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How late is too late to sidedress N?

Audrey Kittrell Updated: 06/17/2011 @ 3:15pm Editorial Intern for Successful Farming magazine and Agriculture Online

How and when to apply Nitrogen to your cornfield to maximize yield and profitability are already complicated decisions to make.  But add the volatile weather into the mix, and it is downright perplexing.  Unfortunately, every acre may have different N needs, but research at Purdue University in the Department of Agronomy has suggested there are some critical periods in every crop to do your sidedressing.

Wet field conditions can severely delay plans for sidedress applications.  Peter Scharf, University of Missouri agronomist, said the last few years’ higher-than-average precipitation has been raising concerns about soil health. 

“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 N deficiency problems in a substantial number of cornfields,” he said. 

Most of the Corn Belt is already facing these circumstances, leading to questions as to whether forced later-applied N will impact yield and profit. 

The answer is yes, according to results from a 2010 13-acre field-scale experiment at Purdue—but it can be offset.  

During the experimental planting, all rotational corn plots received an initial 24 lbs N/acre as starter fertilizer.

The emerging corn received 28% urea-ammonium nitrate, sidedressed at either growth stage V7 or V15 at 0, 40, 80, 120, 160 and 200 lbs actual N/acre.  Like is common on many farms, the later-applied N was intended for growth stage V12, but prolonged due to weather and an equipment malfunction.   Application at V7 was done with a traditional knife injection tool bar, whereas a high clearance sprayer with a mounted coulter-injection toolbar was used in the V15 application. 

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