You may remember your Grandad mixing his own fertiliser consisting of Sulphate of Ammonia, Dried Blood and Fish and Bone Meal - sounds ghastly and it probably was. It is still possible to purchase straight Sulphate of Ammonia as a lawn fertiliser and good old fashioned Growmore. These age old Nitrogen sources are likely to scorch your lawn, especially Sulphate of Ammonia as it has a Nitrogen content of 21% straight Nitrogen - a generating real flush of growth and then the benefit quickly reduces and is gone.
One important problem of not keeping your lawn topped up with available nutrients is that the lawn disease, Red Thread will quickly appear. You have been warned and there is plenty of it around currently.