What is NPK?
A fertilizer is any material of natural or
synthetic origin that is applied to soils or to plant tissues to supply
one or more plant nutrients essential to the growth of plants. The three numbers on fertilizer represents the value of the three macro-nutrients used by plants. These macro-nutrients are nitrogen, phosphorus and potassium (NPK for short).
Macronutrient fertilizers are generally labeled with an NPK analysis, based on the relative content of the chemical elements
nitrogen, phosphorus, potassium that are commonly used in fertilizers.
For example,the fertilizer urea is labeled 46-0-0.