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NRCS 

Technical Note TX-PM-11-05

United States Department of Agriculture

Natural Resources Conservation Service

Technical Note No: TX-PM-11-05

July 01, 2011

Broadcast Sprayer Calibration and Application

Plant Materials Tech Note

Introduction

The use of properly calibrated spray equipment is critical to ensure the protection of the environment, the 

crop and the applicator and to meet the desired goals of the application. Applying too little chemical will

provide inadequate control of target pests and contributes to the buildup of resistant organisms. Applying 

too much chemical can be harmful to off-target species, damage the crop, and poses unnecessary health 

risks and expense for the applicator. Studies have shown that up to 60% of applicators miss the desired 

application rate by 10% or more, 4 out of 5 sprayers checked during the study were not calibrated, and 

one out of every three applicators made errors mixing chemicals (NDSU). 

Calibration Procedures

Calibrating a sprayer helps to determine the exact amount of chemical that will be applied over a know 

distance. This may seem like a daunting task, but can be quite simple. There are many ways to calibrate 

a boom sprayer. The easiest is based on the relationship of 128 ounces in a gallon, and spraying 1/128th

of an acre per nozzle. 

With this method, the 

ounces caught during 

calibration translate 

directly to gallons per acre. 

Table 1, courtesy of Ohio 

State University Extension,

simplifies this method 

even further. Simply 

measure the distance 

between the nozzles on the 

boom and find the 

corresponding spacing on 

the chart. Next, look at the 

“travel distance” column directly adjacent to the nozzle distance on the chart. This indicates the distance 

that should be covered to spray 1/128th of an acre per nozzle. Mark this distance off in the field, and 

record the time it takes to travel with the spray vehicle at the speed used to make applications. It is 

important to time the distance in the field on similar terrain as speeds may change depending on ground 

conditions. Record the travel time 3 times and then take the average. It is imperative to use some form 

Table 1. Calibration distance for each nozzle to spray 1/128 acre.

Nozzle 

spacing (in.)

Travel

distance (ft.) Nozzle spacing (in.) Traveldistance (ft.)

18 227 30 136

20 204 32 127

22 185 34 120

24 170 36 113

26 157 38 107

28 146 40 102

*table and additional information may be found at http://ohioline.osu.edu/aex-fact/0520.html
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Technical Note TX-PM-11-05

of cruise control or to pick a gear and RPM setting to use when spraying. This maintains a constant 

ground speed. Vehicles that cannot travel at a constant rate, such as ATVs, cannot be accurately 

calibrated. It is also important to be up to speed before crossing the first marker when timing the travel 

distance. Back up from the first flag 20 or so yards, and make sure the tractor is at spraying speed before 

crossing the first marker and starting the stop watch. 

Now that the travel time has been established, you are ready to calibrate. Fill the tank with clean water. 

Check all the nozzles and clean all the screens. When complete, turn the sprayer on and let it run. Note 

the fan pattern of each nozzle and look for any irregularities that might indicate a worn or clogged nozzle. 

Replace any damaged nozzles. When complete, turn the sprayer on again. It is important that the sprayer 

be running at the same RPM and operating pressure as when making the actual application. Catch the 

water from one nozzle for the same amount of time it took to travel the distance marked in the field. The 

volume in ounces represents gallons per acre. If 15 ounces were caught, the sprayer is applying 15 

gallons per acre. This should be done for each nozzle. Any nozzle with an output greater than 10% of the 

average nozzle output should be replaced. 

Application

Once the application rate of the equipment is known, it is possible to mix and apply rates of chemical 

accurately. The applicator determines the amount of acreage to be treated, and multiplies it by the 

calibrated rate. For example, if the applicator needed to treat 10 acres, and the sprayer was calibrated at 

15 gallons per acre, the applicator would need 150 gallons of total volume in the tank. Always remember 

that some losses occur while starting, stopping, and turning in the field. Always figure an additional 10 –

15% of total volume to compensate for these losses. This will prevent the applicator from running out of 

spray before completing the task. 

Mixing Chemicals

*Read the label and follow all instructions, it’s the law.

The sentence above cannot be over emphasized. Always wear the personal protective equipment required 

by the label, and follow all instructions. Typically it is best to fill the sprayer’s tank half way, add the 

correct volume of chemical, and then fill the tank to the total desired volume. This helps mix the 

chemical in the tank. The volume of chemical added to the tank should be used to figure the total volume 

needed to complete the treatment. All labels will have warning signal words. Caution means the 

chemical is slightly toxic or causes slight eye and skin irritation. An ounce to more than a pint taken by 

mouth could kill an average-sized adult. Warning means the product is moderately toxic or causes 

moderate eye and skin irritation. A teaspoon to tablespoon taken by mouth could kill an average-sized 

adult. Danger means the chemical is highly toxic or could cause severe eye and skin burning. Chemicals 

in this category carry the skull and cross bones symbol and the word POISON printed in red. A minute 

amount is all that is necessary to kill an average-sized adult when taken by mouth, and skin contact or 

vapor inhalation could cause acute illness (Stevenson 1991). 

The label provides all the information necessary to use the product safely; such as rates for use based on 

the pest controlled, geographic region, soil type, and desired length of control. Some chemicals call for 

the addition of an adjuvant such as crop oil or a surfactant. These will increase the effectiveness of the 
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Technical Note TX-PM-11-05

chemical and should not be ignored. The label will also provide a list of compatible chemicals, if they 

exist, that may be used as mixes, and gives specific instructions for mixing them. Always follow these 

instructions. Adverse chemical reaction can occur if tank mixes are not made properly. 

Rate information is usually listed in quarts, pints, or 

ounces per acre. A good conversion website is a 

handy tool to make rapid calculations. Examples of 

such websites include: http://www.metricconversions.org/volume-conversion.htm and 

http://www.curezone.com/conversions.asp. Table 2 is 

a quick reference for some of the more common units 

used when measuring pesticides.

Spraying

Now that the tank is mixed, the application can 

be made. There are a few things to note when 

applying chemicals. High temperatures, low 

humidity, wind, and temperature inversions all 

play a role in the transport of chemicals off the 

target area. The applicator is responsible for 

any injury or damage caused by pesticide drift

(Stevenson 1991). High temperatures and 

low humidity increase evaporation rates, high 

winds can cause spray to drift, and temperature inversions cause chemical vapors to hover near the 

ground surface and be transported off location. Inversions occur as fog or smoke that hangs in the

atmosphere just above ground level, instead of drifting or rising upward. They occur when air near the 

ground is cooler than the air above it. Avoid making applications when sensitive crops or areas are

downwind of the application site. Early morning and late evening are usually the best times to apply 

chemicals, as temperatures and wind velocities are usually lower. 

The applicator should have the spray boom set at a height, usually around 18 inches, such that the spray 

pattern from the nozzles over lap to ensure complete coverage. The tank pressure and ground speed used 

to make the application should be the exact same used to calibrate the sprayer. Always allow the boom to 

overlap between passes made through the field to avoid leaving small, untreated strips. If nozzles and 

booms do not overlap during application, herbicide will leave a striping effect and weeds which can 

reseed. If the applicator runs short of chemical or has significant amounts left over applications, the 

equipments calibration should be checked. 

Conclusion 

Pesticide application is an important part of the integrated pest management system. In order to be 

effective, they must be applied at the proper rate. Calibrated equipment is essential in making such 

applications. The process described above is simple and consumes little time and should be done often to 

Table 2. Liquid Measure Conversions

1⁄4 qt 1⁄2 pt 1 cup 8 fl oz

1⁄2 qt 1 pt 2 cups 16 fl oz

1⁄4 gal 1 qt 2 pt 4 cups 32 fl oz

1⁄2 gal 2 qt 4 pt 8 cups 64 fl oz

1 gal 4 qt 8 pt 16 cups 128 fl oz

Early morning application showing proper boom height and nozzle 

pattern
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Technical Note TX-PM-11-05

ensure the equipment is functioning properly. In the end, calibration protects the environment, crop, 

applicator, and saves money. 

References

http://www.noble.org/tools/boom.html

http://www.ag.ndsu.edu/pubs/ageng/machine/ae73-1.htm#introduction

http://www.teejet.com/media/007628e1-9b61-4d14-9a8a-12cb388a4c1b-sprayinsun.jpg