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Rescue nitrogen

Agriculture.com Staff 07/06/2010 @ 5:22pm

Choosing a nitrogen rate is hard enough the first time. It's even harder the second time when you're trying to rescue corn after heavy rains have stolen part of the first application. At that point, it's hard to determine how much nitrogen was lost, how much is left, and the yield potential of a crop that may be struggling to survive in a wet field.

It's a situation many growers found themselves in this spring. Ross Johnson, who raises seed corn, commercial corn, and soybeans near Watseka, Illinois, was one of them.

He had applied 90 pounds of nitrogen (N) per acre after planting on two of his seed cornfields. (He was also counting on chicken manure applied earlier to supply some nitrogen.) Then, in one four-day period in early June, those fields received 9 inches of rain.

When the fields dried out, Johnson used a tractor-drawn applicator with coulter/nozzle assemblies to apply 60 pounds of N to one of the seed cornfields. Meanwhile, his fertilizer dealer used a high-clearance machine equipped with solid-stream nozzles to apply 60 pounds of N to the other seed field, which had taller corn. A light rain soon took that nitrogen in.

Because Johnson had never been in that situation before, he wasn't sure he had done the right thing. That's when he sought other people's opinions in the Crop Scouting discussion group of Agriculture Online(tm). He described his situation this way: "I have corn that was almost drowned in the floods of three weeks ago. There are large areas of yellow corn that is hip high."

By the time the photo on the opening page was taken on July 12, Johnson was convinced he had done the right thing. "It took about 10 days for the corn to get totally green again in the low spots," he says.

Because his fields of commercial corn were further along, he didn't apply any rescue nitrogen to them. "In those fields you can see that the low spots didn't come back to total green again," he says.

Choosing a nitrogen rate is hard enough the first time. It's even harder the second time when you're trying to rescue corn after heavy rains have stolen part of the first application. At that point, it's hard to determine how much nitrogen was lost, how much is left, and the yield potential of a crop that may be struggling to survive in a wet field.

Other farmers and agronomists throughout the Corn Belt can relate to Johnson's dilemma.

Research has shown that urea can convert to ammonium in less than a week under warm, moist soil conditions. In another week or two under those conditions, ammonium can be converted to nitrate.

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