Even though parts of Iowa saw snowflakes fly last week, ag experts say the soil is likely still too warm in some areas for farmers to safely apply anhydrous ammonia. Barb Stewart, an agronomist with the USDA’s Natural Resources Conservation Service, says it’s cool now but we also saw very warm weather last week, with highs in the 70s and 80s.

“It takes a while for that soil to cool down,” Stewart says. “We’re really looking at the soil microbiology that’s working and it starts to shut down when the soil temperature starts to get below 50.” Soil temperatures, measured at a four-inch depth, need to be below a certain level for a sustained period of time, otherwise, applying the anhydrous will be a waste of time, money and nitrogen.

“You’re talking about temperatures that remain below 50 degrees for an extended period of time,” Stewart says, “probably a week or more.” If the soil is still too warm at depth, it can result in nitrogen losses that can impact crop development.

The losses can also leach into groundwater and streams once anhydrous ammonia is converted to nitrate, creating water quality concerns. Stewart says this year’s drought left residual nitrate in the soil and in many cases, crops didn’t take up all the nitrogen that was applied. She suggests farmers do a soil nitrate test next spring and make adjustments accordingly.

This website provides county-by-county breakdowns on soil temperatures statewide.