Consider Soil in Fall-Applied Ammonia Rates, Illinois Study Says


Fall-applied anhydrous ammonia may not fulfill as much of corn’s nitrogen needs as previously assumed.

According to a new study from the University of Illinois, the effectiveness of the practice depends on the soil.

The study used a “tagged” form of ammonia to determine how much of the nitrogen in corn grain and plant material comes from fertilizer, versus nitrogen supplied naturally by the soil.

“There have been a number of studies to compare yields with fall- versus spring-applied ammonia or other treatments. But our study is different because we are tracing the nitrogen from the fertilizer ammonia into either the grain or the whole corn plant above ground. That's what makes this unique,” says Richard Mulvaney, professor in the Department of Natural Resources and Environmental Sciences at Illinois.

Mulvaney and his graduate student, Kelsey Grieshiem, used a stable isotope of nitrogen, 15N, in formulating the tagged ammonia. They applied it at a typical rate of 200 pounds per acre in mid- to late November in six Illinois fields in 2016 and 2017.

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