[NAFEX] P availability

Alan Haigh alandhaigh at gmail.com
Sat Jun 20 11:55:07 EDT 2009

Richard posted, "my county agents office has always taught that P was rather
immobile. Now that doesn’t say anything about whether it is available for
plant uptake or not. If very immobile, I would question its availability to
plants to absorb it".

My answer is that it is estimated that on average, 15% of applied P is taken
up by plants before becoming immobile in commercial agricultural
application.  I've no idea if there is a wide range to that stat in relation
to various crops.

For trees it used to be suggested that P be applied into holes made by a
crowbar to get P close to the roots.  Seems this wasn't actually helpful and
the practice is no longer recommended.  I'm aware of no research that
indicates an advantage to any kind of deep-root fertilization and at one
point I made an effort to find such research.  But that was before the age
of computers- Google deep root fertilization, anyone?

Tree spikes are a remnant of this misconception about trying to get
fertilizer close to the roots.

The greatest benefit of mychorizal associations is the ability of the fungi
to deliver adequate P to trees in soils with deficient amounts in soluble
form.  This has been discussed here in detail in recent exchanges.
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