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The grim face of N loss

Agriculture.com Staff 05/27/2010 @ 4:12pm

If you really want to know how your cornfields look as the growing season winds down, park your pickup and jump in a plane.

It will give you a completely different perspective on your fields. And in years like 2008 and 2009, it may give you a completely different perspective on your approach to managing nitrogen.

University of Missouri agronomist Peter Scharf flew over thousands of Midwest fields last August and drove past thousands more. What he saw was lots of yellow corn and lost opportunity.

Although Missouri growers harvested a near-record 151 bushels per acre last year, Scharf says yields could have been 30 bushels per acre higher if nitrogen losses hadn't been so severe.

"My rule of thumb is that more than 16 inches of rain from April through June (or more than a foot in May and June) will lead to nitrogen deficiency problems in a substantial number of cornfields," says Scharf.

"I estimate that N deficiency reduced Missouri's corn crop in 2009 by about 100 million bushels," he adds. "We could have grown at least 20% more if the crop had not been limited by N deficiency."

The losses were certainly not limited to Missouri. According to Scharf, nearly all of Missouri, Arkansas, Kentucky, and Tennessee, and most of Illinois, southern Indiana, and eastern Kansas had more than 16 inches of rain during April, May, and June.

Scharf thinks Illinois growers lost about 20 bushels per acre due to nitrogen deficiencies, and growers in the affected areas of Indiana lost about 15 bushels.

Scharf bases his estimates on his observations and about 1,500 aerial photographs taken in Missouri, Illinois, and Indiana.

He thinks the seven states mentioned above plus Iowa sacrificed 500 million bushels last year. What's more, he thinks just under 500 million bushels were lost due to nitrogen deficiency in the Midwest in 2008. That's a two-year total of 1 billion bushels!

What can you do about it? One thing you can do is add rescue nitrogen to fields or parts of fields that show nitrogen stress early in the season.

Research indicates corn can still use this additional nitrogen up to, and even a little past, tasseling. This can remediate a lot of the damage. But you have to be prepared to act quickly.

"My firm belief after the last two years is that every producer and every retail organization need to have a plan for making rescue N applications in place before the season starts," says Scharf. "Rescue applications of nitrogen fertilizer can be highly profitable when earlier nitrogen applications have been lost due to wet weather."

The other thing you can do to reduce nitrogen deficiency is to regularly apply nitrogen closer to when the crop needs it.

"Sidedress application of NH3 is virtually loss-proof," says Scharf. "Sidedress application of other forms of N fertilizer also has a very low risk of loss because the time between application and uptake is short."

In experiments near Columbia, Missouri, Scharf says sidedressing had a 44-bushel advantage over preplant nitrogen in 2008 and a 68-bushel advantage in 2009.

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