P might be everywhere but it is not everywhere in the same amount and in the same form of availability. The issue with P is mobility and availability. P provided via organic fert to a perennial crop like a lawn is very difficult. P has low solubility so it does not move readily through the soil profile. That is why P pollution of surface water is such an issue. P really needs to be incorporated to the soil. So I would say synthetic P is safer for a perennial crop than organic P, but even P in synthetic fert is not that solubility Mycorrhizae benefits plants by extending the surface area of the soil that the root can mine nutrients this is beneficial for the uptake of immobile nutrients like P. Plants must give up space and Carbon in this relationship in turn for the benefits provided by the Mycorrhizae. If one fertilizes to the point of providing enough P to the plant, the plant does not need this association and therefore there is no benefit in expending Carbon to develop the mycorrhizae relationship. Thus the plant will lose out on the other benefits of the relationship like increase in available water, inhibition of heavy metal uptake, etc. So P does not directly damage the fungus it prohibits the forming of the relationship by providing the needs to the plant without them. P is one of the main issue with organic fert. Plants take up 5-25% as much P as N. Manures contain about 25-50% as much P as N. So to fert with manure based fertilizers based on a soil test N. You will be over applying P, which has negative environmental impact. Remember P does not move through the soil so it is lost via surface water. Surface water makes its way in my part of the country either to The Great Lakes or the Gulf of Mexico. Unlike soil, whose most limiting nutrient is N waters most limiting nutrient is P. So when you add P you see a dramatic impact. It causes eutrophication, which is accelerated growth of algae. This mass algae bloom then dies and decomposes causing hypoxia, as the O2 is consumed by the decomposers. So to say that organic manures are safe alternative because they are natural is incorrect. They need to be carefully applied and managed as synthetic fert. I would argue that in a perennial crop like turf synthetic fert might be more environmentally friendly when used by those than don't fully understand these concepts. One more thing to remember about organic fertilizers like manure. Their source of N is from an animal, whose source of N was agricultural crop whose source of N was a synthetic fert. I am not anti organic, but we cant demonize synthetic fert because it is still a necessary tool. Sorry for ranting.