Subject: Re: Methods for assessing compost tea quality

From: Elaine Ingham <[email-masked]>
Date: Wed, 6 Nov 2002 12:44:02 EST

Sorry, Joel, you were correct.  I was thinking of endomycorrhiza, since I was
focused on row crop plants.

So, now I'm confused about why you brought up extractable nutrients as a good
model for testing compost teas.

If in fact there is little correlation between what can be extracted and
plant growth, then why would the incredibly tiny portion of the actual
species diversity that you can get from plate counts be expected to give you
useful information?

Extraction of the soluble pools of inorganic nutrients from soil gets a high
percentage of those pools.  But if the correlation between the measured
nutrient concentration them and plant growth is not all that clear, as I
think you just objected back to me.

Why is that an argument, then, to suggest that we could use assessment of the
few species of bacteria that grow on plates to be representative of whether a
compost tea is going to be successful as suppressing disease?

I think you in fact argued against the use of plate count approaches.  If we
do a good job of extracting most of a nutrient from soil, and that still
isn't a good way to assess if plants will benefit from that nutrient, why
would an assay, that barely gives us much understanding of the whole
community give us any understanding of the ability of that tea to influence
plant growth?

There are no data showing that plate count information relates to benefits to
plants, as least that I'm aware.  Maybe the experiment that J Reiten will
give us data to show the relationship, but at least so far, there are no data
to show any relationship.

On the other hand, let me summarize an experiment we have finished and are
writing up for publication.  We had ten randomly drawn tomato plants that had
been in a greenhouse where blight was taking over.  So, all ten plants had
equal chance to be infected, and all the plants in the greenhouse succumbed
to blight in the next week.  These ten plants were split randomly into two
groups.  Five plants were treated with Compost Tea #1, and five with compost
tea #2.

Plate counts showed no significant difference between the two treatments.

All five plants treated with tea #1 died of blight within the next week.
None of the plants treated with tea #2 died, and we picked tomato from those
plants for a long time.  We repeated this test, essentially with field grown
tomato at Sunbow Farms.

What was the difference between tea #1 and tea #2?

Direct counts showed us the difference.  Tea #1 had high numbers of bacteria,
no fungi, no protozoa, no beneficial nematodes.  Tea #2 had high bacterial
numbers, good fungal biomass and activity, good protozoan numbers, and some
beneficial nematodes.

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.

So, which way of assessing tea quality do you want to use?

Elaine Ingham
President, Soil Foodweb Inc.
www.soilfoodweb.com

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From: Joel Gruver <[email-masked]>
Date: Wed, 6 Nov 2002 14:25:32 -0500

Hello Elaine,

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 ?

You wrote:

>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
management.

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.

Joel

Joel Gruver
Dept of Soil Science
NC State University
[email-masked]
(919) 515 - 4270

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From: Elaine Ingham <[email-masked]>
Date: Wed, 6 Nov 2002 17:10:00 EST

Hi Joel -

You asked:

Total and active bacteria, and total and active fungi take about 20 minutes
per sample to assess.

We have documented the food web required in the tea in order to see disease
suppression - those results are written up in the Compost Tea Brewing Manual,
in a format that most growers can easily comprehend (not a scientific paper
write-up).

To obtain nutrient retention in the soil, bacteria and fungi are necessary.
To have normal nutrient cycling, protozoa and nematodes (not the
root-feeders, but the beneficial nematodes) are required.

To build soil structure, organic matter, improve water retention, aeration,
ALL the organisms are required.

So, we have the methods to assess all those organisms.  Are they present in
your soil, in the compost, or in the compost tea?  Without the biology
present, we know these broad functions will not happen.

When you talk about functional groups in the soil, it is as if you think that
organisms that grow on plate as active in the soil.

They are not.  Thus, as a method to assess function, plate counts are
pitiful.

As a method to determine whether a functional group exist in soil, again,
plate counts are pitiful, because 99% of the individuals that might be able
to perform a function do not grow on that plate.

If you want to know function, do any enzyme test.  Then you know how much of
that function is being performed right now.

But enzyme analysis doesn't help you to know how much that function will be
maintained.  You can be predictive only if you know the number of active
organisms performing that function now, and in ten minutes, and in an hour,
etc.  Plate counts don't allow you to do that.  Most of the organisms that
grow on any plate are dormant forms, spores, that were not active in the
soil, or compost, or tea.

> teas contained high levels of bacteria.

Tea #1 contained just bacteria,  The number of ACTIVE bacteria, as assessed
by FDA staining, was lower in tea #1 than in tea #2.  Fewer bacteria "stuck"
to the leaves (27% coverage), since they were not active at the time of
application to the leaf surfaces.  Tea #1 was made with a different compost
than the second tea.  Tea #1 had no fungi.

Tea #2 had more active bacteria, had good active fungi as well.   More of the
organisms stayed on the leaf surface.

> is generally accepted in the literature), 80 % coverage of foliar surfaces
We measure organisms on leaf surfaces by looking at the organisms on the leaf
surface.  We stain them, so we can see them against the background of the
leaf.  The staining procedure takes about 3 minutes, and then we can see if
they are present, and how much of the leaf surface is covered.

> optimistic about the future of compost based technologies for promoting

I appreciate the skepticism, as long as you remain convince-able when the
data are in front of you.  There are a number of researchers who dismiss new
approaches because they don't have "enough" data.  To dismiss something
without at least testing it, and testing it fairly, has undermined the image
of researcher in the US.

Elaine Ingham