1. Watch the temperature.“Our guideline is, when it hits 50°F. between 6 a.m. and 8 a.m. at the 4-inch depth, it’s time to apply,” says Dave Franzen, North Dakota State University Extension soil specialist.
Applying anhydrous ammonia before soil temperatures reach 50°F. can lead to ammonium conversion to nitrite, says John Sawyer, Iowa State University Extension soil fertility specialist. He recommends spring N applications and sidedressing instead of fall applications to avoid loss.
2. Consider the soil type.“Soils that have a greater chance for N loss would be less preferred for fall applications,” says Sawyer. Also, avoid applying N in the fall on historically wet fields.
3. Plan split applications.
Franzen recommends applying half of the total N rate in the fall or preplant, and then the other half when the corn reaches V5 to V8.
“That way, if it does become really wet in May and early June, you only have half of your N at risk,” Franzen explains.
4. Use the correct form.
Only certain types of N fertilizer should be fall applied. For fall applications in Iowa, Sawyer only recommends anhydrous ammonia. All other forms should be spring-applied he says.
“Some states don’t recommend putting on urea at all, but we haven’t found that to be an issue,” says Franzen. However, he doesn’t recommend UAN for fall applications.
5. Follow the guidelines. Franzen recommends checking state guidelines before making N applications. State guidelines will give combinations recommendations for fall N applications, he says.
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