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Fertilizer Calculations

How to use your report to select fertilizer products

The numbers provided in the “soil fertility guidelines” section of your Soil Test Report should be converted to pounds per 1000 square feet (lbs/1000 sqft):

  • For lime (expressed in tons per acre) multiply by 2000 and then divide by 43.56

  • For nutrients (expressed in pounds per acre) simply divide by 43.56

  • Please note that the "Soil Fertility Guidelines" are ANNUAL application totals

Example for Lime:

1. The following Soil Test Report indicates the need for limestone at a rate of 0.2 tons/ac.

2. Multiply by 2000 then divide by 43.56 to convert to 9.2 lbs/1000 sqft. This is your annual total for lime

2000 × 0.2 = 400

400 ÷ 43.56 = 9.2

All commercially available fertilizer products are required to include a “guaranteed minimum analysis” label somewhere on the bag. On this label you will find what percentage of the total bag weight is made up by each nutrient. Use these percentages to determine the most accurate product match.

Example for nutrients (N, P2O5, K2O, Mg, etc.):

1. The report below indicates a need for phosphorus (P2O5) at a rate of 100 lbs/ac.

2. Divide by 43.56 to convert to 2.3 lbs/1000 sqft. This is your annual total for phosphorus.

100 ÷ 43.56 = 2.3

3. If a 50 lb bag of fertilizer is made up of 20% phosphorus (let's call it a 0-20-0*), you will multiply 50 by 0.20 to find the total amount of phosphorus in the bag. In this example, the bag would contain 10 lbs of phosphorus.

50 × 0.20 = 10

*A product with 0% nitrogen, 20% phosphorus, and 0% potassium would be labeled as 0-20-0 (N-P-K)

4. Multiply the size of the bag (50 lbs) by the required amount of phosphorus (2.3 lbs/1000 sqft) and divide by the amount of phosphorus in the total bag (10 lbs). Based on this calculation, a 0-20-0 fertilizer would need to be applied at a rate of 11.5 lbs/1000 sqft.

50 × 2.3 = 115

115 ÷ 10 = 11.5

*If the product was made up of 100% phosphorus, your product application rate would have been 2.3lbs (note: such a product does not exist)

5. If your area size is 4800 sqft, you would divide by 1000 to get 4.8 then multiply by the application rate to determine the total amount of product to purchase for the year. In this case, you would purchase 2 bags and have product leftover for next season.

4.8 × 11.5 = 55.2

It is important to note that getting enough of one nutrient may mean that you will go overboard on another. You will need to be strategic in your choice of product(s) in order to find the closest match. Too much of a good thing can be just as detrimental as too little.

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