Too Early For Anhydrous Ammonia (NH₃) Application

September 20, 2005

Nitrogen being applied to growing corn in a contoured, no-tilled field in Hardin County. (Photo by Lynn Betts)

Iowa crop producers considering a fall application of anhydrous ammonia (NH₃) are encouraged to be patient and wait for daily soil temperatures to drop.

The U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS) suggests applying anhydrous ammonia only when mid-day soil temperatures, at a 4-inch depth, are below 50 degrees Fahrenheit and trending lower.

Historically, soil temperatures at a 4-inch depth cool below 50 degrees in the northern third of Iowa during the first week of November. In central and southern Iowa, field temperatures cool below 50 degrees during the second and third weeks of November, according to Iowa State University Extension.

“Cooler soil temperatures slow biological activity,” said Steve Brinkman, Nutrient Management Specialist with Iowa NRCS, “allowing nitrogen to stay in the ammonium (NH₄) form longer. Then it has a better chance of being retained in the soil.”

Brinkman said anhydrous ammonia applied in the fall tends to have a higher potential of detection in streams than spring-applied NH₃. “When soil temperatures are too warm, it increases the risk of nitrates polluting groundwater and streams,” he said. “I have already seen people transporting anhydrous ammonia in rural parts of Iowa. If producers are applying NH₃ already, that is not good.”

ISU Extension research indicates lower corn yields can result when anhydrous ammonia is applied in fall versus spring, and crop residue cover can be affected by the tillage action of NH₃ application, dramatically increasing the risk of soil erosion.

Brinkman said applying nitrogen fertilizers closer to planting season is more cost-effective due to lower application rates. “Anhydrous ammonia prices are at an all-time high, resulting in significant input costs,” he said. “Care in managing these costs can greatly affect net returns.”

Producers and fertilizer dealers are encouraged to visit the Nitrogen and Phosphorus Knowledge web page, http://extension.agron.iastate.edu/NPKnowledge/, to view daily average soil temperatures for every county in Iowa.

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Contacts:
Steve Brinkman, Nutrient Management Specialist, USDA-NRCS, 515-323-2243
Barb Stewart, State Agronomist, USDA-NRCS, 515-323-2260
Jason Johnson, Public Affairs Specialist, USDA-NRCS, 515-323-2701

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