Farm Progress reported on May 18 that recent weather patterns have left some farmers questioning whether their corn crops have lost nitrogen due to rainfall after a dry spring allowed for timely fertilizer applications. Dan Quinn, Purdue Extension corn specialist, said early signs of nitrogen deficiency may not appear until several weeks after emergence because young corn requires little nitrogen. “We don’t see much with nitrogen deficiency when corn is very young because it doesn’t need much nitrogen then,” Quinn said. “Even up until V6, it only uses 20 to 25 pounds per acre.”
As the crop reaches rapid-growth vegetative stages, typically around V10 or V11, symptoms such as yellowing midribs on lower leaves may become visible. This condition can be concerning up until tasseling if left unaddressed. “Corn up until tasseling should not have any nitrogen deficiency,” Quinn explained. “If you start seeing corn showing symptomology before tassel or even at tassel, it’s a good indication that you’re running pretty short.” He added that rescue applications of nitrogen are still possible and often effective during late-vegetative to tassel periods: “Corn does a really good job of responding to nitrogen rescue applications…we can save a lot of yield with that rescue application.”
Determining the correct amount for a rescue application remains challenging due to varying factors such as source composition and weather conditions affecting how much usable nitrogen remains in the soil. Quinn said, “It’s a very difficult question to answer, and we can kind of get a general educated guess because of the nature of nitrogen…It’s something that still, to this day, we struggle to understand.” Different fertilizer sources release nitrate at different rates; for example, ammonium sulfate converts quickly and may leach faster than other forms.
Nitrification inhibitors can help reduce volatility and retain more available soil nitrogen over time. Farmers are encouraged by Quinn to monitor timing closely: “If it’s showing up at V10 and it’s getting progressively worse, I’m probably going to make that decision,” he explained regarding when additional application is justified.
The economic impact is also significant this year as input costs remain high; farmers must weigh whether applying more fertilizer will offset potential yield losses from deficiencies or simply add unnecessary expense.
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