I see very little on this site about not fertilizing when soil test show not to. I've found that the P and K on most existing lawns show > 30 ppm for P and > 250 ppm for K. Seem to me that most think of feeding the lawn NPK rather than making sure that the soil and application meets the needs of the plants on the property without a lot of waste. Is it more of a selling thing rather than anything scientific. In farming we go very much beyond what is needed for the healthy appearance of plants. We go into an hidden area that landscape fertilization would not even need be concerned with...for yield rather than appearance. I wonder if anyone even knows the soil's weight in 1000 square feet of soil 7" deep to figure what is needed.