[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 
other plants.

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 
> exchanges.
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