Soil temperatures should be 50 degrees or cooler four inches down before applying fall nitrogen. Rebecca Ahlers, Iowa State University Extension and Outreach Field Agronomist, says waiting for soil temperatures to remain below 50 degrees is important in getting the most out of the nitrogen being applied. She explains the nitrification process converting ammonium to nitrate slows down with cooler temperatures, whether it is anhydrous ammonia or manure.

Soil temperatures in Washington County Friday were 53 degrees, and dropped to 49 degrees Saturday and 46 Sunday. For a map of soil temperatures across Iowa click here.