It used to be that growers who wanted to inject anhydrous ammonia in their fields basically had one option. Knives, fitted with nozzles and closing wheels, dug a furrow in the ground about 6 to 8 in. deep and filled it with fertilizer.

But recently, some manufacturers have introduced an alternative to this called “high-speed, low-draft” (HSLD) applicators that use single-disc coulters instead of knives to place the fertilizer. The new applicators work at a shallower depth, typically 3 to 5 in. Manufacturers that make them say they are about sold out.

“I can’t tell you how many calls I’ve fielded just this week for these coulter-only systems,” says Andy Thompson with Yetter Manufacturing, which makes the 2987 Magnum.

Dawn Equipment, which introduced the 6000 Anhydra applicator last fall, reports similar interest. “High-speed, coulter-only systems are in extremely high demand right now,” says Rodney Arthur, Dawn’s marketing director. “Our manufacturing plant is open 24 hours a day, six days a week, just to keep up with demand.”

The case for coulters

Arthur says these coulter-only anhydrous bars started getting play around 2008, as farmers searched for a faster way to inject the unstable gas of anhydrous ammonia. Because coulters penetrate only the top 3 to 5 in. of soil, they can be pulled as fast as 10 to 12 mph, manufacturers say. Knives, which go deeper, are limited to about 5 to 6 mph.

Makers of these tools cite other advantages, too. They displace less soil than knives, which reduces erosion and helps keep moisture in the ground. When being used for side-dress application, coulter units allow for application at earlier growth stages without the risk of covering the small plants, says Thompson, Yetter’s regional sales manager. And because of their shallow working depth, they have lower draft requirements, which can save on fuel costs.

Like knives, coulter injectors can apply not only anhydrous but liquid and granular formations as well, and, in some cases, manure. And they are designed to work three seasons — fall, before planting, and mid-season once the crop has emerged — so that the same tool can be used year-round.

“In the anhydrous market, disc-style applicators are definitely getting some play,” says Pauley Bradley, nutrient application product manager with John Deere, which makes the 2510H high-speed applicator.

Potential risks?

Despite their popularity, the applicators also have their detractors. Companies that have stayed with the same tried-and-true knife-based toolbar say that unless field conditions are perfect, coulter-only applicators don’t go deep enough for the anhydrous to be sealed in the soil. 

“You can drive around the fields all day and cut nice grooves,” says Rob Zemenchik, Case IH tillage marketing manager for Case IH. “But if the gas doesn’t seal, then we’ve lost money and yield not to mention environmental and safety issues, and that is the rub.”  

He cites a 2005 study conducted by Iowa State University to support his claim. The study measured nitrogen (N) loss from a “prototype” single-disc injector and a conventional knife injector. Researchers reported that NH3 losses during application with the single-disc injector were 3 to 7% in finer-textured soils (clay loam, silty clay loam, and loam) and 21 to 52% in a coarser-textured fine sandy loam soil, indicating the need for better sealing mechanisms. In comparison, applying with a knife injector at deeper depth resulted in losses of 1 to 2% across all soil types.

In a more recent study conducted over three crop seasons (2007 to 2009), crop scientists from the University of Illinois, Iowa State University and Kansas State University found that corn yield between the two systems were similar, except at the highest rate of N (200 lbs. N/acre), where HSLD applicators showed a 11-bu./acre disadvantage.

The testing was done in Iowa, Illinois, and Kansas using a prototype John Deere 2510H high-speed low-draft applicator and a John Deere traditional anhydrous ammonia mole-knife injection applicator. Nutrients were applied at different rates in worst-case scenarios: nitrogen applied over the crop row in no-till soybean stubble.

Researchers reported that the drop in yield was the result of seedling injury for the spring preplant application in 2008 and 2009 in Iowa, and canopy damage by ammonia losses during side-dress application in Kansas in 2009. “Across all site-years, we observed that the TRAD [traditional] system allowed higher rates of application with less N loss compared to the HSLD system,” the researchers state.

Bottom line

Fabian Fernandez, University of Illinois soil fertility scientist who worked on the study, says the bottom line is that shallow placement can work — in other words, allow faster application and less horsepower. But the shallow depth of injection could cause N loss and yield reduction when soil conditions are not near ideal for the application.

Fernandez says that if the soil is wet or too dry, there is a higher risk of N loss because anhydrous ammonia is being applied very close to the surface. Under such conditions, soil is less able to retain the anhydrous ammonia and some can be lost to the atmosphere, he says. The ideal soil condition for ammonia application is 15 to 20% moisture. 

“Farmers need to make sure soil conditions are optimum always, but especially when using HSLD applicators,” he adds. “Also, they need to make sure that the applicator is able to create a good seal once the nitrogen is applied. And, in preplant applications, it is best to try to separate the planting row from the point of anhydrous ammonia application to minimize the chance of seedling injury.”

Recent refinements

The newest coulter-only applicators are designed to address those problems. Manufacturers say that second-generation tools are equipped with better sealing mechanisms such as new and improved closing wheels, sealing plates and adjustable gang angles to minimize fertilizer escapes.

The coulters themselves are now bigger to increase the depth of application. For example, some companies have gone from an 18-in.-dia. blade to a 22-in.-dia. blade. Other changes include better down-pressure systems, more accurate gauge wheels, the addition of row cleaners, and improved wiper wheels to clean off residue.

“We’ve taken extreme measures to ensure that, if conditions are generally favorable, any loss in anhydrous is no more than using a knife,” says John Deere’s Bradley. He says Deere supplied the applicators in the recent study in Illinois, Iowa, and Kansas in order to find the weak spots of its prototype, all of which have been addressed with its new 2510H applicator.

Great Plains has gone to a three-coulter liquid system with its new Nutri-Pro 3000 and 4000 applicators, which went into production in 2011. The middle coulter runs between two row cleaners, and the rear coulters are 8 in. apart. They clean and till a 12- to 14-in. zone. One or all three can apply liquid fertilizer, says Tom Evans, vice president of sales for Great Plains.

“We are using turbo coulters to fluff up the soil and precision place fertilizer. Then, with RTK guidance, plant 4 in. to the side of the fertilizer,” Evans says.

Other companies, like Exactrix and aNH3, have focused on the anhydrous delivery system to reduce losses. They have designed their own pressurized systems that keep anhydrous in its liquid form until it is injected in the ground. As a result, the manufacturers say that the systems are not going away soon.

“As it stands, we feel very confident of our current system,” says Dawn’s Arthur in reference to the new Anhydra 6000. “Provided it is properly configured, it can put down very high rates of multiple products at very high speeds in basically any condition. And with regard to sealing performance, I’ll take on a mole knife any day of the week.”