Farmers should be careful to monitor soil temperature before applying fall anhydrous ammonia, cautions David Harms, founder of Crop Pro-tech crop consulting, Waverly, IL.

“The soil temperatures aren’t 50° yet [as of last week] and there has been a lot of anhydrous being put down without a nitrogen (N) inhibitor,” he says. “The N loss that results from putting N down too early will require farmers to apply more in the spring, either pre- or post-emergence.”

More N loss often results from a pre-emergence spring application than a post-emergence application, he adds, but the application window for a spring pre-emergence application is wider. Both could be avoided entirely, however, says Harms, by waiting until fall soil temperatures are cool enough to avoid N loss when applying anhydrous ammonia and by using an N-inhibitor, when appropriate.

Applying anhydrous ammonia too early is bad for the environment and the farmer, says Dave Coppess, Heartland Coop, vice-president, sales and marketing and president of Agriculture’s Clean Water Alliance (ACWA). That’s why the “ACWA Fall Nitrogen Code of Practice was adopted back in 1999, when it formed,” he says. “It’s been an ongoing agreement among retailers here that is consistent with guidelines from Iowa State University.”

This code is a formal agreement among fertilizer retailers in the Raccoon River watershed to wait to distribute anhydrous ammonia for fall application until soil temperatures reach 50° F at a depth of 4 in. (60° F with use of an N inhibitor) with a forecast of cooling soil temperatures. “We want to make sure that our fall N applications don’t lead to environmental problems,” says Coppess, “but we also want farmers to get the full value of their dollar for what they are paying for N.”

The Raccoon River watershed reaches from Des Moines up to north-central Iowa, says Coppess. “The Des Moines Water Works draws from the Raccoon River and is responsible for 17% of the water used by consumers in Iowa,” he says. “It was assumed that there was a direct correlation between N spikes that occurred in the public water about the same time farmers were applying N. We’ve learned since that there are many variables leading to water nitrate issues. Soil mineralization and point source contributors represent the higher percentage source of water impairment. Fall-applied fertilizer is actually a very small contributor.”

The ACWA has set up 40 sampling sites along the Raccoon River with certified samplers checking the water from April through October, says Coppess. Last winter, the Agribusiness Association of Iowa (AAI) also adopted the fall N code, he adds.

“We’re now expanding our efforts to the Des Moines watershed,” says Coppess. “We’ve added six more ag retailers as members of ACWA and will begin certified sampling next spring.”

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