Soil Temps Still Too Warm to Apply Anhydrous Ammonia


October 23rd, 2012 by Ric Hanson

As air temperatures continue to fluctuate, so do soil temperatures, and that means it is still too early for Iowa farmers to apply anhydrous ammonia (NH3) to their cropland this fall, according to USDA’s Natural Resources Conservation Service (NRCS). Anhydrous ammonia applied before daily soil temperatures, at a 4-inch depth, are 50 degrees Fahrenheit and trending lower can result in nitrogen losses that can impact crop development. These nitrogen losses can leach into groundwater and streams once anhydrous ammonia is converted to nitrate, creating water quality concerns.

As of Oct. 23rd, soil temperatures were actually trending higher across Iowa after air temperatures approached 80 degrees during a 3-day stretch. Historically, soil temperatures at a 4-inch depth cool below 50 degrees in the northern third of the state during the first week of November. In central and southern Iowa, soil temperatures cool below 50 degrees during the second and third weeks of November, according to Iowa State University Extension.

Barb Stewart, state agronomist with NRCS in Iowa, says this year’s drought left residual nitrate in the soil. “In many cases, crops did not uptake all nitrogen applied,” she said. “Consider taking a late spring soil nitrate test next year and make adjustments accordingly to make the best use of the nutrients.” Producers and fertilizer dealers are encouraged to visit the Nitrogen and Phosphorus Knowledge web page,, to view daily, previous day, and a 3-day history of average soil temperatures in every Iowa county.