Is Your Sprayer Calibrated and Ready for Spring?

April 7, 2021 6:26 AM
Blog Post

As the weather turns warmer and the days grow longer, many of us are thinking about getting equipment like sprayers ready for the spring. Beyond making sure the machine is mechanically sound and fit for spring (which this past blog post can guide you through), we need to make sure it’s calibrated to accurately apply pesticides and fertilizer.

Before calibrating, make sure the machine has been cleaned of any potential pesticide residues and that the tank has only water in it. Always wear proper PPE when calibrating spray equipment as small amounts of pesticides may still be harmful. Make sure you’re doing the calibration in an area where the water from the machine won’t contaminate or runoff causing potential negative environmental impacts.

The first step to proper calibration is to understand how you plan to operate the machine this year. Knowing what speed you plan to spray at, your spray pressure and desired application rate are key to the calibration process. We can use this information to determine what the desired nozzle flow rate should be. This worksheet can help you determine your targeted nozzle flow rate.  Combined with the type of products being applied and desired droplet size, this helps select and install the proper nozzles on the sprayer boom. If spraying fertilizers, it will be necessary to use include the water rate conversation factor in your nozzle sizing calculations. For more information about this conversion, this article from University of Nebraska – Lincoln.

With the proper nozzles installed, perform a nozzle catch test to ensure everything is operating properly. To do this, the machine needs to be set up to spray at the desired operating settings while stationary. The machine should be operated at full engine speed, pressure set to field operating level, and all the boom sections open and spraying. To get the machine to spray while stationary, enter a calibration mode or manually trigger the machine to spray product. Your owner’s manual or equipment/precision ag dealer should be able to help you through this process.

Next, you will need a stopwatch to time the nozzle and a container to catch dispensed water (Figure 1). Measure the water applied out of each nozzle over the course of one minute using the catch container and a stopwatch. Do this for each nozzle on the machine. It is often easier to have a second person helping so they can operate the stopwatch and record the volumes from each nozzle while you hold the container at each nozzle. Once complete, review the values and check for any that are deviating too far from your desired flow rate.

Nozzles that are producing significantly less flow than they should may be plugged. Check and clean these nozzles then retest them to get a new flow rate. A plugged nozzle can impact the flow out of surrounding nozzles as well, so it may be beneficial to check other nearby nozzles again. Any nozzle deviating from the desired flow by more than 10 percent should be replaced. If there are multiple nozzles deviating by 10 percent or more, consider replacing the entire set of nozzles.

Manual calibration setup for sprayers
Figure 1. Before starting the calibration process, be sure you have proper PPE and a stopwatch and container to catch dispensed water, or a nozzle calibration tool. Using a graduated bucket or other container, capture the dispensed water from each nozzle for a defined period of time (typically one minute). Compare these to the target to determine how accurately your machine is applying.

This process should be repeated for each application configuration (combinations of rates, nozzles, pressures, and speeds) you plan to apply at this season. While this can be a time-consuming process, it’s essential to ensuring products are applied according to the label and the best possible efficacy is achieved. To speed up the process, a nozzle calibrating tool can be used. This can be a good tool to keep in the sprayer for quick nozzle flow checks while in the field. In this video we demonstrated how quick and simple using one of these tools can be.

If you see large deviations in nozzle flow rate across your boom, it could be an issue with your system plumbing. Similar to other application equipment, the length of solution hoses, hose routing, and the type of fittings used can restrict the flow of product to some sections. These problems can be harder to correct but are important to test for and understand if they exist on your machine.

If your machine is having trouble achieving your desired flow rate across the whole boom it could be an issue with your rate controller or flow meter. If you think your flow meter may be the culprit, you can remove it and have it recalibrated at your local dealer to ensure its accuracy. Before adjusting or troubleshooting these systems, make sure to consult your dealer or owner’s manual to properly understand the impact any changes you make could have. Entering in a wrong flow meter calibration or not configuring the rate controller properly could cause significant issues and inaccuracies with the rate control system.


Meaghan Anderson Field Agronomist in Central Iowa

Meaghan Anderson is a field agronomist in central Iowa and an extension field specialist at Iowa State University Extension and Outreach. Educational programming is available for farmers, agribusinesses, pesticide applicators, certified crop advisors, and other individuals interested in...