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Fall anhydrous applications and dry soil

By Kriss Nelson - Farm News editor | Nov 2, 2020

Fall anhydrous applications and dry soil



The air temperatures seem to be dropping by the day and along with that so are the soil temperatures, which may bring an influx of anhydrous applicators to the fields.

What should producers consider before those NH3 applications?

“With the ahead of schedule corn and soybean harvest many may start thinking about fall ammonia applications, if that is something they have in their normal program,” said John Sawyer, professor of agronomy at Iowa State University and Iowa State University Extension soil fertility and nutrient management specialist.

If that is the case, Sawyer recommends waiting until the soils are cold and getting colder. Sawyer said it has been a long standing rule that soil temperatures should be 50 degrees at the four-inch depth and conditions should be trending colder.

Dry conditions

Is it too dry for an anhydrous application this year?

According to information provided by Sawyer, even air dried soil contains some moisture, although quite low. Ammonia dissolves readily in water, but it is held or retained in soil by clay or organic matter. The problem with dry soil and low moisture is that soil moisture is needed to temporarily hold the ammonia so it can become attached to clay or organic matter as ammonium.

“Many areas of the state have had a dry summer and now a dry fall,” he said. “However, with anhydrous ammonia, generally, we don’t have a problem with dry soils affecting anhydrous ammonia applications, but, sometimes, if the soil is kind of compacted, running the ammonia knife through the soil and bringing up large chunks to the surface, we can get ammonia loss at application.”

If dry soils are cloddy and do not seal properly, the ammonia can be lost at injection, or seep through the large pores between clods and after application.

If that soil is loose, Sawyer added, even if the soil is dry, it can still hold ammonia without any real problems.

Proper depth of injection and good soil coverage are a must for application into dry soils.

Sawyer recommends the injection depth be at six to eight inches.

“The chances then really decrease for loss,” he said.

Wing sealers immediately above the outlet port on the knife can help close the knife track, limit the size of the retention zone, and reduce vertical movement of ammonia.

Closing disks can reduce ammonia loss by covering up the injection track with soil that traps the ammonia as it moves to the soil surface.

Reducing the application rate or narrowing the knife spacing reduces the concentration of ammonia in each injection band.

“That is just something to watch out for and they need to make sure they are paying attention,” said Sawyer. “If they are getting the loss at application, stop or change something or wait for rainfall.”

How does the applicator know there is loss at application?

Sawyer said if you make an application round in the field, and you can still smell ammonia from that application, then you should make adjustments or wait for better conditions.

“With dry soil, you will know if you are having an issue when you are applying,” he said. “You stop and if smell ammonia, you know you got some losses going on. If you see the white puffing, that’s water vapor, but again, if you have water vapor coming to the surface, you could have ammonia loss. You will know if you have an issue going on when you are making the application.”

Nitrification inhibitors

Sawyer said there are several nitrification inhibitors available on the marketplace.

“It is something that can be used to help slow conversion in the fall,” he said.

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