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Corn+Soybean Digest

Calibrate Carefully

Dave Collins carries a periodontal pick in his shirt pocket every spring.

It's not because he moonlights as a dentist or is overly concerned about his teeth. Collins, a Gothenburg, NE, crop consultant, uses the small plastic pick to scrape dirt or other debris from sprayer nozzles.

Cleaning nozzles carefully is one of several steps he takes with his farmer-customers to get their sprayers calibrated and ready to go.

Proper calibration helps ensure accurate application, Collins says. He works with his clients to calibrate their sprayers every spring.

"We work through it step-by-step and usually get the job done in about 30 minutes."

Before calibrating, it's imperative that growers or custom applicators completely clean their sprayers, he says.

"Generally, a cleaner like Dawn dishwashing soap is adequate. But, if you're using Roundup, more thorough cleaning procedures are necessary," Collins says.

"You can get herbicide damage if you don't use a commercial-grade cleanser on your system, because Roundup will draw old chemical residues out of the tank lining, hoses, etc. I've seen a lot of soybean fields folded up because people just rinsed their sprayers out a couple of times with soap and water."

After thoroughly cleaning the tank, hoses, screens, etc., Collins recommends taking the nozzles off and checking them for wear.

"If I find anything wrong with a sprayer, it's generally where somebody had some plugging trouble with the nozzles the year before and tried to clean it with a pocket knife. That'll screw up the pattern and output of the nozzle. If there is 10% or greater variation in nozzle output, they should be replaced."

Finally, check gauges to make sure they're functioning properly, and inspect pumps and fittings for leakage, Collins says.

Once your cleaning and maintenance work is complete, you're ready to begin calibration.

Bob Klein, University of Nebraska extension cropping systems specialist, recommends the following method:

Step 1: Using the accompanying table (see printed article), select the travel distance according to nozzle spacing on the sprayer. Measure the travel distance in a level field.

The time required to drive that distance will give the speed of the sprayer, so the measured distance and timing must be exact.

Step 2: Drive and time the sprayer in seconds at the throttle setting, pressure setting and load used during spraying. The spray tank should be 1/2-2/3 full. Repeat at least three times and average the results.

Step 3: With the rig stationary, bring the power unit to the throttle setting, and the sprayer to the boom pressure, used in Step 2. Catch the nozzle discharge in a calibration jar for the time recorded in Step 2 and measure it in ounces. For an accurate assessment of the sprayer, measure the discharge from all nozzles and average the results.

Step 4: The measured ounces from a nozzle are equal to the gallons per acre that will be applied.

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