Corn Illustrated: Here are signs that could indicate nitrogen ran short in these fields.
Classic nitrogen deficiency symptoms showed up in many cornfields late in the season. Yet many of those same fields yielded over 200 bushels per acre. How do you know if your fields ran short of nitrogen during late grain fill? How do you know if you should adjust nitrogen fertilization, or if deficiency was due to the season?
Dave Nanda, director of genetics for Seed Genetics Direct, says finding answers begins with reflecting on what you saw in the field.
“We saw nitrogen deficiency on lower leaves in the Corn Watch field soon after pollination,” Nanda recalls. “It was likely so dry, plants couldn’t take up nitrogen efficiently, even if there was enough in the soil.”
The bigger concern is if visual symptoms show up later during grain fill, Nanda says. There can be multiple reasons, ranging from a true shortage to plants remobilizing nutrients to fill kernels to reach a yield potential so high that it simply outstrips supply.
Here’s a closer look at three examples of N deficiency symptoms:
Symptoms around ear leaf.Classic yellowing at the tip of leaves working back along the midrib before corn reaches black layer indicates plants are running out of nitrogen. “What you don’t know is why,” Nanda says. “Ask yourself questions if you see symptoms. How much N did you apply? How and when did you apply it? Did weather conditions result in N loss?
“Perhaps yields are so good that plants used up all the N they could find. If so, the ratio of pounds of nitrogen per bushel of corn produced will be impressive. What you don’t know is how much higher yield might have reached with more N.”
Whole-stalk symptoms. Steve Gauck, a regional agronomy manager for Beck’s, Greensburg, Ind., walked a cornfield this fall where various symptoms indicated an N shortage. “It was irrigated, so lack of moisture wasn’t a factor,” he says. “Plants were tall. But they ran out of gas. Leaves were yellowish-to-brown most of the way up.”
Ears were shorter than expected in this field. Some ears curled at the tip, typical of nutritional stress. The field will yield well, but Gauck believes it could have yielded better if more nitrogen were available.
Low stalk-sample readings. Stalk samples were collected on a third field before black layer and sent to SureTech Labs. The field was planted May 31 and benefited from late-season rains. Ceres Solutions covered the cost of lab analysis. Results indicated only 15.5 parts per million of nitrate-nitrogen remained in the stalks.
“That’s very low,” says Betsy Bower, an agronomist with Ceres Solutions, based near Terre Haute, Ind. “Stalk test results can be difficult to interpret, but it indicates plants had very little N left. They used up nitrogen that was there.”
Coupled with leaf deficiency symptoms showing in this field, plants likely could have used more nitrogen. Yet yield will reach 200 bushels per acre, higher than expected for that field. Plants simply may have accessed all the nitrogen available.
