Jeff Phillips has fielded several questions in the past two weeks about whether it's OK to apply anhydrous ammonia or not. The Tippecanoe County Ag Extension educator breaks it down into two parts. First, consider whether soils are cool enough to prevent losses. Second, decide whether soils are so dry that you can't get good sealing and do a good job of application.
When rubber meets the road and it was his money on the line, Phillips says he would wait, primarily because soils are so dry and he's concerned about sealing and retention of anhydrous ammonia once applied. Applying in the fall is recognized as the most inefficient means of application anyway, although it's a matter or time and convenience for some with lots of acres to cover. If you're applying in the fall, most experts recommend adding N-Serve, a nitrification inhibitor, to help prevent soil losses if normal soil moisture ore excess soil moisture returns either over winter or into spring.
Soil temperature is an interesting question, the Extension specialist observes. As soon as the daytime temperature dropped below 50 degrees F, he heard from farmers saying it was now cool enough- they were going to start. The 50 degree level is generally thought to be cool enough to prevent excessive losses because soils are too warm.
However, that's the rub, the educator says. Just because air temperatures have dropped below 50 degrees doesn't mean soil temperatures have dropped to that level or below. In some cases they have, he notes. But there's usually a lag time between when air temperatures drop below 50 degrees and when soil temperatures decline to that level. Soil is a good insulator.
The other question is whether it will stay cool. Predictions for this week, for example, call for a warming trend. If temperatures would happen to return to higher levels and stay there for any length of time, there could again be a concern over whether some ammonia might be lost that was applied.
His best advice is to check soil temperatures, watch forecasts, weigh how much workload you have for fall vs. spring, and make your own decisions. Purdue University recommendations advise against applying anhydrous ammonia south of U.S. 40, or approximately Interstate 70, because soils in that part of the state generally don't stay cool enough all winter long to avoid losses at some point.