ENVIRONMENTAL EDUCATION SERIES
ENVIRONMENTAL QUALITY
Agriculture & Natural Resources
EXTENSION ENVIRONMENTAL EDUCATION, AUBURN UNIVERSITY, AL 36849-5647
Fertilizer Applicator Calibration
(Drop-Type)
ANR-725, 1992. By Charles Ogburn, Extension Agricultural Engineer (Retired),  Agriculture, Auburn University
The importance of accurate application of fertilizers is recognized by those in agriculture now more than ever. We can no longer afford to over-fertilize because of added cost of production, inefficient use of our energy resources, and the possible danger to our environment. Not applying enough fertilizer will also have negative effects. Proper calibration of fertilizer applicators can help assure accurate and evenly distributed amounts of fertilizer to our crops.

The pounds of material applied per acre for large volumes (10 pounds and up) can be determined by using the following procedure. This calibration procedure is based on 1/16 of an acre, which is equal to 16 ounces in a pound of material. The measured distances shown in Table 2 correspond to those found in liquid sprayer calibration procedures, but the material collected is multiplied by 8 to obtain rate per acre.

A weight scale incremented in ounces is needed for this procedure. Check uniformity of outlets across the swath or row. Collect from each outlet for a specific time and weigh the material. Each outlet should be within 5 percent of the average output. Extreme care should be exercised and protective equipment used when an active ingredient is involved.
 
Step 1. Determine the type of application to be made and select appropriate procedure from Table 1. Example: Broadcast - Procedure A

Table 1.

Type of
Fertilizer
Application		 Procedure Coverage Basis
(volume of
application)
Broadcast
Band		 A
B		 Broadcast (lbs./acre)
Broadcast
(Lbs./acre of band)
Note: Determine and use average row spacing for modified row patterns. Use width of area covered per row spacing in skip row patterns for broadcast rates.

 
Step 2. Using procedure A or B as selected in Step 1, determine appropriate calibration distance from Table 2.
(A) Broadcast Application: Outlets must be evenly spaced. Measure outlet spacing. Find this spacing in left column of Table 2, and read the corresponding calibration distance. Example: For a 19-inch spacing, the distance would be 215 feet.
(B) Band Application: Measure band width. Find this band width in the left column of Table 2, and read the corresponding calibration distance. Example: For a 12 inch band, the distance would be 340-feet.

Table 2.
 
Row Spacing or Outlet Spacing
or Band Width (whichever applies)		 Calibration
Distance
48 inches
46
44
42
40
38
36
34
32
30
24
20
19
18
12
10
8		 85 feet
89
93
97
102
108
113
120
128
136
170
204
215
227
340
408
511
To determine distance for spacing or band width not listed, divide the spacing or band width expressed in feet into 340.

Example: For a 13-inch band, the calibration distance would be 340 divided by 13/12 = 314 feet.
Note: To increase calibration accuracy for a wide outlet spacing, multiply calibration distance by a factor (for example, 2). Then, divide Step 7 by the same factor for pounds per acre. For narrow spacings with long calibration distances, divide calibration distance by a factor (for example, 4). Then, multiply Step 7 by the same factor for pounds per acre.
 
 
Step 3. Measure and mark calibration distance in a typical field application site.
Step 4. With all attachments in operation (harrow, planters, etc.) and traveling at the desired operating speed, determine the number of seconds it takes to travel the calibration distance. Be sure machinery is traveling at full operation speed the full length of the calibration distance. Mark or make note of engine RPM. Machine must be operating at same speed used for calibration.
Step 5. With applicator sitting still and operating at same speed as used in Step 4, adjust gate openings to desired setting.
Step 6a. For procedure (A), Step 2, broadcast application, collect from one outlet for the number of seconds required to travel the calibration distance. For procedure (B), Step 2, band application, collect from all outlets used on one band width for the number of seconds required to travel the calibration distance.
Step 7. Weigh the amount of materials collected in ounces. The number of ounces collected multiplied by 8 is the pounds per acre rate on the coverage basis, as indicated in Table 1. For example, if you collect 40 ounces using procedure (A) or (B), the applicator will apply 40 multiplied by 8 = 320 pounds per acre on a broadcast coverage basis. Adjust applicator speed, gate opening, etc.. to obtain recommended rate.
Step 8. Check applicator for proper calibration every four to eight hours of use. Simply repeat steps 6 and 7. If there is a difference of more than 5 percent of original calibration, check the system.
aFor ground-driven equipment, multiply the calibration distance by 8, and collect from each outlet while driving the calibration distance.

Band Application

To determine the pounds of material required to make a band application on a field, the number of acres that will be in the actually treated band must be determined. When all treated bands are the same width and all untreated bands are the same width, which is usually the case, the acres in the actually treated band can be calculated by placing the width of the treated band over the sum of the treated and untreated band, and multiplying this fraction by the number of acres in the field. Example: How many acres will actually be treated in a 30 acre field if a 12-inch band of material is applied over the drill of rows spaced 36 inches apart?  The treated band width is 12 inches. The untreated band width is 24 inches. Acres actually treated will be:
 

     12"    
12" + 24"		 x 30 acres = 10 acres

The amount of material required will be 10 times the number of pounds per acre from Step 7.

Carefully check rate recommendations as to type of application, broadcast, band, and type of material specified (formulated product, active ingredients, etc.).

For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.
Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability. 

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