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Fall Anhydrous Ammonia Application Considerations Iowa State University. (September 12, 2002) - Many Iowa producers should start thinking about applying nitrogen (N) in the fall after the crops are harvested to get a head start on spring fieldwork according to John Sawyer, Iowa State University Extension (ISUE) soil fertility specialist. "Producers are encouraged to wait until spring to apply N," said Sawyer. He continued, "But if you plan to apply anhydrous ammonia this fall, wait for average daily soil temperatures to reach 50 degrees Fahrenheit (F) at 4 inches with a forecast of cooling soil temperatures. Cool soil temperatures slow biological activity and the process called nitrification. Nitrification converts ammonium to nitrate. The nitrate form is more susceptible to loss through leaching and denitrification. Slowing nitrification, therefore, helps retain applied nitrogen in the soil." Sawyer added that anhydrous ammonia is the N fertilizer product that should be considered for fall application. Elwynn Taylor, ISUE climatologist says, "Historically, soil temperatures at a 4-inch depth cool below 50 degrees in the northern third of Iowa during the first week of November. Soil temperatures in the central and southern parts of Iowa normally cool below 50 degrees during the second and third weeks of November, respectively." Taylor encourages producers and fertilizer dealers to visit the Nitrogen and Phosphorus Knowledge web page, extension.agron.iastate.edu/NPKnowledge to view daily average soil temperatures for each county in Iowa. The Web page also has a three-day forecast. "You can also take soil temperatures at either 10 AM or 7 PM at a 4-inch depth on flat, bare soil," Taylor said. In the summer of 2000, the Agribusiness Association of Iowa (AAI) compiled a list of management practices for the fall application of anhydrous ammonia. This list became the 2000 Fall Application of Anhydrous Ammonia Policy. "This voluntary policy was based on principles used for many years by the local agronomy centers throughout Iowa," said Chris Murray, AAI Vice President for environmental policy and agronomy issues. The AAI Policy, the Nitrogen and Phosphorus Knowledge web page and local temperature records were distributed to all locations in the state that sell anhydrous ammonia. "The policy did create discussion out in the country, which was just the effect the AAI Board of Directors was looking for," according to Murray. "A survey supported our impression that fewer applications of fall anhydrous ammonia occurred in the fall of 2000. In fact the survey noted that most dealers and producers waited until the soil temperatures reached the 50 degree F level at 4 inches." Comments from the 2000 survey were used to update the policy for 2001. The AAI Board re-affirmed their support for the policy at their June 2002 board meeting. Copies of the 2002 policy can be obtained from AAI by contacting Murray at (515) 262-8323. John Creswell, ISUE nutrient management education project coordinator, encourages producers and fertilizer dealers to visit the ISU Continuing Education and Communication Services Web page (www.extension.iastate.edu/pubs) for a copy of IPM 69A, "Don't Go Until It's 50 degrees F or Below." Producers who decide to wait until this coming spring to apply N can download IPM 67A, "Nitrogen Options: Get the most from each pound of nitrogen!" Contacts: John Creswell Chris Murray John Sawyer Jean McGuire |