Fertilizer is simple once you know the letters and numbers. N-P-K are the big letters on the bag and they stand for Nitrogen (N), Phosphorous (P), and Potassium (K).

Under the letters are numbers. which stand for the percentage of weight of each element in the bag.

                                                                  N      P      K

                                                                 12      8      16

If it is a 50 pound bag, there is 6 pounds (.12x50=6) of N, 4 pounds (.08x50=4) of P, and 8 pounds (.16x50=8) of K. Once the amounts are known then an application amount can be figured and you know if the fertilizer on sale is really a good buy. Those numbers never add up to 100%.

N,P, and K are called macro-nutirents. There are also many micro-nutrients but unless there is a real problem, they shouldn't be a concern. If there is a real problem then a detailed soil analysis by a professional is the solution. With that said, there is one exception that is iron (Fe). High desert soils are always iron deficient so that micro needs to be applied on a regular basis and many fertilizers have iron added. Many companies make many different mixes but there are only two speeds, fast (soluble) and slow (slow release). Slow release costs a little more but can't burn the grass.