Having a healthy soil with plant friendly, root friendly structure, is the most important part of plant husbandry. CEC, pH, water practices etc, are the limitting factors of nutrient useage, as Kiril suggestted. Many lawns are like the stranded lifeboat in the middle of the ocean. Surrounded by water and dying of thirst. Not utilizing P - is a good exa. of how AMFungi works to balance out problems in certain situations. That relationship epitomizes the essential concept of - one way - in which, organic principles apply. Is you mix paint and decide it needs more yellow... you add yellow... problems solved. When you ferilize soil and decide it needs more P... you add P... problems solved temporarily at best. Many times problems continue and sometimes worsen. Were you aware that very few soils are actually deficient in P for growing turf? that, Most soils have an abundance of P?