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Fertilizer Conversion Charts for Various Organic Soil Additives

For all of you who are struggling to make sense of your soil test results, here is a very handy chart to put into your garden journal or reference library to help you figure out how many pounds of coffee grounds you might possibly need to give enough nutrients to your vege gardens.

As a rule you can plan on having to add some source of N to your soil on a yearly basis for optimum growth. But, how much??? Too little and the plant is stressed and too much you get problems with aphids and reduced flower/fruit set. Well there is very wide margin for error and you can print the attached pdf – Soil Additive Nutrient Content and Fertilizer Equivalency Charts

Virginia Tech says: “Vegetables recommended application rate: Apply one pound of 10-10-10 or two pounds of 5-10-5 (or 5-10-10) per 100 feet of row”.
Remember, 10-10-10 means that there is 10% actual N, 10% actual P, and 10% actual K per 1 lb of fertilizer in that bag.

So if your soil test says you need to apply “2 lbs of 5-10-10 per 100 ft row” which is equal to 1 lb per 50’ row…..1/5 lb per 10 ft row etc. you are good to go.

But let’s say, you have the fertilizer and you want to know how much to apply to your asparagus crop say.

  1. Find out the recommendation for your crop. Asparagus is a bit less than 2 oz N per 100 sq ft.
  2. Next, determine the amount of fertilizer needed to apply the recommended amount of nutrient. Divide the ounces of N recommended (2) by the percentage of N (.05) in the fertilizer: x oz 5-10-10/100 sq ft = 2/.05 (always keep your units straight!) x = 40/100 sq ft.
  3. Total 5-10-10 fertilizer needed to supply 2 oz N per 100 sq ft = 40 ounces (16oz = 1 lb) = 2 ¼ lb/100 sq ft.

Tips to avoid confusion: always write your units into your equations so you don’t forget what they are.

Examples –

  • Ammonium Sulfate with 21% N: If four ounces of N is required, divide 4 by .21 (% of N in the product). Thus 19 ounces (1 pound plus three ounces) of ammonium sulfate are needed to supply the 4 ounces of N needed. Note: One cup of ammonium sulfate weighs approximately 8 ounces.
  • Corn gluten with 9% N: When four ounces of N is needed then slightly over 2 ¾ pounds of corn gluten needs to be applied (4 ÷ 0.09 = 44.4 ounces (2.78 pounds). Note: One pound=16 ounces.


Kirsten Conrad Buhls, Extension Agent

Agriculture Natural Resources – Horticulture
Fairlington Community Center 3308 S. Stafford St. Arlington, VA 22206
Phone: 703 228 6423 Email: kbuhls@vt.edu Fax: 703 228 6407
Serving Arlington County and the City of Alexandria

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