DES MOINES — As air temperatures continue to fluctuate this fall, so do soil temperatures. This means it may still be too early to apply anhydrous ammonia (NH3) to cropland without risking nitrogen losses through groundwater leaching.
Anhydrous ammonia applied before soil temperatures, at a 4-inch depth, are 50 degrees Fahrenheit and trending lower will quickly convert to nitrate. While ammonium will mostly stay attached to the soil, nitrate will flow with water.
“If we get more rain than the soil can absorb this fall or next spring, the nitrate is at risk to leach into groundwater, tile water, and streams,” says Eric Hurley, nutrient management specialist with USDA’s Natural Resources Conservation Service in Des Moines.
Nitrogen losses can also impact crop development, says Barb Stewart, state agronomist for NRCS in Iowa. “We encourage farmers to wait until spring to apply fertilizers,” she said. “This not only prevents nitrogen losses throughout the fall and winter, but spring application ensures the nitrogen is available when the crop needs it the most.”
Farmers and fertilizer dealers are encouraged to check Iowa State University Extension's Iowa Soil Temperature Map at extension.agron.iastate.edu/NPKnowledge/ for trending soil temperatures throughout the state.