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Old March 10, 2012   #12
dice
Tomatovillian™
 
Join Date: Jan 2007
Location: PNW
Posts: 4,743
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The question is how much 13-13-13 per plant. Raising the phosphorus
above about 50 ppm in the soil inhibits mycorrhizae, until it disappears
completely at around 100ppm.

I do not know how you find what the P ppm in the soil will be after adding
a particular amount of 13-13-13 without a lab handy to test. (I have seen
this formula with 13-8-13 recommended for the N-P-K part, too.)

Older style agriculture from decades ago ignored mycorrhizae and most
soil organisms. "Organic" was not an issue, etc. If they had soil disease,
they would blast it with methyl bromide (kill every organism in it) and
then supply enough N-P-K to grow plants in pure sand (just add water).
13-13-13 seems more like a fertilizer from that era than something that
is going to fit well with organic gardening and mycorrhizae.
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