Farmers may be getting anxious to get back in their fields to apply anhydrous ammonia, but they’re being urged to wait until soil temperatures are much colder.
John Sawyer is a professor and extension specialist in soil fertility and nutrient management at Iowa State University.
“We’ve had a very good harvest going on and people want to continue to do field work, but this is one that they just need to wait for temperatures to get cold,” Sawyer said.
Waiting for cooler soil temps before applying anhydrous ammonia in the fall will better protect the environment and ensure the fertilizer is available to the crop next spring.
“When soils are cold, biological activity is slowed. The conversion of ammonium to nitrate slows greatly, so you have less nitrate formed in the fall and that’s going to benefit…keeping that applied nitrogen in the soil system and reducing loss to water systems,” Sawyer said. ISU Extension and Outreach maintains a statewide soil temperature data map on their website that farmers can use to determine when fall applications are appropriate. It shows soil temperatures this week range from the upper 50s to the upper 60s across the state.
The general recommendation for applying anhydrous ammonia is to wait until soil temps remain below 50 degrees. “Everybody talks about the 50 degrees soil temperature, but that can be a bit of a fooler because we can have a warm up and soil temperatures can go back up above 50,” Sawyer said. “We always like to say 50 degrees and continued cooling and the colder, the better.”
In addition to waiting for cooler soil temperatures, farmers should also make sure that the soil is not too dry, too hard, or too wet. According to Sawyer, those conditions can cause injection issues and allow ammonia to move to the soil surface and be lost to the air.