I had a nifty android app that calculated carrier volume and tractor speed for spraying, but it stopped working after a recent upgrade. So, I did some web research and came up with a simple spreadsheet that I thought others might find useful. Here it is:
The formulas are displayed in the cell to the right of the calculation. It isn't as sophisticated as other spreadsheets that I have seen, but it is easy to use and has given me good guidance. After all, spraying is an approximation.
Here is how it works:
- nozzle size: output in gallons/minute of your nozzles at the pressure that you intend to use. I didn't calibrate my nozzles. I just used the nominal value published by TeeJet and spray at their recommended pressure (40 psi.) Slight alterations in pressure have negligible impact on the output of the nozzle.
- nozzle spacing - the distance between nozzles on your boom. (Interestingly, the formula doesn't use the boom width. That perplexed me for a while until I realized that the overall duration of the spray job is not part of the formula; only the speed of the rig. The speed is the same regardless of how many nozzles you have, but the more nozzles, the faster the job gets done.)
- The Speed Calc lets you specify the gallons/acre that you want to apply and calculates the speed that will achieve it.
- The GPA Calc lets you specify the speed that you want to travel, and calculates the gallons per acre that the specified speed will apply.
- I usually want to distribute about 2 qts of material/acre, in a volume between 20 and 30 gallons/acre, at a speed between 2-3 mph. So, I decide how much product/acre I want to apply, then play around with the two calculations until I find a speed and volume that I like.
- For example, if I want to distribute 20 gallons/acre, then I need to maintain a speed of about 3 mph.
- If I slow it down to 2.5 mph, then I will distribute about 24 gal/acre.
Disclaimer:These two calculations work very well for me. I found them on a few .com and .edu sites. Double check against examples in your sprayer manual, past records, other spreadsheets, etc and proceed with caution until you are comfortable with them. I suggest taking a few checkpoints along the way to confirm that the actual application rate matches what you calculated so that you can make any interim adjustments