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Re: Species diversity
As I stated in my previous post, I completely agree that plate counts are
not a very useful research method for evaluating total or active microbial
My point is that for routine testing purposes (i.e. which require rapid and
cheap methods) I think that a plate count method may have value for routine
assessment of the functional value of compost teas.
This is my hypothesis. I have not personally tested this hypothesis.
Hopefully any labs using plate count methods to evaluate the quality of of
compost teas have tested this hypothesis.
The connection between nitrate and plant uptake and response is easy >to
see, because nitrate is so soluble and so mobile.
This is not accurate... very few soil testing labs analyze (routinely) for
nitrate because the relationship between levels of nitrate in soil samples
(collected before the growing season) and crop response is normally very
weak. There are some exceptions such as PSNT (where samples are collected
immediately before a rapid phase of plant growth) and also in arid regions.
But this isn't the case for P, for example.
There is plenty of evidence that routine soil tests for P frequently have
good ability to predict crop response to P inputs.
The Melich 3 (and other extractants used commonly for routine soil testing)
do not extract the exact pools of P (or other nutrients) that are used by
crops during a subsequent growing season. The Melich 3 extractant simply
extracts a quantity of P that consistently allows prediction of need or lack
of need for additional P.
Just as routine tests for soil nutrients have value despite not revealing
the full range of pools of nutrients that may be accessible by crops (or the
mechanisms by which these pools are accessed), I am suggesting that a
routine test of compost teas (using plate counts)
may have predictive value despite only presenting a small window into the
biodiversity of compost.
Mycorrhizal fungi, for example, cannot be cultured on any plate medium.
That seems a huge set of beneficial organisms that are completely missed by
This is not true - the literature contains lots of evidence that that plate
culture of ectomycorrhizae is possible and is a useful scientific method.
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