Lawn organic fertilizer application. LINKS →
https://www.howtowithdoc.com/lawnorg...
Doc explains the role of lawn organic fertilizers and how they work.  A key element of adding organic matter to your lawn is a healthy soil.  Good microbes and good fungus help our lawns grow and reduce the amount of fertilizers needed.  By adding organic lawn fertilizers we feed the living organisms in the soil. 
The lawn makes organic molecules such as sugars by photosynthesis and supplies them to the fungus, and the fungus supplies to the grass water and mineral nutrients, such as phosphorus, taken from the soil.