[NAFEX] phophorous availability
Road's End Farm
organic87 at frontiernet.net
Sun Jun 21 17:09:00 EDT 2009
It's my understanding that some crops, in particular buckwheat, are
capable of taking up P from the soil even when it's in a form not
available to most plants; and that using such plants as a cover crop
(tilling them back in) can then provide that P in a form available to
I did a very fast search and found a number of references to this; one,
though it didn't go into any detail, sounded as if the buckwheat might
be doing this along with fungal associations, though I hadn't heard of
this aspect before. No time right now to look into it further.
Finger Lakes NY; zone 5 mostly
On Jun 20, 2009, at 11:36 AM, Alan Haigh wrote:
> 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 becomming 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 computors- 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
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