Thank you Riggle,
IF this post isn't helpful to most, It is helpful to me.
A couple months ago, we laid 80 yds + a little of fescue blend sod to a parcel of lawn that is mostly rock, some silt and 65% shade. We applied 5 1/2 cu.yds. topsoil to the rocky area for a root bed. The area is 30X30.
Fertilizer was not used at the time of installation. A couple weeks after the sod became webbed into the soil, things were well........deep green color,etc. The heat poured on and the color faded fast. Two weeks later, the company that fertilizes this lawn applied 46/0/0 to this blended bermuda / zoysia lawn and evidently the urea got a hold of the fescue. You can imagine that a root probe is useless in this case of rock at such a shallow depth. In my case, the roots don't extend any deeper than at least one inch. If it weren't for the irrigation, this sod would have perished anyway.