Determine GPA: Fill the tank with water and operate briefly to fill all parts with water. Refill the tank and spray for a measured distance at the selected pressure and speed of travel. Measure the number of gallons of water required to refill the tank. The application rate is the gallons required to refill the tank divided by the area covered.
In much of Ohio, the length of fields is known accurately from the method of surveying used. A section (640 acres) is 320 rods (1 mile) on a side. A quarter section is 160 rods (1/2 mile) on a side. Thus, typical field lengths are 160, 80, or 40 rods.
Example 6Nineteen gallons of water is required to fill the tank after traveling 40 rods (1 rod = 16.5 feet). The sprayer has 35 nozzles spaced 20 inches apart.
Acres sprayed = (width of spray pattern in feet x distance traveled in feet) /43,560 sq. ft./ac.
Width of spray pattern= (35 nozzles x 20 in./nozzle)/12 inches/foot = 58.33 ft.
Distance traveled = 40 rods x 16.5 feet/rod = 660 ft.
Acres sprayed= (58.33 ft. x 660 ft.)/ 43,560 sq. ft./ac.= 0.88 acres
GPA = 19 gal./0.88 acres = 21.5 gallons per acre
If in Example 6, you had been attempting to obtain an application rate of 20 GPA at 4 MPH, you would probably not be concerned that 1.5 gallons more liquid is being applied than planned for. The mixture of water and A.I. is formulated by using the actual quantity of liquid being applied per acre.
Formulating the mixture: After determining the gallons being applied per acre, find the number of acres to be covered with each tank of material. The number of acres covered with each tank equals the tank capacity in gallons divided by the gallons applied per acre.
Example 7Assume an application rate of 21.5 GPA (from Example 6) and a tank capacity of 200 gallons.
acres/tank = 200 gal/tank/21.5 GPA = 9.3 acres/tank
To find the amount of chemical to add to the tank multiply the acres covered with each tank by the amount of material to be applied to each acre.
Example 8The chemical manufacturer recommends that 4.75 pints of chemical be applied per acre. Assume that 9.3 acres will be covered with each tank of material (from Example 7).
Pints of chemical to add to 200 gallon tank = 4.75 pts/ac * 9.3 acres = 44.2 pints
There are 8 pints per gallon. Gallons to add to 200 gallon tank = 44.2 pts / 8 pts/gal = 5.5 gallons of chemical
Some recommendations will give the pounds of A.I. to be used per acre rather than the total amount of the chemical as in the preceding example. In such cases the amount of material to be applied may be calculated as in Example 9.
Example 9Two pounds of A.I are to be applied per acre. The material to be used is a wettable powder containing 50% A.I.
Pounds of material per acre = (2 Ibs. A.I./Ac) * (1 lb. mat'l/0.5 lb A.I.) = 4 Ibs. mat'l.
When using wettable powders, fill the spray tank one-third to one-half full of water. Mix the WP with water in a bucket to form a slurry. Start the agitator and pour the slurry into the tank. Fill the tank with water. Keep the agitator running until the tank is empty.
Check the acres covered per tank of material. If you find the application rate slightly high or low, either change the speed of travel slightly or adjust the pressure to obtain the correct application rate.