Sometimes you may want time release, but most of the time you can go to the co-op and pick up regular NPK fert and use that. Milorganite and such is good too, for lawns.
The most important thing is to know when and how much a lawn needs and applying it accordingly. If you chose the over-fert 6 step program, be sure it is on over-watered lawns. Constant additional NPK apps during a relatively dry summer will cause dieback due to N burn.
Now that I know that clay's texture(platelets) has nothing to do with water infiltration, percolation, or drainage,,, I wonder what does...