North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

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.