On Mon, 10 Mar 2003 15:20:52 +0000 (UTC),
(Victor M. Martinez) wrote:

Terry Horton wrote:
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.

And the same acids are readily neutralized by the soil.

And more is exuded. Plant roots actively maintain a lower pH
microclimate in the rhizosphere. In fact the zone immediately around
the roots is quite different from the surrounding soil. Sugars,
enzymes, amino acids, lipids, all manner of compounds are "oozed" into
the adjacent soil.

Plants are not just passive recipients of whatever is in solution
around them. They in effect chemically "mine" surrounding minerals,
and feed other organisms in return for a supply of water and minerals

I'd agree there is
a state of flux, but I'm guessing the overall balance remains neutral.

Depending on where it and how it was measured... an plug of our soil
would show a pH of 8-9. A few microliters next to the root tip might
be 1.5-2 points lower.

point the owner has to begin the process of removing more phosphorous

If the P available is not bio-available, then the plants will suffer from
lack of P. But you know this.

Are you seeing evidence of P deficiency?

from the soil than is being applied, or suffer increasing problems
from P in the long run.

So how do you propose dealing with the fact that the P in the soil is not
available for plants to use? Acidify the soil? That ain't gonna work.

Anything that produces hydrogen will temporarily acidify the
*immediate* soil microclimate. But sulfur, etc. aren't the answer
imho.

It's a tough deal for west Austin. We all wish there were win-win
answers, but there aren't. At this point the best recommendation is
to use low P, slow release organic fertilizers like those already
mentioned in this thread.

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.

I fail to see how that would make existing P available for the plants. Am
I missing something?

It's well established that even low level of P fertilizer reduce or
eliminate mycorrhizal activity. One of the most dramatic effects of
mycorrhizal colonization is increased P uptake, which they take from
the large pool of "unavailable" P.