If it is true that P does not unlock from the mineral soils over time, with the aid of AM Fungi and other microbials, then can it be said that lawns do not require P applications, except as a starter fertilizer for new seed??? The following article states: http://www.plantphysiol.org/content/156/3/1050.full ... AM fungi grow extensively in soil to form a well-developed hyphal network that absorbs Pi (via fungal high-affinity PiTs) from up to several centimeters from the root surface and can markedly extend the depletion zone (Fig. 1). P is translocated rapidly to the roots (probably as polyphosphate), overcoming the slow diffusion that occurs in the soil solution. The individual fungal hyphae have much smaller diameters than roots, allowing access to narrower soil pores and hence increasing the soil volume explored (Drew et al., 2003; Smith and Read, 2008; Schnepf et al., 2011). These factors are the major cause of increased P uptake and positive AM growth responses. ..." So the point here is that the AM Fungi is out there actively getting 'available P' from the soil more efficiently than simple root hairs can... All this amounts to,, is that the AM Fungi can more thoroughly deplete the depletion zone of the available P... There is doubt that AM Fungi can actually retrieve some of the 'unavailable P' that is also unavailable to root hairs alone... Is there a legitimate reason for gov't to 'outlaw' P for lawns stating that the lawns don't need it, anyways???