Good Morning Fellow Compost tea enthusiasts. Just a note of
introduction. I'm Joel Reiten, Seed Production Manager for Bejo Seed
Company. I am responsible for the conventional as well as organic
seed production for our company in the US. I have been involved in
compost teas for around 7 years now and have met many of you and hope
to meet the rest of you in the future. I'm definitely a lurker at
this site as I am at many during the growing season. Now that I have
had a chance to review some of the messages on the different compost
and compost tea websites I am somewhat angered and very disappointed
at some of the comments and the one sided miss –information that
seems to permeate some of the messages. This response was spurred on
by two organic growers that I work with who forwarded me some of the
e-mails for comment. And no, as some of you might wonder later,
neither grower is connected with Growing Solutions Inc or BBC Labs.
I do not hold an advanced degree in microbiology, my education is in
animal science and genetics, but it is my job to know all of the
facts (or opinion) of experts that work in the fields of
microbiology, and as of late industrial fermentation. I grapple with
the status of a study, that has not been published in a peer reviewed
publication or run thru the academia statistics mill and make the
decision on how much is fact and how much is opinion. So what I am
going to say here is my opinion based on what I consider fact.
First let's talk about the study that Vickie Bess (I'll leave the Ms.
Out) and her staff did at BBC Labs. How many of you actually read the
entire paper? I thought the paper was pretty thought provoking and
did show what microbiology textbooks and industrial fermentation
experts will tell you. E coli can live and grow in an aerobic
environment and that it prefers a simple sugar nutrient source. It
also indicated what may happen in a mixed microbe culture loaded with
simple carbon sources.
The accusation that the study used un-composted material is
unfounded. The facts that I have are that the compost in question
went thru the complete composting regime and was tested before sale.
The tests turned out positive for E. coli and the compost was not
sold as compost. The assertion that properly made compost will not
contain E. coli is also unfounded. The composting process is a
sanitizing process not a sterilization process and unless you produce
your compost in an enclosed environment there is always a chance for
contamination.
How about the oxygen levels reported in the study. Again a lot on
conflicting information. Are the oxygen levels that were reported by
BBC labs possible? Yes, without question. The graphs and charts from
the USGS have been cited as the highest possible levels of oxygen
that can be held in water at a certain temperature and pressure.
Without getting too technical I'm going to say that this is true, but
only to a point. These numbers would be considered the high end
of "normal" like a healthy lake. Numbers that are higher than those
from the USGA chart are considered super saturated. Be careful with
this word. Just because water is supersaturated does not mean it will
oxidize organic compounds. It simply means that it is carrying more
oxygen than would be normal for water at that temp and pressure.
Without question water that is carrying extremely high levels of
oxygen are harmful to aquatic life and microbiology but super
saturation in of its self does not equal harmful conditions.
The oxygen transfer from air to liquid is primarily affected by the
interfacial area of the gas bubble. Increasing the interfacial area
can increase the oxygen transfer rate into the fluid. Increasing the
interfacial area can be accomplished by increasing the aeration rate
and decreasing the bubble size. The fine bubble diffuser plates that
Growing Solutions uses in its brewers is extremely good at producing
very small bubbles at various rates of air flow. The factors that
affect how much oxygen can be "forced" into the water is based on the
amount of pure O2 in the air as well as the pressure that the air is
under. This pressure effect does not mean that the entire vessel
needs to be pressurized; it can simply mean the hydrostatic pressure
at the base of a column of liquid. Combining all of these factors
together these numbers are well within limits. I also had a
biochemical engineering collaborator look at the oxygen transfer rate
as well as roughly calculate the steady state relationship between
oxygen uptake and oxygen transfer based on a high population of
respirating bacteria growing in a simple sugar based liquid medium.
Based on the air diffusion plates used in the System 25 at the time
of the tests and assuming that all of the equipment was working
within manufactures specs, anaerobic conditions very likely did not
occur and the high oxygen levels were within reason.
Other BBC lab thoughts. Plate counts vs. direct counts. BBC Labs
uses the plate count method of evaluating soil and tea microbes. You
can go to their site to read about their different classifications.
I'm not going to debate the usefulness of one over the other but I do
feel that plate counts have their place. You can pick up any good
microbiology text and find a long list of usefulness and short
comings of both methods. Check out Brock Biology of Microorganisms
9th Ed., M.T. Madigan, J.M. Martinko, J. Parker, (2000) Prentice-
Hall, New Jersey.
The problem with direct counts is that you are counting lots of cells
but you are not really sure what they are for the most part. They can
be good bugs or bad bugs. I am very hesitant with direct counts for
tea brewers because the microorganisms have been exposed to a medium
that is greatly different than they would experience in the soil. The
liquid environment in a brewer, loaded with many times the simple
sugars that are found in soils, is bound to shift the populations of
microbes. Plate counts use soil extract agar or artificial media that
closely mimic the amino acids, growth factors and other chemicals
found in the soil, but it is also very low in simple carbon sources,
as is usually the case in soils, so the growth of the microbes on the
culture media is slow and the colony size is small. The conditions
that the media is cultured at will influence the outcome to some
extent, but think of the wide range of environmental conditions that
exist in the soil profile over the seasons. It's impossible to
culture for all conditions and the conditions in a brewer hardly
mimic the conditions in soil.
A legitimate question with plate counts is that the number of
microbes counted is usually lower than in direct counts. Is this
difference in numbers dead cells or cells that are non-culturable?
But both methods are based on dilutions and the numbers can be
mathematically calculated to represent true numbers in the soil or
tea. I personally feel that in a short time newer methods like enzyme
reaction analysis or DNA probes will allow us to come up with more
accurate numbers and will allow us to come up with a better idea of
true diversity in a natural environment. I also personally feel that
in a situation where I am working with biologically healthy soils
that plate counts are more useful to me because I am trying to gently
coax soil microbe populations in a certain direction and I need to
know if I am doing so down to the genus and species.
There has also been the assertion that the species richness diversity
index (SRD) that BBC Labs uses is incorrect and does not exist in the
literature. First of all an index is a way to reference the
relationship between sets of data, like species richness and species
diversity. There are lots of examples of such indexes in published
ecological research and well as a number of software programs to
calculate these indices. An oldie but a goodie is the Simpson's
Index, Simpson, E.H. 1949. Measurement of diversity. Nature 163:688.
Since 1949 this index has been broken down and defined in several
ways but is an index of species richness and diversity. An index that
I am working with is the Shannon-Wiener index. This index shows a
relationship to species richness and diversity but it measures the
order, or disorder, observed within a particular system. If you want
to delve into the math it is also easy to see how negative numbers
can come into play if the population falls below a set level. I am
not privy to the math behind BBC Labs methods of calculating their
SRD numbers but I believe that they have a factual basis and can be
related to the soil food web. Other references are Peet, R.K. 1974.
The measurement of species diversity. Annual. Rev. Ecol. Syst. 5:285-
307. and Krebs, C.J, 1989. Ecological methodology. Harper and Row,
NY.
Thoughts on Brewers.
Great discussion about types of brewers in this group. The bottom
line is that there are lots of brewers available or you can build
your own depending on your situation. The technology behind the
aeration of water and the culture of microbes in a liquid solution is
well documented and not rocket science. The exact science behind the
culture of extremely diverse microbes from their extraction to their
growth and development is however a bit more tricky. I'm not sure how
comfortable I am with trying to culture both bacteria and fungi at
the same time in the same container. They have different growth rates
and different nutrient requirements that include growth agents that
may not be in the same amounts or ratios in compost than they are in
the soil. Mixed populations also tend to excrete toxins that if not
monitored and removed can affect the population diversity with a
brewer.
Let me stress however that if you use good quality compost and if
you have a vigorous enough activity within the vessel, you will sheer
the microbes out of the compost and get them into solution and you
will get good numbers both by direct counts and by plate counts of
all of the components of a good soil food web. If you are using
compost teas on biologically inactive soils or in soils that have
been chemically abused you will more often than not get good results.
If however you want to use compost teas for a more specific reason
then I think you need to know a bit more about the specific types of
organisms that you want to culture and how to encourage their growth.
Brewing nutrients.
This discussion could go on for days. I'll be at the Eco-Farm
conference and will talk about nutrients in teas but here is a
summary. I do not think that the addition of large (disproportionate)
amounts of simple sugars as carbon sources are the correct way to
brew good ( highly diverse populations that mimic the natural soil
populations) compost teas. If you look at the carbon sources in the
soil they include amino acids, organic acids, pentoses, hexoses,
pyrimidines, puridines, vitamins and many other organic enzymes and
growth factors. High levels of simple sugars give preferential
treatment to some bacteria and a few fungi to the detriment or
exclusion of others. After a great deal of research I prefer Growing
Solutions catalyst food source because it has very low levels of
simple sugars and its very diverse level of more complex carbon
sources and growth factors that result in a tea that is more
representative of the microbes in a natural soil food web. Is this
good enough? No, I think that much more work needs to be done on food
sources as well as buffering agents, paying attention to osmotic
conditions and perhaps running our brewers on a more continuous basis
rather than as a batch culture.
Biofilms. I saw a post that stated that biofilms were a sign of
anaerobic activity. This is a new one on me. You can find biofilms on
nearly all surfaces that are exposed to a biologically active liquid,
aerobic or anaerobic. Bio-films are not difficult to remove if you
get to them before they dry. Biofilms make great glues!
E-coli and the NOP. I left these comments until last knowing that a
few diehards would slog thru this long post. E. coli and the question
of food safety is a hot button topic at the present time. I'm
certainly not going to downplay the significance of the danger of E.
coli O157:H7 if ingested. But I do believe that the danger has been
blown a bit out of proportion particularly when it comes to compost
teas.
Let's look at the facts. Physiologically E. coli is versatile and can
adapt too many environmental habitats. It can grow on media with
glucose as the sole organic ingredient. Wild-type E. coli has no
growth factor requirements and can metabolically transform glucose
into all of the macromolecular components that it needs. The
bacterium can be grown in the presence or the absence of O2. Under
anaerobic conditions it will grow by means of fermentation but in
aerobic conditions it has the ability to switch to an alternate form
of respiration that utilizes NO3 and NO2 for its respiratory electron
transport processes. In part this is why E. coli can adapt to
anaerobic (intestinal) or aerobic (surface contact) conditions.
I can find no references where it has been demonstrated that in a
mixed culture E. coli is eliminated by other microbes. I do agree
however that E. coli growth can be reduced to nearly 0 if its food
source is reduced and if the mixture contains high levels of a
diverse population of other microbes.
I believe the course of action for the NOP is straightforward.
1. Use properly prepared compost for application as a solid or
as a liquid such as compost tea.
2. No raw manures within 120 days of harvest.
3. Compost or compost teas used within 120 days of harvest must
have a documented negative E. coli test.
With the availability of rapid E.coli tests that the water treatment
field uses, these tests can be included in the organic
farm management plan and part of the inspection can include a
demonstration that the farmer knows how to use the tests.
The future of compost teas is very exciting. I will continue to use
compost teas as an important part of my organic farm management.
Much work needs to be done to continue to bring the use of compost
teas into the fold of truly useful techniques that the organic and
conventional farmer and horticulturists can use to build healthy
soils and combat plant diseases. To this end the divisiveness of
ridiculing a person or a business because they do not conform to one
persons ideals is detrimental to the openness and continued
advancement of this young and growing industry.
PS The paper describing my work with compost teas for the control of
Xanthomonas is now ready. You can request a copy or you can read it
in the OR Tilth paper next month.
All the Best,
Joel
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Received on Mon Nov 04 2002 - 17:37:09 EST