Bill Butler, Sublette, IL, built his own variable-rate ammonia applicator for $6,611. “Since we no-till our beans and do only minor tillage before planting corn, this is all we need,” Butler says. He farms 1,313 acres of corn and beans in northern Illinois.

He's saved 11 tons of anhydrous ammonia annually by adding a pump, cooling tower and Rawson Accu-Plant drive motor to a DMI ammonia applicator to vary its application rate (right). He keeps the ammonia in its liquid state until it enters the individual hoses to the knives by eliminating the vapor at the cooling tower.

Adding a Rawson drive varies his application rate by 32% up or down, although the orifice size limits it to 10% up or down. The orifices at the distribution manifolds are selected to match the target rate and ammonia temperature, which is critical in maintaining the ammonia in its liquid phase as it moves through the system. “Think of this as a variable-rate sprayer,” Butler says, “and you have the basic concept.”

Where he sees the most savings from variable-rate application is his ability to incorporate numerous nitrogen (N)-rate plots. “This information gives me the knowledge (and courage) to lower my rate to levels below that used by many farmers,” Butler says. “How many of us know the optimum N level? With ammonia at $1,000/ton, over-applying by 20 lbs./acre would cost $12/acre — or $12,000 on 1,000 acres of corn.”

He also built a variable-rate DAP applicator (right) by mounting a Rawson Accu-Rate drive on the front of an old fertilizer buggy, along with an oil cooler and reservoir for the fan drive. A low-profile GPS antenna was mounted just to the back of the tractor cab. The tires are 21.5L/16 on 8,000-lb. hubs. He's used it to variable-rate apply more than 50 tons of DAP (18-36-0), and now MAP (11-51-0) due to supply shifts.

Butler converted the spreader fan drive to hydraulic to minimize mechanical drive components, which were prone to rust. All this for $900 plus the Rawson drive, single axles, bigger tires and some shop time.