The following information is a Web Extra from the pages of Farm Journal. It corresponds with the article "Tap Hybrid N Efficiency” by Margy Fischer. You can find the article on in the Mid-November 2009 issue.
If you don't understand how carbon impacts nitrogen (N) availability, you are setting the stage for a field that grows slow after emergence and never catches up to meet its yield potential—even if you do everything else right. Understanding the carbon/nitrogen cycle is critical—especially in continuous corn or other situations with large volumes of crop residue.
The yellowing of the corn shown here was created by soil microbes immobilizing N. The tent site from Corn College 2008 shows how removing all the cornstalks sidestepped the carbon penalty. No N was applied on the right and 110 lb. was applied on the left. Although N used by microbes becomes available later, it is temporarily immobilized and made unavailable to plants.
The processes of immobilization and mineralization happen continuously throughout the season. At different times, there can be net immobilization or net mineralization. You have to apply enough N on the surface to both feed the microbes and ensure that enough N is still available to feed the corn plants during net immobilization.
Key Factors to Remember:
- High volumes of crop residue that are incorporated into the soil will provide an abundance of food for soil microorganisms.
- Large amounts of residue can cause microorganism populations to explode.
- Climate is a huge factor.
Northern corn-growing areas, due to the shorter growing season, will have more carbon left in the soil to decompose in the spring, which will cause more immobilization.
Southern climates, on the other hand, may decompose carbon too quickly, lose the nitrogen and leave soil without a residue cover.
Timing and placement are critical. Nitrogen applications need to be positioned to pay the early season carbon penalty with a surface application and protect from loss later in the season by banding at sidedress for ear fill. As shown, the efficiency—and yield—from 220 lb. of nitrogen can be radically different.