Suzana, one of the first members of My Grape Vine, send me this question a few days ago.

She wanted to know what those numbers on a fertilizer packaging means.

With this article, I will show exactly what they mean and how you can calculate, precisely how much of a certain fertilizer mixture you must apply, in order to get the right amount of an element in your soil.

The numbers on a fertilizer mix like for example a 10:10:10 fertilizer, probably the most common of all, means:

10 : 10: 10

N  :  P :  K

10 parts nitrogen (N), 10 parts phosphorus (P), 10 parts potassium (K)

 

But that’s not all!  On many fertilizer packages you see a 4th number in brackets; for example

2:3:4 (27)

 

From what we have just learned, we will have

 

2 parts nitrogen (N),  3 parts phosphorus (P),4 parts potassium (K)

 

The fourth number (27) – in brackets – is the total percentage (%) of nutrients in the mixture.  

So we have a total of 9 parts ( 2 + 3 + 4) nutrients in that mixture, that ads up to 27% of the total mixture.

 

In other words; for every 100 kg of fertiliser there will be a total 27 kg N, P, K in the mixture.

                                            2          27

the nitrogen (N) is                  9   x     1      =   6     kg N for every 100 kg of fertilizer mixture

 

Therefore, two ninths of 27 kg, or 6 kg, of every 100 kg of mixture will be nitrogen.

 

As for a 1:0:0(40) mixture, 40 kg Nitrogen will be added to the soil for 100kg fertilizer and no P, K

 

I hope this makes sense? 🙂

With this formula, you can easily calculate how much of a certain fertilizer mix you must apply to add a certain amount of N:P:K to the soil.

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