also takes a deep dive into some fertility considerations he wants farmers to pay close attention to, especially with regard to nitrogen use.
1. How do I select which fields to plant to corn on corn?
Use past yield histories to guide decisions, if you have a good track record of planting corn on corn, he says. If you’re new to corn on corn, he recommends looking at your bean fields that tend to be poor-yielding.
“Those would be ones that suffer from white mold, sudden death syndrome or have heavy cyst pressure,” Ferrie says. “I would not choose my best-yielding bean fields. We need them to stay in the rotation to keep any profits in soybeans this season.”
2. How do I pick the right hybrids for corn on corn?
Here too, any previous experience can help guide your decision. If you don’t have the experience with corn on corn, look to a neighbor who does and to your seed dealer who is experienced.
Look for hybrids that have good scores against seedling blights, and tend to handle allelopathic issues better.
“I would not go back-to-back with the same hybrid that you planted in that field last year for this season. I would switch them up. Otherwise, you will express the weakness of that hybrid,” Ferrie explains.
If you have a considerable amount of surface residue in the field – commonly a result of no-till, vertical tillage or even strip till – keep in mind that the residue is an inoculant for early disease. It’s also a potential bridge for late-season tar spot that occurred last season and can affect this year’s crop.
While no one can predict what kind of disease issues will for sure show up this season, you can protect corn with fungicides and seed treatments and intensive scouting for applying post-fungicide treatments.
“I would budget at least one fungicide application, and be ready for a second application for tar spot if it comes in later, as it’ll show up in these corn-on-corn fields first,” Ferrie says.
3. How do I meet the fertility needs for corn on corn and minimize the impact of the carbon penalty?
Last week, Ferrie talked about the carbon penalty and how to use the four Rs to manage around it – either banding near the plant or flooding the zone with nutrients to override the nitrogen deficiency caused by breaking down last year’s stalks.
This week, farmers asked Ferrie about broadcasting 100 pounds of nitrogen as urea and whether that would flood the zone enough to pay the carbon penalty? The answer is, maybe not.
“The rate is right, the placement is right at the surface, and the timing is right, but the product may not be,” Ferrie says.
“I go on several urea service calls every year where growers are dealing with yellow corn, and they think their urea is not working,” he adds. “Most of these calls will be in corn on corn, especially spring-chiseled corn on corn.”
Ferrie says a common scenario involves those fields where urea was surface-applied in the spring.
“In this situation, urea needs to be worked in right away or treated with a urease inhibitor. The urease enzyme that breaks down urea will be 10 times higher in that corn residue at the surface than in the soil below,” he says.
Don’t let this nitrogen gas off on you, he adds. When urea goes through the nitrification process, one of the first products produced is ammonium. Ammonium is like jet fuel to the microbes that are digesting last year’s stalks. If the soil temperatures are warm, these microbes can consume an amazing amount of nitrogen in the ammonium form.
“In our test plots, we can track this. Normally, after an application, we would see the ammonium values skyrocket when the urea starts to convert to ammonium. And when ammonium goes down, typically nitrates will come up.
In high-residue situations, ammonium can be consumed by the microbes, causing the ammonium numbers to fall in the soil, as it’s consumed by the microbes, but we don’t see a rise in nitrates in the soil. This nitrogen is immobilized for a period, causing the corn to go yellow.
“When I’m on a urea service call for yellow corn, the first thing the grower wants me to do is pull the nitrate test to see if the urea is still there. Well, we can’t check for urea. We can check the soil for ammonium, and we can check the soil for nitrate, but when the corn is yellow from nitrogen, I know both of these values are going to be low,” Ferrie says.
This nitrogen is not lost. Instead, it’s temporarily tied up until the microbes start to mineralize it back into the soil pool.
“Your corn will turn back green when this happens, but you may have already experienced a yield loss,” he says.
4. Why do soil microbes prefer ammonium as nitrogen?
Ferrie says soil microbes can use both ammonium and nitrate, but they prefer ammonium.
“Microbes are not very efficient with the nitrate, and they won’t use any nitrates if there’s ammonium available,” he says. “Once the ammonium has been completely consumed, they’ll start the process of consuming nitrates.
“I have personally seen 150 pounds of N as urea be consumed by the soil microbes. It literally disappears off the balance sheet for three to five weeks, then it’ll show back up as mineralization starts,” he adds.
Immobilization and mineralization are happening simultaneously, all the time. However, at certain times we have net immobilization, other times we have net mineralization. This is one of the reasons 100 pounds of N as 28% or 32% tends to work better when you’re flooding the zone, he says.
There, the N in 32% and 28% is half urea, and it still needs to be protected if applied to the surface; a quarter of the N is ammonium and can be used by the microbes immediately, and a quarter of the N is nitrate, which the microbes really don’t like and don’t want to use if they don’t have to.
“So the microbes go after the ammonium first, and then the urea when it converts to ammonium, they’ll go after it, kind of leaving the quarter of nitrate alone until the plant can feed on that,” Ferrie says.
Here are four other scenarios you could potentially encounter, depending on your practices using nitrogen:
1. If you are applying some N with the planter, which could carry your corn through until mineralization starts, Ferrie says you’re going to be all right with 100 pounds of N as urea surface-applied.
2. If the urea is on early, soils are warm and you’re planting later, you may be in a net mineralization period before the corn gets caught in the carbon penalty.
3. If soil nitrates are high due to over-application last season, such as if you were in a drought, you might get by as well.
4. If the corn stalks are not chiseled into the soil, where the fence posts rot off, the carbon penalty will be less, and you might be all right with the surface application.
5. What inhibitor is going to be most effective?
With 100 pounds of N as urea, Ferrie’s suggestion would be to only use a urease inhibitor to stop volatility – not a nitrification inhibitor.
The nitrification inhibitors hold the N in the ammonium form longer, which keeps it safe from loss due to water. But it stops it from converting to nitrate, which would be more accessible to the plant to use when the microbes consume all of the ammonium.
“I know I’m going to get some calls on that, but we’ve seen it in our plots multiple times,” Ferrie says.
“If you’re only putting on 100 pounds of nitrogen, I assume you will be sidedressing some later to take care of the back end of your corn’s nitrogen needs. Now, if you put 100 pounds of N on last fall as anhydrous, and you’re planning to put 100 pounds on this spring as urea, be ready to see some yellow corn or expect the corn to stall out, at least until your nitrogen starts to mineralize, or the corn gets a deep enough root system to find the anhydrous core,” he adds.
Most of the questions this week have come from growers who originally planned to go to soybeans, so Ferrie is assuming the fall N was not applied.
Kicking up the rate from 100 pounds and increasing it to 150 or 200 pounds of N might possibly overrun the microbes, allowing some ammonium to be picked up by the plant and some to convert to nitrate for the plant as well.
The problem here is this doesn’t leave much room for sidedress N which without it could leave your corn crop short on the backside.
Beware the fast escalation of temperatures this spring
Many times the yellow corn complaints come in to Ferrie’s office with rapid warming of temperatures.
“As temperatures explode rapidly, that’s usually when the phone starts ringing. This population of microbes doubles with every 10-degree soil temperature increase. So if the temperature is easing its way up, you get a little bit softer process out there. But if it jumps all of a sudden to 75 to 80 degrees and stays warm, that’s usually when trouble starts,” he says.
“Just remember, we do not want corn to have a bad day. When it’s yellow, it’s having a bad day and yield potential is getting dinged,” he adds.
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