On Fri, 7 Mar 2003 16:10:57 +0000 (UTC), (Victor
M. Martinez) wrote:

Yes, but it while it may be toxic levels, it is not toxically available unless
it is met with other elements.

It is not available, period!

Well, yes and no. :-) Phosphorus is in constant flux in soil (a
single atom of phosphorus could be available and unavailable to the
plant several times a day). Roots hairs exude acids that solubilize
nearby phosphates.

While there might be an excess of phosphorous,
that doesn't mean plants don't need bio-available phosphorous to thrive.
Our plants respond great to bone meal. I'm sure if we test our soil it would
be high in phosphorous.

I don't see where more P can ever be a solution to high P. At some
point the owner has to begin the process of removing more phosphorous
from the soil than is being applied, or suffer increasing problems
from P in the long run.

One interesting question (at least to me :-) is why is there so little
bioavailable phosphorous in the first place. My own conjecture is
that it may be due to the impact of our soil cultural practices on
root mycorrhizal fungi.

Almost all plants in nature maintain and have evolved to take
advantage of mycorrhizal associations (myccorhiza - symbiotic soil
fungi that provide water and minerals to the plant in exhange for
sugar and protein). A primary mineral made available by mycorrhizae
is phosphorous.

Conversely mycorrhizal colonization and growth are inhibited by even
high-moderate soil phosphorous (and a number of other nutrients and
lawn/garden chems). Applications of P can even kill plants with
established mycorrhizal relationships. So as we use more and more
exogenous P the soil flora continues to decline, and natural soil
cycling of P decreases. The plants become largely dependent on
frequent high doses of externally applied P. Fe and Z soon become
unavailable, so we supplement those too. On and on...

Perhaps an effective treatment for high P would involve removal of
grass clippings and leaves followed application of a low-P organic
fertilizer. Synthetic fertilizers and compost (which tends to be
poorly analyzed but in general relatively high in P) would be avoided.