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Late Winter Nitrogen Fertilizer Application

The unseasonably warm and dry weather this February has prompted some corn growers to begin applying ammonia, according to University of Illinois crop sciences professor Emerson Nafziger.

“While we don’t often have the option to apply this early due to frozen or wet soils, late February and early March is an acceptable time to apply ammonia, as long as we do it carefully,” Nafziger says. “Compared to fall application, late winter application introduces nitrogen a little closer to the time the crop will need it, so it’s slightly safer. Still, a warm, wet spring will mean a lot of nitrate present when plant uptake kicks in. So using a nitrification inhibitor with ammonia applied now makes sense.”

After application, ammonia converts to ammonium, which attaches to negative charges on soil and organic matter, and does not move in the soil. When soils warm up, bacteria begin to convert ammonium to nitrate, which can hitch a ride with water moving through the soil. In this way, nitrate can end up in tile lines and out of the field. This is why it is important to keep nitrogen in its ammonium form as long as possible.

Nafziger says that soil samples taken after ammonia application last fall are showing that soil nitrogen levels held up well through late January. With little rainfall in February, he expects that is still the case.

“Late January samples showed that a little more than half of the nitrogen we recovered following fall application was in the nitrate form, and that this percentage was a little lower where we used an inhibitor. There is less nitrate now than we found a year ago following warm, wet weather at the end of 2015. Nitrogen should stay in the soil as long as the soils stay cool and the weather does not turn unusually wet.

“Some producers prefer to wait to apply ammonia until closer to the time the crop will need it. Having dry soils now increases the chances of having soils dry enough to allow application later,” Nafziger says. “Fertilizer materials that contain nitrate, like UAN solution or urea, should not be applied this early; their application should be close to or after planting. Applying nitrogen close to the time the crop needs it is one of the best ways to limit the potential for loss of nitrogen.”

For more information on this topic, visit Nafziger’s Bulletin post.

Source: University of Illinois

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