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Re: Methods for assessing compost tea quality
The routine soil tests for P and K currently performed by public and private
testing labs have an excellent track record as predictors of plant response
to P and K inputs. These tests are only measuring a small amount of the
total P and K in soil. Routine soil tests for extractable N are generally
not performed because of the lack of predicative ability of these tests.
If there is little relationship betwen plate counts of compost teas and the
disease suppression and plant growth promotion effects of compost teas, then
plate culture should *not* be used for evalating the quality of compost
teas. The same thing stands true for microscopy methods.
In addition to being predictive, methods used for routine testing need to be
cheap and rapid. Is there a method for evaluating compost tea currently in
use that meets all 3 of these criteria ?
Tea #1, sprayed on the plants with the same sprayer as used for tea >#2,
only covered 27% of the leaf surfaces with bacteria and bacteria >alone.
Tea #2 covered 87% the leaf surfaces with bacteria and 5% with >fungi.
Do you have an explanation for why Tea #1 was much less effective in
providing "coverage" of leaf surfaces than Tea #2 ? You indicated that both
teas contained high levels of bacteria.
How does your lab measure leaf surface coverage ? Considering that
microorganisms rarely cover more than 5-10 % of root surfaces (I think this
is generally accepted in the literature), 80 % coverage of foliar surfaces
seems very high...
Let me close by saying that I really appreciate your efforts as well as the
efforts of other members of the vangaurd of practical soil food web
Skepticism (concerning compost teas and other novel agricultural
technologies) is my professional responsibility... I am actually very
optimistic about the future of compost based technologies for promoting crop
root and foliar health.
Dept of Soil Science
NC State University
(919) 515 - 4270
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