[compost_tea] Toxins that Affect Worms and Soil Microorganisms - how to identify and correct?

From: chris reid <reidchris_at_earthlink.net>
Date: Sun, 16 Nov 2003 13:46:36 -0500

Elaine Ingham said:

If you don't see the conversion happening (green plants without fertilizer
additions, and reduced need for water) within the first year, suspect a
serious residue of toxic chemicals in your soil. It is the biology which
will decompose those toxics, but you have to figure out what biology is
needed first.

Elaine and all,

I would like to be able to recognize landscape situations that are likely
sources of toxic chemical residues at the outset, so I can begin to address
early on the problems that cannot be addressed by compost tea (or at least
be able to help the customer understand what we're dealing with and what to
expect).

I have begun to look into what's toxic to earthworms, because there are so
few in the rose garden I'm converting from conventional to organic. First,
the soil pH was low (5.1 in one bed; 5.4 in another) and it's now tested at
6.3 and 7.1 in the top 4 inches of those beds. The garden was unmulched, so
mulched with 3 inches of partly decomposed leaves. I thought I'd see all
kinds of worms under the leaves, or at least castings, but no, I don't.

So I started casting about (no pun intended) for info on what is toxic to
worms. Found out that copper fungicides are toxic to worms, and can cause
accumulations in the soil which may show up as stunted plant growth or poor
root growth. Since it's used for powdery mildew and roses get powdery
mildew, a possible explanation is copper. The example in the article about
earthworm toxicity was from the experience on citrus farms, which frequently
use copper based fungicides.

Zinc is also toxic at some elevated level to worms, and is used in some form
in Mancozeb. Don't know if Mancozeb is considered toxic to worms.

Quote from another article: "The copper based sprays are also used to
control fungal attack, but Bordeaux Mix and Copper oxychloride will wash
from your plants into the soil, where the residues kill your earthworker
worms. Kocide (Cupric hydroxide) does not kill worms as other copper sprays
do, but it’s pretty expensive." Source:
http://www.greenfingers.com.au/services/seasonal_tips/2002/june/24_june_2002
.htm

also found that Benomyl is earthworm toxic. Benomyl should be a lot less
persistent than copper, though, and I think soil biology could handle this
toxin.

Perhaps at some point earthworm color may be useful to determine what's in
the soil, though the example in the attached link - worms changing color due
to aresenic in the soil from a nearby mine -- has to do with extreme levels
of toxic substances: http://www.nature.com/nsu/030224/030224-5.html

I'd be interested in the methods available to identify or preventatively
address potential toxic levels of pesticides in soil, both laboratory or
field methods. Is anybody trying to systematically consider this aspect of
what's going on in the soil?

Chris Reid




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Received on Sun Nov 16 2003 - 14:20:53 EST

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