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When people ask me what I do for a living I tell them I am a dairy farmer. I think this is a fitting job description because in addition to caring for dairy cows, we also grow a lot of their feed.
We do all of our own field work, which includes spraying corn, wheat, & alfalfa. I am the farm manger and responsible for ensuring the spray equipment is operating properly and is calibrated. I use my smartphone to calibrate the spray rig.
First I enter the prescription from my PCA into an excel spreadsheet that tells us how much water and chemicals to include in the tank. In this example we will spray Roundup at 32 oz/acre in 15 gallons of water.
Before calibrating the sprayer, I need to determine the gallons per minute flow rate of each nozzle at the target rate. For this I use the SpraySelect app by TeeJet. I input the target speed (6.5 mph), nozzle spacing (20"), and gallons per acre (15). On the next page I select my spray tip. The app returns the calibration data, which is .33 GPM per nozzle at 48 PSI.
After checking for leaks and that everything is working correctly we adjust the spray pressure to 48 PSI. Next I find my measuring cup and pull out my phone. Using the built-in calculator app I convert gallons to ounces because the cup measures in ounces.
I enter .33 (Gallons) into the calculator and use Unit Conversion feature to get 42.24 ounces. I usually divide this number by 4 to get 10.56 OZ/15 seconds. This way I can get a rough idea of the calibration in a short time. Once you have checked several nozzles at 15 seconds do at least one nozzle for one minute to ensure your rate is accurate.
Next I switch to the Clock app and use the Stopwatch feature to time the collection of water for 15 seconds. If after 15 seconds the cup contains 10.56 OZ of water, we are calibrated and ready to go.
But before I go I switch my phone over to the Bubble Level app to ensure the three-point boom is level front to back. Once that is done, we are ready to fill tank and go spray.
At this point, the driver uses the iPad to check the spreadsheet we created earlier with the Dropbox app and adds the appropriate amount of water and chemicals to the tank.
Like many farmers, I have a variable rate sprayer that tells me the flow rate from inside the cab. But I have learned through experience that it is easier to spot nozzle wear using this method. Calibrating to a known speed and pressure gives you a place to fall back to if your variable rate equipment fails (which it often does).
You can use the same apps to calibrate for liquid fertilizer applications by including the specific gravity of the fertilizer.
For example, if you are applying UN32, set the specific gravity of the liquid to 1.32. You can easily figure out the specific gravity of fertilizer by dividing the weight of the fertilizer by the weight of water. In the example of UN32, it weighs 11.06 lbs/gallon and water weighs 8.6 lbs/gallon, so the math is 11.06/8.34 = 1.32.
Entering the proper specific gravity of your liquid fertilizer will help ensure accurate flow rates. Always remember to track your acres applied and gallons used to true up the calibration with real numbers.