March 28, 2024

Research-based nitrogen recommendations

SPRINGFIELD, Ill. — The Illinois Nutrient Research and Education Council offers recommendations for best management practices based upon nine years of NREC-funded research. The research was conducted — and will continue to be conducted — on actual farmers’ tile-drained fields.

“Tile-drained fields are essential in the research because tile load has been identified as the primary source of nutrient loss to the waterways and environment,” said Julie Hewitt, NREC’s executive director.

The following BMPs follow both the Illinois Nutrient Loss Reduction Strategy and the University of Illinois researchers’ recommendations:

• Use the right nitrogen rate and do not apply the full rate in the fall. NREC recommends saving 30% to 40% of the rate to be applied next year’s pre-plant or sidedress. This helps to manage both environmental and agronomic risk since farmers will not know what the weather will be over the next six months.

The Illinois Nitrogen Rate Calculator is updated each year with the results of dozens of nitrogen rate trials performed throughout the state. The current recommended rates for corn following soybean are:

Northern Illinois: 171 to 194 pounds per acre.

Central Illinois: 181 to 200 pounds per acre.

Southern Illinois: 200 to 225 pounds per acre; nitrogen should not be fall-applied in southern Illinois.

• Wait until mid-day soil temperatures in bare soil at the 4-inch depth is 50 degrees and the weather forecast indicates temperatures will not rebound, but rather will continue to cool. While the Illinois Fertilizer and Chemical Association will post the State Water Survey soil temperature each day, it is recommended growers take the soil temperature themselves.

• Use a U.S. Environmental Protection Agency-labeled nitrification inhibitor with all fall-applied ammonia — N-Serv and Centuro. These products are registered as pesticides because they inhibit bacterial activity that can convert ammonium to nitrate. These bacteria are active until the soil freezes.

The inhibitor is intended to provide protection against nitrification in the late fall, early winter and spring. Protecting ammonia with a nitrification inhibitor helps, but is less effective if soils remain warm.

“There is a lot of anxiety around nitrogen cost and availability, so farmers are tempted to get that fall nitrogen in the ground even if the soil temperature is a little too warm. However, even with the inhibitor, nitrogen is lost to nitrification and loses money for the farmers when soil remains at 50 degrees or above. It is only when soil temperatures are at freezing that the nitrification process stops and keeps the nitrogen in place until spring,” said Shani Golovay, NREC’s research manager.

Lowell Gentry from the U of I added that “timing of fertilizer N is important in that fall N is definitely leakier and that 7% of fall fertilizer N lost to tile accounts for more than 30% of the tile load.”

Gentry further suggested that in a warm winter and spring, farmers need to include a cover crop in their production strategy.

NREC-funded research shows that there is no yield penalty for applying N in the fall, but there is a water quality penalty especially in tile-drained fields. NREC research shows that fall applied N loses up to 12 pounds more per acre than N applied in the spring.

NREC publishes research results on its website at www.illinoisnrec.org.