Not all fertilizers are created equally...
Beyond the analysis of the Nitrogen-Phosphorous-Potash numbers, there is the need to understand how the inorganic or organic chemicals are processed by one's soil.
First, a distinction about organic and inorganic lawn fertilizers... The organic group promises to be healthier for the soil, offer more long-term soil benefits, and have less or no harmful salts. The common products are Milorganite-brand name and (newer) chicken manure. They may cost more and have less nitrogen production. Nitrogen, as you may know, creates the greening of the lawn. Still, adapting to this product type may have preferred long-term soil and lawn benefits.
Most lawn fertilizers you'll find at your garden center are from inorganic chemicals. To get maximum results from your choice of fertilizer, you should look for the "W-I-N" percentage, or water insoluble nitrogen percentage. A high "W-I-N" number is preferred--it equates to the lasting application of nitrogen being applied to the soil and lawn. In other words, it is being used more slowly by the soil; you'll get extra weeks of greening.
An example of an un-named product and sample chemical is shown here:
(Article content solely that of Dan Bonner, horticulurist and garden enthusiast, 2009.)