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 for any given soil do not exactly match a fertilizer, select a fertilizer that gives comparative amounts of nitrogen, phosphorus and potassium as recommended by the soil test. In fertilizer application, it is most important to match the nitrogen requirement and compromise some for the phosphorus and potassium. The amount of fertilizer to apply that will give the recommended amount of nitrogen can be obtained from the following table:


Table 1. Amount of fertilizer to apply based on actual nitrogen recommendations
Nitrogen Rage:
0.1 pound N
per 100
square feet
0.2 pound N
per 100
square feet
1 pound N
per 1,000
square feet
Fertilizer Grade pounds fertilizer to apply per 100
square feet
pounds fertilizer to apply per 100
square feet
pounds fertilizer to apply per 1000
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
0.6
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
1.0
2.0
10.0
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 N (nitrogen) recommendation is for 0.1 lb. N/100 sq. ft. and the fertilizer grade selected has a ratio of 18-6-12 (column 1), apply 0.6 lb. of this fertilizer per 100 sq. ft.



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Authors: David Whiting (CSU Extension, retired), Adrian Card (CSU Extension) and Carl Wilson (CSU Extension, retired) Reviewed by Eric Hammond (CSU Extension)

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Revised October 2014, Reviewed 2015

Updated Wednesday, January 13, 2016 by Mary Small

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