How to understand the label of NPK fertilizers
May 17, 2016

NPK fertilizers are three-component fertilizers provided by nitrogen, phosphor, and potassium.

NPK rating is a rating system describing the amount of nitrogen, phosphorus, and potassium percent by weight of a NPK fertilizer. NPK ratings consist of three numbers separated by dashes (such as 15-15-15 or 8-10-30) describing the chemical content of fertilizers.

The first number ‘N’ represents the percent by weight of nitrogen in the product; the second number ‘P’, P2O5; the third ‘K’, K2O. For example: a 50kgs bag of fertilizer labeled 6-12-36 contains 3kgs of nitrogen (6% of the 50kgs) an amount of phosphorus and potassium equivalent to that in 6kgs of P2O5 (12% of 50kgs) and 18kgs of K2O (36% of 50kgs). Most NPK fertilizers are labeled according to this N-P-K convention, few following an N-P-K-S system, adds a fourth number for sulphur. 

If some specialized elements added into the NPK fertilizers, such as NPK 16-16-16+MgO, it means he NPK fertilizer contained the

component of MgO.