Actually, phosphorous (phosphate) exists in the soil as an anion and is not held at cation exchange sites. However, instead of being leached out of the soil it forms water-insoluble compounds with other minerals, depending on pH. Phosphorous uptake is 500% or so higher from organic matter than from the mineral soil. Heide Lawrence F. London, Jr. wrote:
I think that is the key to understanding P nutrition and the role of mycorrhizae. P tends to be adsorbed on soil particles rather than in solution.That must be what he told me that I forgot, P adsorbed on soil particles. > Unlike most minerals that are swept up in bulk uptake ofwater by the roots, P does not move much in soil water. The root system must go and extract it. But the root system is not big enough, hence the niche for mycorrhizae, which can intimately explore far more surface area of soil particles than can roots, especially early in the season.
******************************************************** To unsubscribe from SANET-MG: 1- Visit http://lists.sare.org/archives/sanet-mg.html to unsubscribe or; 2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message. Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html For more information on grants and other resources available through the SARE program, please visit http://www.sare.org.