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Calibration checkup

How good are you at applying the right amount of chemical to your crops?

That's a question posed to farmers in the past couple of years. It's an update of a project conducted in the 1980s called Billion Dollar Blunder. This project, in which Successful Farming magazine funded University of Nebraska research, found that inaccurate chemical application costs U.S. farmers $1 billion a year.

Times are different now. Today's glyphosate-tolerant crops have shaved chemical costs considerably. Still, it's important your sprayer applies the right rate of chemical. The lower rates of today's herbicides have little margin for misapplication.

Accurate application is particularly important when applying contact herbicides like Liberty on corn. Merely injuring a weed by incomplete contact can leave it lingering to grow later in the season.

Ames, Iowa, farmer Jerry Ryerson refers to these as "mad" weeds. "Those that are injured or stressed will come back and get you," he says.

Plus, part of being a good environmental steward is applying no more chemical than is needed.

Today's spray monitors do an excellent job of ensuring accurate application. Still, they aren't foolproof. Something as simple as a loose magnet on a monitor or a plugged nozzle can cause misapplied chemicals.

That's why sprayer calibration is still a good idea. "I had never calibrated before," says Ryerson.

That changed this year when his was one of eight sprayers calibrated under this project by Iowa State University (ISU) Extension agricultural engineers Mark Hanna, Kapil Arora, and Greg Brenneman.

Cooperators first filled their sprayers with water and set the spray monitor with the speed and pressure they would normally use. In Ryerson's case, he plugged in a programmed rate of 60 pounds per square inch (psi) at a 6.5-mph speed.

The cooperators and the ISU agricultural engineers then collected water in containers under each sprayer nozzle for 30 seconds.

The agricultural engineers used readings from each nozzle collection to detect two factors:

  1. How output compared between nozzles across the spray boom. Application accuracy dips when five to 10% of the boom's nozzles vary more than five percent from the average of all tips.
  2. How output of each nozzle compared with manufacturer's recommendations. "If it's just one nozzle that is a problem, just replace that nozzle," says Brenneman.

However, the ISU agricultural engineers recommend replacing all nozzles when 10% to 20% of tips vary five percent or more from manufacturer specifications.

Ryerson normally replaces nozzles every two years on his sprayer. The calibration test showed it was time to replace nozzles again because 6% of his tips exceeded the recommended five-percent variation from boom average. Furthermore, 11% of his tips exceeded the five-percent variation from manufacturer's specifications.

This summer's calibration also prompted another cooperator to replace nozzles before the start of next year's spraying season.

"It was the first time I had ever calibrated in this manner," says Curt Van Wyk, Otley, Iowa. "The biggest thing I discovered was that I had a couple of plugged nozzles."

The ISU agricultural engineers give several tips to remember regarding calibration:

  • Calibrate annually.
    This is particularly true if you cover 1,500 to 2,000 acres or more in a season. This will help tip you off to problems before spraying season starts.
  • Take pressure readings at the boom.
    This will ensure the pressure you set is actually the pressure that is being applied.
  • Calibrate when you have ample time.
    "You may have more time to do this before putting the sprayer away in late summer than you do before planting," says Hanna.
  • Take both boom average and manufacturer specification readings.
    There are times when the boom average reading can mask problems.

For example, in two tests, all tips were within the five-percent boom variance. But 89% and 85% of the tips, respectively, exceeded the five-percent variance from the manufacturer's specifications.

"A spray controller can mask this problem by changing overall system pressure to maintain application rate," says Hanna. "When this happens, the spray operator is unaware of the uneven patterns that develop in individual nozzle tips."

How good are you at applying the right amount of chemical to your crops?

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