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Is Fall-Applied Nitrogen Still Present?

The pattern of warmer- and wetter-than-usual weather this past winter has changed in recent months, but hopes for a warm, dry, early spring have faded. 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.

“Most Illinois producers waited until soil temperatures had dropped to 50 degrees or below before applying anhydrous ammonia last fall, but soil temperatures didn’t stay down as much as usual. We also got enough rainfall in December to cause concerns about whether nitrogen is still in the soil,” says University of Illinois crop scientist Emerson Nafziger.

Nafziger and Dan Schaefer of the Illinois Fertilizer and Chemical Association sampled soil around the state in winter and early spring to measure the amount of nitrogen that has disappeared from the top two feet of soil as a result of the winter conditions.

A sample of eight fields in Vermilion County showed little change in soil nitrogen between December and February, though there was some loss of nitrate between the January and February samples. The percentage of recovered nitrogen that was in the ammonium form—the form that is safe from immediate loss due to binding with negative charges in the soil—actually went up.

Nafziger also sampled fields in Urbana and Monmouth and found a considerable drop in soil nitrogen between early January and late February in both locations. Using N-Serve® made little difference in the amount of nitrogen recovered or in the percentage of recovered nitrogen that was still in the ammonium form.

N-Serve®, a Dow nitrogen stabilizing product applied with ammonia in the fall, was applied in two neighboring fields in Champaign county. In January, 70 percent of the recovered nitrogen in the field with N-Serve was in the form of ammonium, compared to 53 percent ammonium in the field without N-Serve. By mid-March, 73 percent of the recovered nitrogen in the field with N-Serve was ammonium, compared with only 39 percent in the field without N-Serve.

“We need to be cautious because this is from only a few samples, but in this case it looks like nitrapyrin (the active ingredient in N-Serve) did what it is supposed to do: keep ammonium from converting to nitrate, thereby reducing the amount of nitrogen subject to loss. Whether or not that will make a difference in how much nitrogen is available to the corn crop depends entirely on what sort of weather, soil, and crop conditions we have up to the time nitrogen uptake starts,” Nafziger explains.

Overall, results were mixed across the sites and sampling times, ranging from disappearance of more than half of the nitrogen from the top two feet of soil to only small changes. The percentages of soil nitrogen present as ammonium were lower than expected, which could mean considerable potential for loss if wet weather returns.

“We have little previous experience looking at soil nitrogen from fall to spring, so there’s no reason to panic at this point, or to order more fertilizer to replace what might have disappeared,” Nafziger cautions. “Our best strategy now is to assume that most of the nitrogen we applied last fall is still in the soil, to get the crop planted as conditions allow, and to both monitor the crop and stay tuned as we continue to monitor soil nitrogen up to the time that the crop is taking up nitrogen rapidly.”

Nafziger adds that if warm and dry weather returns, there will be little N loss in the coming months If the opposite happens, producers would still have time to manage nitrogen for good yields while minimizing further loss.

Source: Emerson Nafziger and Lauren Quinn, University of Illinois 

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