Corn needs nitrogen (N) throughout the growing season, though in varying amounts. The important thing is, "You want to keep enough nitrogen available during all corn growth stages so crop growth never slows down," says Ken Ferrie, Farm Journal field agronomist.
He says nitrogen works in corn like gasoline in a vehicle, fueling crop growth from emergence through maturity. A lack of nitrogen at any point along the way can cause the crop to sputter or stall.
"Corn that’s nitrogen deficient at the beginning of the growing season gives up yield potential," he says. "Nitrogen-deficient corn in the late reproductive stages costs actual yield."
From emergence to V8, corn plants consume less than 2 lb. of N per acre per day. While N uptake is not much because plants are small, don’t underestimate this stage because it impacts overall yield potential, Ferrie notes.
From V10 to V18, the plant consumes 5 lb. to 10 lb. of N per acre per day, known as the rapid vegetative growth stage. Once the plant has reached R1 and is pollinated, the daily usage backs off to about 2 lb. per day.
“When corn hits R1 and drops its daily usage to 2 lb. per day, you still have 60 days of this stage remaining,” Ferrie says. “It’s critical you meet the 2 lb. per day demand, whether you or the soil supplies N, to reach maximum yield potential.”
Knowing uptake needs dictates how aggressively you apply N based on growth stage, Ferrie says.
For example, if you pull a nitrate sample on May 10 (growth stage matters more than date) and the results are in the medium to low range, you need to react immediately because N usage is about to increase during the rapid vegetative stage.
However, if you pull the same sample on July 25, a medium to low reading is manageable because the plant only needs 2 lb. per day.
Ultimately, the more N your soil supplies, the less you have to apply. Fields with low-supplying power are more likely to respond to multiple N applications, even later in the season.
Here are six additional nuggets of information Ferrie provides to help you plan your nitrogen program in corn.
1. Assess the environment for every field; that is crucial in building a nitrogen program. Know your risk of nitrogen loss from leaching, denitrification and/or volatility.
2. Pick the right nitrogen sources, timing and placement. Doing those three things is much more important than trying to pick the right rate.
3. Assess the carbon penalty potential based on the amount and type of carbon left from your previous crop. Don’t forget to assess a carbon penalty for grass cover crops.
4. Consider that split applications and nitrogen inhibitors might be part of the balance of your nitrogen plan.
5. If corn greens up right after a sidedress application, it is telling you that the crop was waiting for the nitrogen and it was giving up yield potential during the process.
6. Season-long scouting is the only way to get a handle on nitrogen needs and management. Knowing when you run short is more important than knowing how much you ran short. As Ferrie emphasizes, "Scout, scout, scout and then make a plan."