Managing nitrogen in corn effectively is not simply a matter of hitting a total pounds-per-acre target. How, when and where you apply that nitrogen can dramatically affect both crop performance and how efficiently each pound is used – especially when navigating the carbon penalty, says Ken Ferrie, Farm Journal Field Agronomist.
Understanding the Carbon Penalty
When soil warms in the spring, microbial organisms begin breaking down the previous season’s corn stalks. Because corn residue has a high carbon-to-nitrogen ratio (60:1), these microbes consume nitrogen as a food source to fuel the decomposition process.
During this phase, nitrogen is tied up by microbes and rendered unavailable to your corn crop, explains Ferrie. For example, a 215-bushel corn crop produces 6 tons of dry residue, requiring approximately 90 lbs. of nitrogen just to feed the microbes.
A telltale sign of the carbon penalty is yellowing leaves between the V2 and V6 growth stages. In fields where the nutritional gap is most severe, the crop is often referred to as being in the ‘ugly corn’ growth phase, characterized by stunted plants and reduced yield potential.
Establishing a Nitrogen “Floor”
To prevent your crop from stalling during the carbon penalty, Ferrie recommends establishing a minimum nitrogen floor. This will not be your total seasonal budget for nitrogen, but rather the amount required to carry young corn plants through the immobilization period.
“In our studies, we have found here in Illinois that it takes about a minimum of 60 pounds of N in corn after beans and 100 pounds in corn-on-corn or high-carbon cover fields to keep the corn from slowing down during the carbon penalty stage,” Ferrie explains.
To be effective, this “floor” of nitrogen must be accessible near the soil surface for young plants.
Planter-applied nitrogen is highly effective because it is concentrated in a band near the seed row. Ferrie notes that banded nitrogen has a “2x effect” when paying the carbon penalty.
“So, 30 pounds of planter-banded nitrogen behaves like roughly 60 pounds of broadcast nitrogen and can help keep the plant growing well through the carbon penalty stage,” he says.
Ferrie cautions against relying on anhydrous to counter the carbon penalty. “Anhydrous knifed in 7” to 9” deep, doesn’t count due to its location or distance from the root system. Corn has to grow roots down to the anhydrous to be able to pick that N up and it may be caught in the carbon penalty before it gets there,” says Ferrie.
He adds that ESN (Environmentally Smart Nitrogen) is also inadequate for the carbon penalty because its release timing is too slow for the early-demand window
Efficiency vs. Total Rate Reduction
While planter-banded nitrogen is highly efficient at protecting early growth, Ferrie warns against overestimating how much it allows you to cut from your total seasonal rate.
“While planter-banded nitrogen is twice as efficient as broadcast to get you through the carbon penalty, it is not efficient enough to cut your total N rate by 30 pounds,” Ferrie says. “With planter N you’re not stopping net immobilization. You’re just keeping the plant happy while net immobilization is happening.”
However, Ferrie says there are savings to be had. He estimates in-season banding can improve overall nitrogen efficiency by about 10 percent.
“If you were to band 30 pounds with the planter and apply 120 pounds sidedress, that 150 pounds would act like 165 pounds. So yes, you could cut your rate by 15 pounds in this case, and end up with as good or better outcome than broadcasting 165 pounds in the spring,” he says.
