Farmers Reminded to Wait on Fertilizer Application

Farmers are reminded to wait until soil temperatures remain below 50 degrees Fahrenheit before applying anhydrous ammonia (NH3) fertilizer this fall. Harvest is progressing rapidly in many parts of the state and officials with the Iowa Department of Agriculture and Land Stewardship and Iowa State University (ISU) Extension and Outreach said that waiting can help reduce nitrogen loss and better protects the environment.

“It is important that farmers wait for cooler soil temps to apply anhydrous so that there is a better chance the fertilizer stays put and will be available to the crop next spring,” said Bill Northey, Iowa Secretary of Agriculture. “Soil temperatures, like air temperatures, can change quickly so it is important that we wait with applications until soils are likely to remain below 50 degrees.”

ISU Extension and Outreach maintains a statewide real-time soil temperature data map on their website that ag retailers and farmers use to determine when fall N applications are appropriate. The website can be found at http://extension.agron.iastate.edu/NPKnowledge

“The reason for waiting to apply anhydrous ammonia until soils are cold is that nitrification, the process of biological conversion of ammonium to nitrate, occurs at a more rapid rate with warm soils. Since ammonium-N does not leach and is not subject to denitrification, as is nitrate, it is more stable in the soil,” said John Sawyer, professor and extension specialist in soil fertility and nutrient management at Iowa State University.

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 as those conditions can cause injection issues and allow ammonia to move to the soil surface and be lost to the air. If conditions are not suitable, then waiting for better conditions is suggested.

Farmers with questions about timing of fertilizer applications can talk to their local ISU Extension and Outreach field specialist or their ag retailer for more information.

Iowa Dept of Agriculture and Land Stewardship