Every bag of fertilizer has at least three numbers on it. The number represents the percentage of each element in the bag.
The first number (N) represents the percentage of nitrogen; the second (P), the percentage of phosphorus; the third (K) number represents the percentage of potassium. These nutrients are called the macronutrients.
Some fertilizers contain smaller amounts of what are called secondary nutrients. These are: calcium (Ca), magnesium (Mg) and sulphur (S). Micronutrients, which are needed in very small numbers are: iron (Fe), manganese (Mn), zinc (Zn), boron (B), copper (Cu) and molybdenum (Mo).
