Nitrogen management is entirely about risk management, especially this year. “There’s an economic risk of wasting money and being seen as environmentally reckless by applying too much N, and a risk of corn yield loss from applying too little,” says Dan Frieberg, president of Premier Crop Systems, LLC, in West Des Moines, Iowa. “But there’s also a risk that’s not talked about much — allowing nitrogen-management decisions to adversely affect other crop-production operations.”

With such wild and crazy weather, when you don’t know if you’ll be facing floods, droughts, both or something in between, how can you decide on a nitrogen (N) management plan? 

Wet years tough for N management

“This was a difficult year for nitrogen management,” says Jeff Vetsch, research scientist at the University of Minnesota’s Southern Research and Outreach Center at Waseca, MN. “Normally, using a nitrogen inhibitor in the fall would save most of the nitrogen for the spring crop, but this spring, we figure we lost as much as half of the fall-applied nitrogen because of the wet April and May.”

 

 

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Peter Kyveryga, senior research associate at the Iowa Soybean Association On-Farm Network, found the same thing surveying data from more than 800 ISA on-farm evaluation fields in Iowa in a wet 2007 and extremely wet 2008 year. Cornstalk nitrate tests taken in those years on corn after soybean fields showed more than half the field areas were N deficient. He also found in the two wet years, the average N-deficient areas were significantly larger for fall anhydrous ammonia, fall manure, and spring-applied UAN than for spring-applied anhydrous ammonia. Fall injected hog manure lost a large percentage of N. The percentage of N-deficient areas was more than twice as large as in a relatively dry year, 2006. Total N rates had no effect on the size of N-deficient areas. The size of N-deficient areas was affected by N form, timing and rainfall.

A number of studies have shown traditional N recommendations based on yield goals have missed the mark because of weather-driven variability in N supply from the soil and losses to leaching, volatilization and denitrification. In seven Corn Belt states, N rate recommendations can be calculated with maximum return and profitable N goals — see the Corn Nitrogen Rate Calculator online.

 

Wet years (red and green bars) had at least twice the N-deficient areas as the dry year (blue bar) consistently across all five categories of N management. (Results are from 800 field trials by the Iowa Soybean Association’s On-Farm Network. The deficiency was measured with cornstalk nitrate tests and aerial imagery.)