Posted: 15/06/2015 at 18:40
My neighbour killed half his lawn with overapplication of Iron sulphate. I recommended sharp sand to improve drainage when spiking to aerate and decompact but he came home with a big bag of lawn sand, applied all of it and was left with a few patches of grass.
It often looks like one has killed the grass but after a week or so it greens up. It it does not, set your blades high keep trimming, keep dethatching too let the light in, keep aerating (spiking) it and the healthy grass plants should still send out stolons (lateral rhizomes) and start new stems.
Don't water the lawn that'll just dissolve more into the roots. If it rains it rains, you can't do anything about that.
If you have access to a hover mower with grass collection that may well suck up undissolved granules. It's worth a try.
I use only, erm, self-made nitrogen fertiliser.