Selecting Fertilizers Based on Soil Test Results

Nutrient Analysis on Fertilizer Labels

Fertilizer labels display three numbers to show the percentage by weight of nitrogen (N), phosphate (which contains phosphorus, P) and potash (which contains potassium, K), always in that order (N-P-K).

To Select a Fertilizer Product That Provides Nutrients Recommended in Soil Test Results

(1) Look at the pounds of N-P-K recommended in the soil test results. For example, the results might recommend 15 lbs N + 5 lbs P + 10 lbs K. The amounts recommended are usually for 1000 square feet of area.

(2) Find a fertilizer with the same ratio of those numbers. For example, 15-5-10 is the same ratio as 3-1-2 or 12-4-8 or 9-3-6. Do the best you can.

(3) If the test results recommend adding N, base the amount needed on N:

1- In the left column, find the percent of N in the fertilizer product.

2- In the top row, find the pounds of N recommended in the test results.

3- Find the intersection in the table, to find pounds of fertilizer to apply.

NOTE: If N is not recommended to be added, then base step (3) on any nutrient that the test results do recommend adding.

NOTE: Add amounts as needed. For example, if the soil test recommends 8 lb N, find the amount of fertilizer that provides 4 lb N, and multiply by 2.

Pounds of Fertilizer Product Needed to Supply a Specific Number of Pounds of a Particular Nutrient to a Specific Area

% of Nutrient in Product	Pounds of Nutrient Desired
% of Nutrient in Product	.5	1	1.5	2	2.5	3	4	5
0.2	250	500	750	1000	1250	1500	2000	2500
0.25	200	400	700	800	1000	1200	1600	2000
0.4	125	250	375	500	625	750	1000	1250
0.5	100	200	300	400	500	600	800	1000
1.0	50	100	150	200	250	300	400	500
1.5	33	66	100	133	166	200	250	330
2.0	25	50	75	100	125	150	200	250
2.5	20	40	60	80	100	120	160	200
3.0	17	33	50	66	83	100	133	165
4.0	12.5	25	37.5	50	73	75	100	125
5.0	10	20	30	40	50	60	80	100
6.0	8.3	16.5	25	33	40	50	66	83
7.0	7	14	20	28	35	40	55	70
10.0	5	10	15	20	25	30	40	50
12.0	4	8.3	12.5	16.5	20	25	33	42
15.0	3.3	6.6	10	13.3	17	20	25	33
20.0	2.5	5	7.5	10	12.5	15	20	25

From the GardenPro Answer Book; revised and updated by Lois Berg Stack, Ornamental Horticulture Specialist, University of Maine Cooperative Extension.