Nitrogen Deficiency Biggest Discovery From Field Walks

Symptoms above leaves worry consultant.

Published on: Sep 15, 2008

If what's happening in the Farm Progress Corn Illustrated plots near Edinburgh, Indiana, is any indication, what many agronomists and even marketing experts who study trends and try to compare current years to past years, feared just might be coming true. By August 1, after the big floods, many were comparing this year to 1993, the last time one in one-hundred to one in five-hundred year floods invaded the Corn Belt. That time only the western half was turned into a temporary replica of Noah's Arc. This time both the western and big chunks of the eastern Corn Belt felt the wrath of Mother Nature.

When it happened in 1993, USDA corn estimates fell each month from the first report issued in early August to the final report in January of '94. Some drops were significant, even from the October to final estimate. At the time many attributed it to loss of nitrogen, pointing out that the crops apparently ran out of gas, and didn't yield as well as they looked earlier in the season.

That scenario could in fact be repeating itself in many fields all across the Corn Belt. An Interstate 80 windshield survey from central Nebraska to northern Indiana, with another leg picking on Interstate 74 to Cincinnati, reveals lighter green-than-normal crops in many fields. Sometimes that happens in low spots or field corners where N may not have been applied evenly. This time it appears to be much more widespread, and is more noticeable as the season begins to wind down.

But many fields starting to 'dry up' and turn colors aren't following the normal pattern of senescence, notes Dave Nanda, president of Bird Hybrids, Tiffin, Ohio, and consultant for the Corn Illustrated project. What he found while checking the population study in the Corn Illustrated project he's found in many other fields. "Leaves are turning yellow at the tip, and it moves back up the midrib as it consumes more and more leaf tissue," he explains. "Eventually the tissue turns brown. But that's not how plants and leaves are supposed to dry down when they reach maturity normally in the fall. It's an abnormal pattern showing up because many fields are running out of nitrogen."

What concerns him most is when leaves above the ear leaf show this symptom. That's because at this point in the season, it's the upper leaves of the plant that do the most work, making sugars and energy to finish filling kernels on the ear. When those upper leaves die off early, there's every reason to suspect some sort of yield impact at harvest, he notes.

Walking the population study, Nanda concluded that no matter the planting rate or hybrid, many plants in the entire field were showing symptoms. The farmer cut back some on rate this year, but still applied more than 150 pounds per acre following soybeans.

"Its' not fair to say anyone made a mistake in recommending or applying less nitrogen, as long as the recommendation made sense in the first place," Nanda notes. There's no way to predict that the field will get 25 inches or more of rain from planting, May 5, through June 1. Last year the same field got about 2-3 inches during the same period. It's the excess rain that took the N down below where roots could reach it.

"You can't fertilizer based upon rolling the dice and gambling on an unusual year," he says. "We've still got to go with recommendations that make economic sense year in and year out."