Quote:
|
Originally Posted by dice
For inhibition of mycorrhizae growth by phosphorus in the soil
or growing medium, I would expect that one would need the
quantity of phosphorus specified in parts per million (ppm, the
way you see it in soil tests).
|
So, I researched this a little, and I discovered this document
(
http://mining.state.co.us/TechnicalB...orusLevels.pdf ), which says that
mycorrhizae infection of the roots is maximized at around 50 ppm
phosphorus, and above 100 ppm it drops off.
In a document for orchid growers, I came across this online (javascript)
calculator that translates fertilizer N-P-K levels and teaspoons per gallon
(1 tablespoon = about 3 teaspoons) to ppm in the soil or container media:
http://www.firstrays.com/fertcalc.htm
Figure that this is going to be a fuzzy measurement, as what happens
to the phosphorous once it hits the soil or container media depends
on media pH, what other nutrients are already there, what the CEC
(cation exchange capacity) is, and so on. But it can give one a clue
about how much P in how much liquid or water soluble fertilizer
is grossly too much for mycorrhizae to provide any benefit to one's
plants.
It does not help much with granular or pelleted fertilizers, because
they are not added to the growing media in "teaspoons per gallon".
Total PPM of phosphorus would depend on rainfall, irrigation, volume
of container media if using containers, drainage, release rate of
phosphorus from the fertilizer, as well as the other factors mentioned
above. A soil test may specify P in ppm, though, and testing for
available phosphorus at various times of the season may tell you
what the P ppm in the soil is at beginning, middle, and end of season
given a particular fertilizer regimen.
(I just wanted to post the calculator URL. It seems really useful if you
have target ppm levels of nitrogen (N), phosphorus (P), and/or
potassium (K) that you want to achieve and you use liquid or
water-soluble fertilizers.)