Taking time to calibrate your sprayer before heading to the field could cut herbicide costs by as much as 30%.

That's according to Erdal Ozkan, an Ohio State University extension ag engineer.

Plus, calibrating helps protect the environment - because then you know exactly how much herbicide is used, Ozkan says.

Just looking at the sprayer or putting on new nozzles is not enough. A recent Nebraska survey found that only one in three sprayer operators apply within 5% of the estimated rate.

While there are several ways to calibrate a sprayer, Ozkan finds the ounce calibration method the quickest and easiest.

"With this method, it works out nicely because average ounces collected from the nozzles correspond to gallons per acre."

The method simulates exactly what you'll do while spraying - before you make mistakes in the field, he adds.

You'll need a measuring tape, a watch indicating seconds and a measuring jar graduated in ounces. The process takes half an hour, and there are no calculations required. If you don't have someone to help you, pick out fence posts or other markings.

"That could be your calibration area for many, many years," Ozkan points out. Ohio State, as well as other universities and spraying companies, offer credit-card size instructions to carry in your wallet. Or, use the following guidelines:

1) Look at the chart to find out the distance to drive in the field. For boom sprayers, use the nozzle spacing. Use row spacing for directed and band rigs.

For example, if the nozzles are spaced 20" apart, drive 204'. Measure travel distance in a level field. Many tractors and sprayers can gain or lose more than 10% of the desired speed while they move up and down slopes. Mark the distance with flags.

2) With water in the tank, travel at normal spraying speed, operating all of the equipment. Count the seconds required to drive the measured distance.

3) With the pump running, collect water for the amount of seconds in Step 2. Use a container marked in ounces. If using a boom, catch the spray from one nozzle during the noted time. With directed rigs, collect the water from all nozzles per row for the specified time.

The average sample collected from the nozzle or nozzle group in ounces is equal to gallons-per-acre applied by the entire sprayer. Compare the actual application rate with the recommended rate. If the actual rate is more than 5% too high or low, make adjustments.

4) Repeat for each nozzle to assure uniform distribution.

"Knowing the gallons-per-acre actual rate doesn't mean the job is done," Ozkan points out. Uniform application across the boom is as important as getting the right gallonage from the sprayer. He uses a sprayer table (patternator), which visualizes spray patterns.

Farmers can evaluate uniformity using water-sensitive paper strips, which are available from Spraying Systems Co., Wheaton, IL. Lay strips on the ground and make a pass over them, with the boom set at the nozzle manufacturer's recommended height. You can see where the sprayer is over- or underapplying.

Watch the spray pattern of each nozzle. If a single nozzle's discharge isn't within 10% of the average output of all the nozzles, replace it. If more than one nozzle is not satisfactory, replace all the nozzles. After adjustment or correction, recalibrate.