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Re: Methods for assessing compost tea quality
Hi Joel -
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 ?
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.
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.
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.
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...
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.
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.
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.
President, Soil Foodweb Inc.