Every year, Ken Ferrie and his Crop-Tech Consulting team hear from farmers worried about yellow corn — but by the time they call, yield potential is already lost.
“Sometimes the problem is too low a rate of nitrogen, but other times it involves the wrong form of nitrogen,” says Ferrie, who also serves as Farm Journal field agronomist.
Problem and Solution
One common mistake is to apply only urea with a urease inhibitor on the soil surface after corn has emerged.
“The problem is the inhibitor keeps the fertilizer in the urea form, which corn plants can’t use,” Ferrie explains. “For plants to take up that nitrogen, it has to go through the nitrification process, to first become ammonium and then to become nitrate.”
That can lead to another problem: Soil organisms might consume too much of the ammonium before corn plants can take it up. To fix this, Ferrie says you might need to apply extra nitrogen to feed the microbes and prevent plants from being stressed.
“This is not the place for controlled-release products,” he adds. “They’re great for keeping urea locked up for 30 to 60 days, so it’s there later in the season. But you don’t want nitrogen to be unavailable while the carbon penalty is going on. However, you could blend those products with readily available forms of nitrogen to make sure your front-end application carries plants into the rapid-growth stage.”
Put Fertilizer In Its Place
The most effective way to pay the carbon penalty (temporary immobilization caused by exploding microbe populations) is to band fertilizer close to the corn plants.
“You keep the plant happy while microbes battle for the nutrients in the soil. And fertilizer banded within reach of young plants has at least twice the horsepower — 50 lb. per acre of nitrogen applied with the planter is more effective at managing the carbon penalty than 100 lb. broadcast.
“Nitrogen and sulfur can be banded with a strip freshener in no-till and strip-till,” Ferrie continues. “Nitrogen, phosphorus and sulfur can be banded with the planter. If you apply fertilizer in the seed furrow, watch the salt load and the amount, so you don’t burn the seed.”
Not All Banding Is Equal
“While banding anhydrous ammonia is efficient, the nitrogen is in the wrong location to pay the early carbon penalty,” Ferrie says. “From emergence to the V6 or V7 growth stage, the roots will be too far away to reach the nitrogen, and plants will run short of nitrogen.
“You sometimes see this effect in the spring if anhydrous ammonia was applied at an angle to planting,” Ferrie adds. “Plants over the ammonia track green up, and the field takes on a striped or streaked appearance. Those streaks tell you a nitrogen shortage is slowing growth. The same thing happens with strip-tilled anhydrous ammonia until roots get deep enough to find the nitrogen; but there are no streaks, so it’s harder to see.”
Confirm Nitrogen Rates With a Plot
How do you know if your decisions were correct? Ferrie recommends a plot comparing front-end nitrogen rates to learn how much nitrogen is required to pay the carbon penalty (from emergence until the plants are about knee-high). Put it close to your house where you’ll see it every day.
“Start with a zero-nitrogen strip, then walk up rates 30 lb. at a time until you get to 150 lb. per acre,” he suggests. “Then watch the field. When soil starts warming fast and corn enters the rapid growth stage, plants will turn light green to yellow and slow down their growth rate within days.
“At this stage, you should see a difference between the zero and 30-lb. rates. Corn will get greener and bigger with each 30-lb. increase until the carbon penalty is met. When corn no longer shows a visual response to increased nitrogen, you have paid the carbon penalty.”
Sidedress the remainder of your nitrogen after plants reach the V6 or V7 growth stage.
What Your Nitrogen Plot Can Tell You
An on-farm nitrogen plot can help you find your most efficient rate of nitrogen, Ferrie says. Here’s an example of a test plot from a Farm Journal study on an Iowa farm. It is based on corn selling for $4.77 per bushel and nitrogen costing $1 per pound.
The operator applied 30 lb. of nitrogen per acre in the fall and sidedressed the rest after the corn had emerged. “Clearly, 98 lb. of nitrogen per acre was not sufficient,” Ferrie says. “148 lb. per acre was better, bumping yield from 188 bu. per acre to 224 bu.
“Increasing the nitrogen rate by another 50 lb., to 198 lb. per acre, yielded 26 more bushels,” Ferrie continues. “The grower needed only about 10 more bushels to pay for the additional fertilizer.”
But adding another 100 lb. of nitrogen per acre took the grower past the point of maximum efficiency. “He would have needed about 20 more bushels of corn to pay for that fertilizer,” Ferrie says. “But it only increased yield by 15 bu. per acre.”
