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Adjusting Nitrogen for this Corn Crop

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Despite the wet weather many think may be causing nitrogen fertilizer to get away from corn plants, it is still far too early to make that decision.

While it seems likely some nitrogen fertilizer has moved out of the upper soil as a result of rainfall this year University of Illinois Agronomist Emerson Nafziger says if soils dry out, the torrential rains stop, the sun shines, and the weather gets warmer things should be all good, “The crop is going to tell us this. If by the middle of June some of the crop has really greened up nicely and some has not, then we might need to think about those that haven’t and determine if enough nitrogen is missing to cause this to take place. My suspicion is we will not see very much of that at all. If we are warm and dry and with sunshine for a week, I think the crop is going to look good in almost every field.”

My suspicion is we will not see very much of that at all. If we are warm and dry and with sunshine for a week, I think the crop is going to look good in almost every field. - Emerson Nafziger

One indication the topsoil hasn’t been stripped clean of nitrogen is the good recovery of green leaf color. Nafziger says, as soils dry out, root systems start to expand and the color will change. He explains the corn crop at this point looks like it does not because of lack of N, but due to cool temperatures and abundant rainfall. While it is premature to revise nitrogen management based on what has happened so far, Nafziger cautions it cannot be ruled out, “I would be very reluctant now to make a decision that we need to go put more nitrogen on, especially if we’ve already put the full amount on. If we still need to side-dress and we add 10, or 15, or 20 pounds I don’t have a problem with that. But I think it is premature to decide so much of the nitrogen is gone that we put out there that we need to go back and plan to put more on at this point.”

The good news is there is still time to make such decisions. The corn crop takes up barely one pound of N per acre for every inch of growth it makes up to about knee-high.

Nitrogen deficiency develops over time, and Nafziger says it is almost always more related to current soil moisture than to the amount nitrogen in the soil. So, if fields aren’t extra wet or extra dry over the next month, this season could still turn out to be much more typical than many now expect.

Is Fall-Applied Nitrogen Still Present

Corn growers are concerned about the amount of fall-applied nitrogen that might have been lost through the winter and how this might change nitrogen management this spring.

The first question that needs to be asked on nitrogen management is simple says University of Illinois Extension Agronomist Emerson Nafziger. You need to know how much nitrogen the crop will need, then how much is naturally available, and finally, how much should be applied.

“Our best estimate, and this is a bit of a floppy number, is the crop will take up about a pound of nitrogen for each bushel it produces. About two-thirds of that is going to be in the grain and removed by harvest of the crop. The other third will be in the residue. Some of this will get back into the soil, some won’t”, says Emerson Nafziger.

The amount of nitrogen needed then is about 1 pound for every bushel expected. If the expected yield is 200 bushels to the acre, then it will need 200 pounds of nitrogen.

Pay attention to this part.

Nafziger wrote in an article for the U of I’s pest management bulletin on April 18th that the more productive soils in Illinois contain about 3.5% organic matter. A rule of thumb calculation, read it online in The Bulletin, puts the N from this organic matter at 140 pounds. In some years this is apparently all available to the crop, and in others it isn’t.

The N Rate Calculator, which you may find online, tries to average out the low and high organic N years. N added as fertilizer for corn following soybeans in southern and central Illinois should be about 170 pounds, 20 pounds less in northern Illinois.

As for nitrogen loss, Nafziger has this to say in The Bulletin as it relates to his recent nitrogen treatment studies, “ these results show both the risk of N loss and the benefit from delaying some of the N or using inhibitors may be a little less than we’ve thought. Getting data from another year or two will help paint the picture more fully, but these results give some reason to be confident that the N management systems in common use all have good potential to provide the crop with N. Adding costs by changing N management, for example by making another trip over the field to apply late N, may not provide a positive return compared to applying all of the N in one or two earlier trips.”

Nafziger says the corn crop takes up most of its nitrogen in June.