Calculating Fertilizer Rates

Outline

• Steps to calculating fertilizer application rate
• Fertilizer application rate table

Steps to Calculating Fertilizer Application Rate

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

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.

Additional Information

CMG GardensNotes on fertilizers

• Calculating Fertilizer Application Rates, #233
• Iron Chlorosis, #223
• Organic Fertilizers, #234
• Plant Nutrition, #231
• Soil Tests, #221
• Understanding Fertilizers, #232

CMG GardenNotes on soil amendments

• Cover Crops and Green Manure Crops, #244
• Making Compost, #246
• Soil Amendments, #241
• Using Compost in the Home Garden, #243
• Using Manure in the Home Garden, #242

CMG GardenNotes on soil management

• Asking Effective Questions about Soils, #251
• Earthworms, #218
• Estimating Soil Texture, #214
• Introduction to Soils, #211
• Iron Chlorosis, #223
• Managing Soil Tilth, #213
• Mulches for the Vegetable Garden, #715
• Mulching with Wood/Bark Chips, Grass Clippings and Rock, #245
• Soil Compaction, #215
• Soil Drainage, #219
• Soil pH, #222
• Soil Tests, #221
• The Living Soil, #212


• References and Review Questions: Soils, Fertilizers and Soil Amendments, #210
• Homework: Soil, Fertilizers, and Soil Amendments, #253
• Worksheet: Soil Texture and Structure Lab, #252

Authors: David Whiting with Adrian Card and Carl Wilson (CSU Extension)

• CMG GardenNotes are available online at www.cmg.colostate.edu
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• No endorsements of products mentioned is intended nor is criticism implies of products not mentioned.
• Copyright. 2010. 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