Nitrogen (N), phosphorus (P), and potassium (K) are the main nutrients that plants need to survive. Complete fertilizer contains those three ingredients and they are listed clearly as the N-P-K ratio. So, if a package of fertilizer states that its N-P-K ration is 10-6-6, then the fertilizer contains 10% nitrogen, 6% phosphorus, and 6% potassium. Water-soluble nitrogen satisfies the plants needs quickly, while insoluble nitrogen must be broken down by organisms in the soil before the plants can be fully satisfied.