Anhydrous ammonia is a cost effective nitrogen source, but it also brings application and equipment technology concerns, as noted by Mark Hanna, Ph.D., Iowa State University Extension agricultural engineer.

Hanna, among other topics, talked about three major concerns—variation in amount of anhydrous ammonia applied per toolbar knife, speed of application and depth of application. His presentation was made during the University of Missouri Crop Management Conference on Dec. 18 attended by ag retailers, crop consultants and farmers in Columbia, Mo.

“One take home message I want you to get is that anything beyond the old open chamber manifold is a step up in terms of lowering your variation across those manifold outlet ports and getting better application uniformity,” said Hanna.

The goal is anhydrous ammonia equal application flowing from every line going to toolbar knives so there isn’t over application to a few lines. To have enough nitrogen for the crop across the field, additional anhydrous ammonia is often applied with the extra nitrogen going to waste in those over applied rows.  

“With the price of nitrogen fertilizer today, about 150 acres will pay for the cost of that higher priced manifold. So, it just doesn’t make much sense to stay with the old open chamber style model. If you do use one, at least plumb them so that you get better distribution through the outlet ports,” the Extension engineer said.

What is driving the anhydrous ammonia through the system is tank pressure. “As temperatures go down we get some fairly low tank pressures and sometimes that can give us problems,” Hanna noted. “As the pressure drops in the system, you can get more of that anhydrous ammonia bubbling off as gas, which is what gives you some of the distribution problems.”

Hanna said he is seeing more anhydrous ammonia going on as a custom application service by ag retailers. This has brought attention to ag retailers needing to apply as many acres as fast as possible with the least expense. Large-scale farmers are trying to do the same in covering as many acres as fast as possible.

“It turns out if we can lower that tractor drawbar pull, we can drive a little faster or we can pull a larger toolbar. So, going a little bit shallower is on people’s minds in order to get over more acres,” he said.

The other thoughts are less pull means using a less expensive lower horsepower tractor to do the application.

Hanna noted the six-inch depth application appears to cause fewer concerns than the four-inch depth that has been more common with the search for speed, although four inches is deep enough in most situations. Iowa State University has done research work with anhydrous ammonia application at 4 inch and 6 inch depths—fall and spring.

Spring application and planting right into a shallow application zone is the biggest concern, especially if the seed is planted right into the area where anhydrous ammonia application has occurred or if the ammonia is applied right over the top of the seed row in a sidedress situation. There was not much affect to the crop until there was a shallow injection in the spring right in the row at higher rates of 160 pounds per acre and more. Plant populations “started to tapper off,” he explained. Plants also came up with ammonia burn.

Application a little off to the side of the row is OK. And GPS positioning for planting is a good way to avoid directly over the top of the anhydrous ammonia injection.

Maintaining a reasonable injection depth is important and four inches is as shallow as an injection should be done. It might be better with spring application to go with the deeper depths, too.

Hanna said, “There is some potential damage with shallow placement. You need to be at least aware of that, and it probably occurs more in spring application or with drier soils and with a high application rate in the seed zone.”