The Numbers On Fertilizer Bags

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Each fertilizer bag has three or more numbers written in it to indicate the amount of each nutrient it contains.

The first number indicates the NITROGEN content measured as % N.

The second number indicates the PHOSPHORUS content measured as % P2O5

The third number indicates the POTASSIUM content measured as % K2O

Any additional numbers indicates the levels of other nutrients. These must be specified. This method of expressing nutrient content is internationally accepted and is law in many areas.

These numbers (the fertilizer formula) help in choosing the correct fertilizers.

For example, if the soil is deficient in phosphorus, then the second number must be high. In this case, 12.24.12 is suitable, 26.0.26 is not.

The formula also allows you to compare fertilizers. One bag of urea (46.0.0) provides more than twice as much nitrogen as a bag of ammonium sulfate (21.0.0).