Calculating Fertilizer Rates

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Steps to Calculating Fertilizer Application Rate

Example is for a 40 foot by 100 foot lawn area, using a 20-2-2- fertilizer.


calculating fertilizer rates

Fertilizer Application Rate Table

Because soil test recommendations may not exactly match any fertilizer select a fertilizer that gives comparative amounts of nitrogen, phosphate and potash. In fertilizer application, it is most important to match the nitrogen requirement. The amount of fertilizer to apply that will give the recommended amount of nitrogen can be obtained from Table 1.


Table 1.
Amount of fertilizer to apply based on actual nitrogen recommendations
Fertilizer Grade
0.1 pound N per 100 square feet
0.2 pound N per 100 square feet
1 pound N per 1,000 square feet
45-0-0 (urea)
0.2
0.4
2.2
37-3-3
0.3
0.5
2.7
36-6-6
0.3
0.6
2.8
33-0-0
0.3
0.3
3.0
32-4-4. 32-3-10
0.3
0.6
3.1
30-4-4, 30-0-10
0.3
0.7
3.3
28-3-3, 28-4-6
0.4
0.7
3.6
27-7-7, 27-3-3
0.4
0.7
3.7
25-5-5, 25-3-12
0.4
0.8
4.0
24-8-16, 24-0-15
0.4
0.8
4.2
22-4-4, 22-6-3
0.5
0.9
4.5
21-0-0, 21-3-12
0.5
1.0
4.8
20-20-20, 20-4-8
0.5
1.0
5.0
19-19-19,19-11-12
0.5
1.0
5.3
18-6-12, 18-3-6
0.6
1.1
5.6
16-8-8, 16-4-8
0.6
1.3
6.3
15-15-15, 15-5-5
0.7
1.3
6.7
13-3-9, 13-25-12
0.8
1.5
7.7
12-12-12, 12-4-4
0.8
1.7
8.3
10-10-10, 10-20-10,
10-5-5, 10-10-20
1.0
2.0
10.0
6-12-12, 6-2-0
1.7
3.3
16.7
5-10-10, 5-10-5
2.0
4.0
20.0
Example: If the nitrogen recommendation is for 0.1 pound Nitrogen per 100 square feet, and the fertilizer grade selected has a ratio of 18-6-12 (column 1), apply 0.6 lbs. of this fertilizer per 100 sq. ft.
Note: Two cups (one pint) of dry fertilizer weight about 1 pound.



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Authors: David Whiting (CSU Extension) with Carl Wilson (CSU Extension, retired). Artwork by David Whiting.

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  • Copyright. 2011. Colorado Master Gardener Program, Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced without change or additions, for nonprofit educational use.

Revised December 2011

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