Next Step in Precision Application

December 12, 2008 06:00 PM
Equipping his operation's strip-till applicator with automatic section control and a more accurate metering system will pay off in fertilizer savings, believes Wade Mitchell.With the prices for anhydrous ammonia, phosphate and potash all hovering around $1,000 a ton, Clay Mitchell and his father, Wade, from Buckingham, Iowa, are glad they installed automated section controls on their strip-till fertilizer applicator last winter.

"If you're getting 5% to 10% overlap, you're wasting some real money,” Clay explains. The Mitchells believe they have obtained that range of savings by installing automated section controls and a RTK auto-guidance system (real-time kinematics with sub-inch repeatable accuracy) on their planter and sprayer.

But the Mitchells weren't satisfied with merely eliminating fertilizer overlap. They also wanted the most accurate metering system on their planter that they could devise.

Soil testing in the row revealed that their soil phosphorus levels varied from 9 parts per million (ppm) to 47 ppm. "Our applicator was putting out fertilizer in pulses, or spurts, from each flute from the metering roll,” Clay says.
The Mitchells don't know how much that affects yield. But they know they want every corn plant to have an equal chance to obtain nutrients.

Section controls. The Mitchells apply dry phosphate and potash fertilizer and anhydrous ammonia as they strip-till, using a modified B&H 9800 Zone Fortifier air-delivery system and Orthman 1-tRIPr strip-till toolbar.
To set up automated section control, they used technology similar to that on their sprayer and planter. A Topcon controller activates Tru Count air-actuated clutches to turn three-row sections of the 12-row dry fertilizer applicator on and off.

At the same time, the controller turns the same three rows of the anhydrous ammonia applicator on or off.
Gemini pneumatic actuator valves are on every row of the ammonia applicator.
On the anhydrous ammonia applicator, the controller uses three-way ARO fluid power valves (made by Ingersoll Rand) to drive the Gemini pneumatic actuator valves that are installed on every row. "Shutoff is almost instantaneous, and there's no bleeding of ammonia,” Clay says.

"We mounted the Gemini shutoff valves on the toolbar, rather than on the knives, to protect them,” Clay explains. "Each knife has its own pressure gauge to ensure that each valve is opening and closing all of the way.”

Setting up the ammonia system required installing a hydrostatic relief valve (or pressure relief valve) at three separate points: between the shutoff valve on the toolbar and the main shutoff control valve; between the main shutoff valve and the manual safety shutoff valve; and between the manual safety shutoff valve and the breakaway coupler.
Tru Count air-actuated clutches control the three-row sections of the Mitchells' 12-row dry fertilizer applicator.
To make their dry fertilizer application as precise as possible, the Mitchells also designed new metering rolls. They used Morris Industries spiral fluted metering wheels and shafts, made from heavy-gauge stainless steel, inside housings that Wade fabricated.

"They provide a steady stream of fertilizer, even at low speeds, which is what we were looking for,” Wade says.

The automated section control and new metering system are the latest step in a quest for perfection that began in 2000, when the Mitchells adopted RTK GPS auto-guidance. Since then, they have added automated nozzle and row-unit controls, RTK implement guidance, controlled traffic and strip-intercropping of corn and soybeans.

"We figure if we're not doing the very best we can, we need to change something,” Wade says.

For More Information

To learn more about the products mentioned in the story, visit:
-Tru Count:
-Gemini valves:
-Morris Industries:
-Aro/Ingersoll Rand:

With items found on the farm, Wade Mitchell (on ladder) and employee Robbie Merkle check the accuracy of anhydrous ammonia knives.Checking Knives is the Key to Accuracy
Even with a state-of-the-art applicator, some plants can be shortchanged on nutrients—and fertilizer wasted—if ammonia knives don't deliver a uniform flow. A simple, but important, test can prevent that from happening.

"We test new knives before we install them on our toolbar,” says Clay Mitchell, who farms with his father, Wade, in Buckingham, Iowa. "We have found some of them too far out of spec to be usable.”

The test requires a stepladder, a funnel, tubing, a 5-gal. bucket and a water bottle. Fix the funnel to the stepladder and clamp a knife in a vise so both maintain a constant height from knife to knife. Connect the funnel to the fertilizer tube on a knife, and pour a measured amount of water through it. "Use a water bottle, rather than a hose from a faucet, because pressure from the faucet could vary,” Wade says.

Repeat the process three times for each knife, and calculate the average amount of time for the water to run through. Look for differences in the amount of time it takes. "If it takes 14 seconds with one knife and 10.3 seconds with another, one row is getting 36% more fertilizer,” Wade ex-plains (14 – 10.3 = 3.7, or 36% of the smaller number.)

"Sometimes we find tubes are plugged or they haven't been completely pinched off at the end, so ammonia comes out both holes,” Wade says. "Sometimes differences result from the amount of penetration when the tube was welded onto the knife.”

Another way to test knives is to set each knife in a bucket of water and turn on the applicator. Run the applicator until the water is about saturated, before ammonia is released as a gas, and weigh the buckets. "You have to do this test outside,” Wade says. "The other test works well when you're servicing during the winter.”

With their dry fertilizer applicator, the Mitchells set a bucket under each row unit, run the applicator for a while and then weigh the buckets. With current fertilizer prices, calibrating applicators is very important, they say.

You can e-mail Darrell Smith at

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