Don't Tie Up Your Nitrogen: 3 Tips for Managing the Carbon Penalty

When the soil warms up in spring, the microbial organisms that break down the previous season’s corn stalks use nitrogen as a food source. When those organisms are busy breaking down the corn stalks, they tie up nitrogen that would otherwise be available in your fields for plant use. The tie up is often called the carbon penalty. The result: nitrogen is not available to your plant.

Corn residue has a high carbon to nitrogen ratio – 60:1. The higher the ratio, the more nitrogen is tied up to break down the stalk. And, the longer a stalk takes to break down, the longer the nutrient is unavailable to your crop.

To quantify the process for corn residue, let’s look at the table below:

YIELD (bu/ac) RESIDUE (tons/ac) N IMMOBILIZED (lbs/ac)
145 4 60
180 5 75
215 6 90
250 7 105
285 8 120

Source: Crop-Tech Consulting

A 215-bushel corn crop, for example, will produce six tons of dry residue, requiring about 90 lbs. of nitrogen to feed the microbes that will break down the residue. That’s 90 pounds of nitrogen that could be feeding your crop, but instead is busy breaking down residue.

The yellowing of a corn plants around V2-V6 is proof of the carbon penalty. The severity of the carbon penalty varies because it’s a biological system spurred by ground temperature and moisture. Microbe populations build as soil temperatures reach 50 to 60 degrees for a week with some moisture.

There are ways to manage carbon penalty. Ideally, you include a residue management program that accelerates the residue breakdown in fall and early spring to sync with the emerging crop. Here are the three ways to anticipate and reduce the impact of the carbon penalty:

  • Manage fall residue with stalk rolls. 360 CHAINROLL is designed to increase the action sites for microbial action. This allows the microbes to get a jumpstart on residue break down in the fall, well ahead of the growing season, freeing up nitrogen for the crop. This accelerated breakdown can also be accomplished with a residue sizing pass with a vertical tillage tool or disk.
  • Feed the microbes. In a high residue environment, provide the microbes with an easier form of nitrogen. They can use the more readily available form building their populations and starting the mineralization process sooner.
  • Feed the plant. Banding nitrogen with strip till or planter application systems puts nitrogen near the plant where it can be accessed in the V2-V6 stage when the nodal/crown roots are developing.

Managing nitrogen through V6 is critical because plants are establishing the maximum length and girth of their ears at this time. In a Base Plus approach, we need to make sure the crop has adequate nitrogen to keep corn happy until the side-dress application. At side-dress time, you have the ability to adjust rates to react to excessive carbon penalty, flushing rains or high levels of mineralization. The 360 Y-DROP nitrogen banding system – in early sidedress or mid-season application – provides flexibility in timing and placement to improve nitrogen efficiency through improved uptake.

Anticipating the carbon-penalty should be part of your overall nitrogen plan. Successful plans start to tackle the problem with the combine and end with timely sidedress application.

Photo: Stalks on the right show six months of breakdown with 360 CHAINROLL compared with conventional stalk rolls on the left. Faster breakdown reduces the microbe tie up that limit nitrogen availability.