URBANA, Ill. — The last couple months of torrential rain has farmers concerned about nitrogen loss, noted Emerson Nafziger, University of Illinois extension crop production specialist.

 

“With a lot of nitrogen fertilizer applied early, and with rainfall totaling 5 inches or more over most of Illinois in the two weeks before May 10, many people are worried about nitrogen loss and the possible need to apply more nitrogen than planned,” he said.

The heavy rains of late April and early May have paused and the weather has warmed enough to allow corn and soybean planting (or replanting) to resume – except in the low spots in some places. “Although we wish the weather had stayed warm, the return of cooler weather along with the rainfall did slow nitrification – the conversion of ammonium to nitrate – slightly, and also slowed the denitrification process,” he explained.

Nafziger said both nitrification and denitrification are biological processes, which are faster at higher temperatures. “We know from finding nitrate in the soil that there has been a lot of nitrification,” he said. “Denitrification requires both saturated soils and warm soils, so there has been much less of it, mostly in soils where water stood.”

Clarke McGrath, on-farm research and extension coordinator at Iowa State University’s Iowa Soybean Research Center in Harlan, said the cooler weather has likely slowed down nitrogen losses to a degree, “although it is hard to say how much, so this is helpful for us in many respects.

“On the other hand, the cool soils  and the subsequent slower conversion of fertilizer and release of soil nitrogen is a big contributor to a lot of this ugly, yellow corn,” he said. “The good  news is that with the warmer temperaturesand our corn close to – or at a point where the nodal root system can take off – we should start to see rapid growth and a lot deeper green from here on out.”

McGrath said there has been such a run on replanting corn, that in some areas soybean planting has been somewhat delayed. “The excess rainfall also slowed down our progress planting beans, and in my part of the world (roughly one-fourth of southwestern Iowa), we are just now wrapping up bean planting.

“In between scattered storms before, during and after Memorial Day Weekend, we saw a lot of the last 20 percent or so of bean acres get planted, so we haven’t faced many replant decisions yet,” he added.

Unfortunately, that hasn’t been the case in other parts of Iowa and the Midwest. “If this wasn’t the biggest year for corn replant in history, it had to be a strongsecond,” he said. “We won’t know for sure for a while, since all the numbers aren’t in and seed returns aren’t done, but there was a lot of corn replanted in areas.

“With most of that either replanted, taking prevented planting or converting to soybeans over the last week or two, the focus was on either planting beans the first time or replanted where stands were wiped out by excess rains, diseases, in a few cases, some herbicide injuries; in a lot of cases, a combination of two or three of these or other factors.” 

 

Ben Hushon, general manager of The Mill in Bel Air, Md., said the first challenge weather can present to nitrogen applications is preventing farmers from getting into the field to make pre-plant, topdress or sidedress applications.

“Because it’s ideal to apply nitrogen when the plant needs it, we support split applications, following a pre-plant application with one or two applications during the growing season,” he explained. “Sometimes this can cause challenges. If weather prevents you from making the last application, your crop is left short of the nitrogen it needs.”

Darin Lickfeldt, senior technical development manager at Verdesian Life Sciences in Cary, N.C., said farmers should take steps to protect their applied nitrogen from loss to the elements.

“If it ends up being dry, farmers could lose their applied nitrogen to volatilization,” he pointed out. “If it ends up wet, you could lose nitrogen to denitrification; and if you have water moving through the soil, you could lose nitrogen to leaching.”

McGrath said depending on the region of the state and the weather, “expect to see a lot of NH3 or UAN bars in the fields, and a lot of high clearance rigs with spreader boxes running.

“If the weather doesn’t cooperate, some sidedress acres end up being applied with helicopters or airplanes,” he said. “Typically (it’s) not our preferred plan, but we’ve had to do it in cases where we really needed the supplemental nitrogen.”

As long as soil conditions remain favorable, Nafziger said, “A crop provided with normal amounts of fertilizer nitrogen almost never runs out of nitrogen during vegetative development – at least to the extent that we can see it. This year will be no exception.”