Farmers are encouraged to wait until soil temperatures remain below 50º F. before applying anhydrous ammonia (NH3) fertilizer this fall.

With the record early harvest this year, 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 protect the environment.

“With farmers finishing harvest earlier than normal, it is important that they still wait for cooler soil temperatures to apply anhydrous so that there is a better chance the fertilizer stays put and will be available to the crop next spring,” says 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.”

“Historically, soil temperatures at a 4-in. depth cool below 50 degrees in the northern third of the state during the first week of November,” says Elwynn Taylor, ISU Extension and Outreach climatologist. “In central and southern Iowa, soil temperatures cool below 50 degrees during the second week and third weeks of November.”

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

Farmers should also be mindful to pay special attention when applying anhydrous ammonia to very dry soil. Dry soil can hold ammonia, but if it is cloddy and does not seal properly, the ammonia can be lost at injection or seep through the large pores between clods after application.

So farmers and applicators should assure proper depth of injection and good soil coverage when applying into dry soils. If ammonia can still be detected in the air following a round of application in the field, the applicator should make adjustments or wait for better conditions.

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