1. Calibration: What does it tell us?
How much herbicide to put in the sprayer
How much herbicide to purchase
How many acres will be sprayed per tank.
How much water/herbicide mixture is being applied / acre.
How fast to drive the tractor/vehicle

2. Spraying with a backpack sprayer

3. Whether spot treating or blanket spraying, we need to know how much water per acre our sprayer is putting on the ground.
To find this, we use the 1/128th method.
We will need to know a few constants to use this method. So first we’ll derive where those constants come from.

4. An acre is 43,560 sq. ft.
1/128 of an acre is sq. ft.
We take the square root of to find Height and Width of our area
This gives us a weird number (18.44) so for easy math, we’ll call it 18.5 ft².
So, now we know that 1/128th of a square acre is 18.5 ft. X 18.5 ft.

5. Now, we also need to know that there are 128 ounces in a gallon
Now, we also need to know that there are 128 ounces in a gallon. Seeing any trend yet?
We will measure an area 18.5 X 18.5 (1/128 of an acre)
We will spray that measured area with our backpack until the ground is wet, but not forming puddles.
We will time how long it takes to spray that measured area.
We will then spray our backpack into a bucket for the same length of time it took to spray our measured area.
Now, we measure the amount of water captured in the bucket, in ounces. Why ounces? Because if we are going to convert both 1/128th of our gallons and 1/128th of our acres, back to Gallons and Acres, we need to measure in ounces, and spray 18.5 ft². Make sense?

6. The ounces you sprayed into the bucket are going to equal the gallons your sprayer applies per acre.
No, it’s not magic
It works because 1 ounce sprayed on 1/128 of an acre….is the same ratio as 1 gal sprayed on a full acre.
Remember……

7. 128 oz. /gal of water and there are 128 squares (18. 5 sq. ft
128 oz./gal of water and there are 128 squares (18.5 sq. ft.) in an acre
So, 1/128 of a gal. is 1 oz.
And, 1/128 of an acre is 18.5 X 18.5 ft.
So, 1/128 of a gallon sprayed on 1/128 of an acre would show you ounces applied per 18.5 ft x 18.5 ft. area.
If we scale both the .oz’s and the area, up by 128 to eliminate the fraction, we end up with gallons and acres, instead of oz’s and 18.5 ft².
Because we are dealing with the same fraction of water as we are the fraction of an acre (1/128) We know that the ounces collected within that 18.5ft² area is the same number as the gallons collected per acre, going the same speed, using the same nozzles, at the same pressures.

8. Gallons and Acres 128 ounces in a gallon
1/128th/gal = 1 oz.
1/128th/Gallon
128 plots of 18.5 ft² plots/acre
1/128th/acre = 18.5 ft²
1/128th/Acre
One ounce
(1) 18.5 x 18.5 ft area
Get rid of the fraction, by scaling
Both side up 128 times, you end up with
1/128
1/128
Gallons and Acres

9. Example: Bob measured out an area 18.5 ft X 18.5 ft.
He had a stop watch and started timing as soon as he began to spray the area.
It took him 30 seconds to spray the 18.5 ft. x 18.5 ft. area.
He then sprayed his backpack into a bucket for the 30 seconds.
He then measured the water in the bucket with a measuring cup, in ounces.

10. He found that when he sprayed for 30 seconds into the bucket, he collected 24 ounces of water.
Since he knew that the ounces he collected were going to equal the gallons per acre..
He knew he was spraying 24 gallons of water for every acre he sprayed.
So the calibration, no matter what herbicide, is gal/acre. As long as the pressure, speed, and nozzle size remain the same. This is the calibration for Bob’s backpack.

11. Now that Bob knows his backpack sprays 24 gallons of water per acre, he realizes another problem…….
His backpack only holds 4 gallons!!!

12. Not accepting defeat, he remembered that his total water (mixture) sprayed/acre was 24 gal.
And, he knew his backpack was a fraction of that total.
Since the backpack is only 4 gal. He knows it would take 6 of those backpacks to spray 24 gallons. (6 packs/acre X 4 gal/pack = 24 gal/acre)
By knowing this, he can determine how much herbicide to put in each backpack.

13. Since each backpack covers 1/6th of an acre (6 packs treat an acre) he knows that any herbicide with a “per acre” rate, needs be divided up among 6 backpacks evenly.
He wanted to spray Round-Up® and the label said to use 2 qts/acre
Knowing that there are 4 qts/gal and 128 oz./gal, he knew that by dividing 128 by 4 he would know how many ounces were in a quart.
He found there are 32 oz./qt and the label called for 2 qts/acre so that would be 64 oz./acre

14. Bob already knew it takes 6 backpacks to spray an acre, so he figured out it takes 6 backpacks to apply 64 oz. of Round-Up® per acre
By dividing 64 oz. evenly among 6 backpacks, he knows he has to add 10.5 oz. of Round-Up® every time he fills his 4 gallon backpack up.
For every 6 backpacks he sprays, he has sprayed 1 acre of vegetation and used 2 qts. (64 oz.) of Round-Up®
If he walks over 50 acres of land, and sprays 6 backpacks, then he treated 1 acre of weeds within that 50 acre area that he walked.

15. ARE YOU STILL PAYING ATTENTION?

16. Moving On Then!!
Whew!! Lets move on to something a little easier to explain.
There are two main types of field-type sprayers
Boomless sprayers: These are sprayers that broadcast spray without the use of spray bars (booms)
Boom Sprayers use multiple nozzles fixed to a spray bar to spray a certain width.

17. A typical boomless sprayer would have one or two jets mounted to an ATV, truck, or tractor

18. Going The Distance…. Since we know that an acre is 43,560 sq. ft.
We need to change that area into a linear distance. This will tell us how far we need to spray in a straight line to cover an acre of ground.
To find this distance, we first need to measure how wide our spray swath is…..

19. By leaving the spray vehicle stationary, we can turn the boomless jets on and measure the wet line it creates on the ground.
We then take 43,560 ft. (an acre) and divide it by the measurement you took of the spray strip on the ground.
This gives us the linear distance needed, to cover an acre of land.

20. Example:
After turning the ATV sprayer on for a few seconds, we measured a 26 foot wide spray mark on the ground.
So, 43,560 ft. / 26 ft. = 1675 ft.
Our square acre just turned into a rectangle that is 26 feet wide and 1675 feet in length. Same area inside, just different shape.
Obviously this is too long to measure with a tape….so we can just take 1/10th of 1675….as long as we remember to multiply back by 10 when we get our answer.
This makes the distance to travel ft.

21. The Speed
Now that we know how far to travel, we need to pick a speed that is going to allow us to get good spray coverage, and safely operate the sprayer on our terrain
Typically this is anywhere from 3 to 5 mph. Once you pick a speed, stay with that speed….or your calibration will change.
Now we need to park our sprayer on level ground and fill the tank up to the brim (or another mark on the tank we can use for refilling) with water.
Once full, we go to our start line……

22. As we pass the start line, we want to make sure we are traveling the desired speed (lets use 4 mph)
We turn the boomless jets on as we pass the start line.
Maintaining our speed at 4mph throughout the measured distance, we remember to turn off the sprayer at the end of our measured distance.
Upon returning to our level “fill up” spot, we can calculate how much water we just sprayed out.
We fill a measuring cup with water and pour it into our spray tank. We repeat this step until the tank is full to the brim (or a mark on the tank).
Remember to keep track of the ounces you pour into the tank.

23. Now, we just need to convert those ounces to gallons…
Since we measured in ounces, we’ll first multiply the amount we poured back into our tank by 10. Right??? (to get back to an actual acres, since we only measured 1/10th of the actual distance of an acre)
Once we have the actual number oz’s, we simply divide that number by 128 (the number of oz’s in a gallon). This new number is the gallons per acre you would have sprayed, had you traveled the entire distance of an acre, at 4 mph.

24. EXAMPLE:
Bob just bought a new ATV and a spray tank with boomless jets.
He wants to calibrate his spray rig, using the “refill method”.
What is the first thing he should probably do?

25. A. After filling the sprayer, turn it on and measure the swath width on the ground. (The wet line on the ground)
B. Find a level spot and fill it to the brim (or a mark on the tank)
C. Measure an acre and go spray it
D. Just fill the tank up and get to work

26. B. Find a level spot and fill it to the brim (or a mark on the tank)
ANSWER:
A. After filling the sprayer, turn it on and measure the swath width on the ground. (The wet line on the ground) OR
B. Find a level spot and fill it to the brim (or a mark on the tank)
Since we don’t like standing in the mud to refill our sprayer, I would suggest answer A.

27. O.k…so we know our swath width…now what???

28. 43,560 / swath width = Distance needed to travel 1 acre.
The number will be too big to measure on the ground, so we’ll take 1/10th of the distance.
We’ll measure the distance on the ground, marking the beginning and end points.
Now are we ready to fill the ATV ??
Remember this part…

29. YES!, As soon as we find a level spot.
We will fill it up to the “brim” (or an easy to read “refill mark” on the tank)
We will spray along our measured distance traveling 4 mph (or a speed you plan to use)
Now, we’ll go back to our level spot and refill our tank…USING A MEASURNG CUP SO WE KNOW HOW MUCH WAS SPRAYED OUT!!!

30. Hmmmm.
SO….now we have the amount of water in ounces, needed to refill our tank.
Is that all we need to know??

31. No, we need to convert those ounces into gallons.
Divide the number of ounces you poured back into the tank by 128 (because there are 128 oz/gal)
^^This^^gives us our water in gallons……but wait!!
We only used 1/10th of the total distance needed to travel an acre REMEMBER??
So, we need to multiply our gallons by 10…that will tell us how many gallons we spray per acre.

32. Example After Bob measured his swath he found it was 24 ft. wide
By dividing 43,560/24 he knows 1,815 ft. is how far he has to travel to spray an acre.
That’s too far to measure, so he used 1/10th of that number….181.5
He then measured a line on the ground ft. long, and marked a start and end point.

33. After filling his tank on a level spot, Bob made sure he reached 4 mph as he was passing his start point.
He then turned on his sprayer, and maintained his 4 mph speed the full length of the line measured.
After reaching the end of his line, he shut the sprayer off and returned to his level re-fill spot. He found that he had to add 307 oz of water to his tank. He wanted gallons, so he divided 307 by 128 and arrived at 2.4 gal of water to fill his tank back to the original mark.
He remembered that he only used 1/10 of the total distance, so he multiplied that 2.4 gallons by 10 to arrive at a total of 24 gallons per acre
He now has to figure out how much water his tank holds….he finds that it holds 12 gallons

34. How Much Chemical Do We Add???
Since the tank holds 12 gallons and the sprayer is applying 24 gal/acre, we can see that the tank will spray ½ an acre at a time (12/24=1/2 acre)
By reading the label, We will see that the “rate per acre” for any herbicide is listed in quarts, ounces, etc..
To calculate how much to add to each tank, we need to know how many ounces are in a quart.
We know there are 128 oz. in gallon, and there are 4 qts. In a gallon
Therefore, we know the 128/4 = 32 oz./quart

35. So, the herbicide label says 2 qts
So, the herbicide label says 2 qts./acre of the herbicide to control Bob’s target weed…
We know from our calibration that our sprayer applies 24 gal/acre, when traveling 4 mph.
So…. Since we know our tank is only 12 gallons, which is only 1/2 the water needed to treat an acre, we would only add 1 qt (32 oz.) per tank.
After spraying two tanks (24 gal), we would have sprayed one acre of weeds and used 2 qts. of herbicide…. As long as we maintained the 4 mph speed while spraying.

36. REMEMBER…. 1/128 of a Gallon = 1 Ounce
1/128 of an Acre = 18.5 ft. X 18.5 ft.
43,560 sq. ft in an Acre
4 qts in a gallon, 32 oz in a quart

37. Any Questions???

38. Great!! Lets look at calibrating an actual multiple nozzle “Boom Sprayer”
We are going to use the 1/128th method again… How you ask??
We know the 1/128th of an acre is 18.5 ft x 18.5 ft, or 340 sq ft…
What would happen, if we turned that 18.5 x 18.5 square area, into a rectangle that was say…..about the width between the nozzles on your spray boom?
Wouldn’t it still equal 340 sq. ft. inside?? YES, the answer is yes, now wipe the drool off your shirt, we’ve got work to do..

39. Using what we’ve already learned about the 1/28th Method, we know that the ounces sprayed in our measured area (which is 1/128th of an acre, but now just a very narrow rectangle..) will be equal to the gallons we spray per acre Once we’ve accepted the facts, that we simply changed the shape of our 1/128th of an acre, and there is (and always will be) 128 oz’s in a gallon, so an ounce is 1/128 of a gal Using what we’ve already learned about the 1/28th Method, we know that the ounces sprayed inside our measured area (which is 1/128th of an acre, but now just a very narrow rectangle..) will be equal to the gallons we spray per acre Once we’ve accepted the facts, that we simply changed the shape of our 1/128th of an acre, but not the area… and there are (and always will be) 128 oz’s in a gallon, so an ounce is 1/128 of a gal.. We can begin to wrap our minds around why we only need to use a single nozzle on the boom bar, no matter how many nozzles are present. Wait……What????

40. So here’s the deal:
All we did was change the shape of our area to a shape as wide as the spray pattern on ONE nozzle.
We basically turned our multiple nozzle sprayer, into a single nozzle calibration
Why? Because our sprayed area isn’t calculated based on the entire width of the boom bar. If it were, we would have to collect the oz’s from ALL of the nozzles at once….Which is above my pay-grade.
So, we made a long slender rectangle, that takes longer to travel, instead of a short fat one, that would be the width of the entire boom. Both rectangles would be the same area inside (1/128th of an acre) Makes our job pretty easy right? Catching water out of one nozzle, instead of dozens…

41. So here we are…
Ready to spray some water out of a nozzle, for a given amount of time, and call the ounces collected the same as the gallons per acre
Before we head down this path to success, we better make sure our pressure is where we like it, and not creating a lot of mist.
We also need to make sure all of the nozzles are the same, and are putting the same amount of water on the ground. To do this, we fire up the tractor and hold the measuring cup under each nozzle for ten seconds. If life is good, each nozzle should spray the same amount of water into the cup, when timed for the ten second interval. If this is not the case, we need to clean screens, replace nozzles, fix leaks, etc…
O.k., now we need to measure the distance between each nozzle. That has to be the same, or darn close to it… Why? Because we can’t measure a rectangle as wide as the spray pattern on one nozzle, if it’s different than all of the others.

42. Now that are nozzles are evenly spaced, our pressure is where we like it, and the nozzles are all spraying consistent amounts of water during the 10 seconds we captured water out of each one, We Are Ready To Calibrate!
We know the distance between our nozzles is going to equal the spray pattern of an individual nozzle, unless you like stripes of untreated weeds across your golf course..
So we take the distance between two of the nozzles, and call that the width of our rectangle that is 1/128th of an acre, or 340 sq. ft. Since we know the width, and the area, we just need to divide the area by the width to get the length…Right? Yes, except our width is in inches, and our area is in feet. So, let’s keep everything in inches. (340 ft x 12 inches = 4084)
4084 inches are inside of 1/128th of an acre (no matter what shape it is) So, 4084 divided by the width between two nozzles = equals the distance we need to travel (while spraying)
If we were to pick a speed, travel that distance, time ourselves, then collect water out one nozzle for the amount of time, our ounces will equal the gallons per acre..
Luckily, because of the fine work they do at U.W. we don’t even have to move the tractor..

43. This chart shows us how far we have to travel (Distance in ft), based on the nozzle spacing (W). Once we choose a speed, it also tells us how long it would take to travel that distance (1/128th of acre).

44. So, all we have to do is measure the spacing between nozzles, select a speed, and hold a measuring cup under one nozzle for as many seconds as the chart tells us.
The ounces collected equal the gallons /acre !!

45. The rest is easy
How big is the tank?
Will it do many acres, or less than an acre?
Once we know this, we can multiply, or divide, the “per acre” rate on the herbicide label between tanks.
Lets do an example verbally.

46. ANY QUESTIONS??