JEFFERSON CITY, Mo. (DTN) -- They say good things come to those who wait. And if you're presently waiting to make your fall applications of anhydrous ammonia, that's probably a good thing.

While there have been reports of rigs rolling, as a rule of thumb, anhydrous shouldn't be applied until soil temperatures are less than 50 degrees Fahrenheit at a depth of 4 inches. In some regions, it's recommended waiting until the soil temperature drops below 40 degrees. The reason is simple: You still want that nitrogen to stay where you put it.

When anhydrous is knifed into the soil, the ammonia gas reacts with moisture and is converted to ammonium, which binds to clay and organic matter in the soil. Ammonium doesn't move readily in the soil.

However, at soil temperatures above freezing, nitrification happens as soil microbes convert ammonium into nitrate. This form of nitrogen doesn't bind to soil and is highly soluble, which means leaching can occur.

In portions of the upper Midwest, soil temperatures have fallen below 50 degrees. However, according to data from Iowa State University, soils across much of that state have still been hovering around or above the 50-degree mark this week. In Illinois, soil temps on Nov. 6 varied from 47 degrees in the north to 60 degrees in the south, as reported by the Illinois State Water Survey.

According to DTN Ag Meteorologist John Baranick, the low temperatures that are forecast for this weekend and into the beginning of next week will accelerate the downward trend in soil temperatures.

"It's going to be harder and hard for these soil temperatures to stay up going forward," he said. "At this point in the year, the low sun angle is a big factor. The solar minimum (winter solstice) is only six weeks away, so there's not a lot of solar input anymore."

Baranick said it will be difficult for soils across the north to rebound in temperature as they have reached the tipping point. For areas from Kansas through the Ohio Valley and farther south, a drop in soil temperature below 50 degrees should occur during the next few weeks. He noted there's a burst of warmth moving back in next week that is forecast to stick around for a lot of country east of the Rocky Mountains through the end of November.

In a recent Agronomy eUpdate, Kansas State University offered some guidelines when fall-applying anhydrous:

-- On silt loam or heavier-textured soils, wait until soil temperatures at the 4-inch depth are below 50 degrees.

-- Use a nitrification inhibitor with anhydrous.

-- When soils are dry, deeper injection depths from 6 to 8 inches, wing sealers and closing disks can help mitigate application problems.

-- Don't apply anhydrous in the fall on sandy soils.

According to DTN's weekly fertilizer trends, anhydrous ammonia was at $843 per ton this week, roughly 20% higher than one year ago. If you're paying that kind of price, you probably want that nitrogen to stay where you put it. Waiting for lower soil temperatures will help do just that.

Read Baranick's latest Ag Weather Forum here: https://www.dtnpf.com/…

Read this week's DTN Retail Fertilizer Trends summary here: https://www.dtnpf.com/…

You can read the entire K-State article here: https://eupdate.agronomy.ksu.edu/…

Jason Jenkins can be reached at jason.jenkins@dtn.com

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