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  • 1 Post By Halloamey

Fertilizer help with calculating ppm N

This is a discussion on Fertilizer help with calculating ppm N within the General Orchid Culture forums, part of the Orchid Culture category; I'm trying to learn the breakdown of different amounts of fertilizer and their ppm N. ...

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  1. #1
    nicki is offline Senior Member
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    Default Fertilizer help with calculating ppm N

    I'm trying to learn the breakdown of different amounts of fertilizer and their ppm N. I know most recommend the 'weakly weekly' or 1/4 strength of a 20-20-20 fertilizer. I'd like to know what makes a fertilizer weak or strong and be able to look at any type of fertilizer and know how much I should use for the amount of ppm N I want.
    I thought I had it figured out but everywhere I look the numbers are different. Between the book I have at home, an online article, fertilizer calculator and bottle labels I'm getting all kinds of different numbers. I'm not sure where the error is and I was never good with math.

  2. #2
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    Halloamey is offline Senior Member
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    I think I had written it earlier, but here we go again, the number 20:20:20 or 5:10:15 or 0:20:50 etc denote the percentage of the elements Nitrogen:Phosphorus:Potassium (NPK) by weight in a fertilizer,

    so 100g of 20-20-20 contains 20 g each of N,P,K to make a total of 60 g the remaining 40 g are contributed by other elements like Oxygen (O), Carbon (C), hydrogen (H), and may be Calcium (Ca), Magnesium (Mg) etc depending on the type of the fertilizer.
    Now 1 g= 1000 mg
    so 1 g 20-20-20 fertilizer contains 200 mg each of NPK

    Now,

    PPM (Parts Per Million) for calculation purposes is mg/litre or mg/Kg
    1 kg = 1000g = 1000,000 mg
    So if you add 1mg of Nitrogen to 1 litre of water you have a 1ppm solution (1 part of Nitrogen per 1 million parts of water)

    Nitrogen fertilization is recommended between 100-300 ppm for our calculation purpose let us consider 200 ppm.
    1 g of 20-20-20 fertilizer contains 200 mg Nitrogen, so when you add 1g of this fertilizer into 1litre (1000 g) of water, you have solution that has 200 ppm N, 200 ppm P and 200 ppm K.

    If you want 100 ppm Nitrogen you dissolve 0.5 g fertilizer in 1 litre of water and if you want 300 ppm you dissolve 1.5 g fertilizer in a litre of water.

    I hope this was helpful, feel free to ask if you have any more doubts.

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    nicki is offline Senior Member
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    Thank Amey. I had to read it a couple times but I think I got it

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