It's an interesting issue. Factors influencing the capability for
biochar to assist with soil fertility appear to include what the char is
made from and the process that has been used to make the char. Making it
from chicken manure will tend to produce a char that has different
initial nutritional characteristics compared to making it from wood.
Different pyrolysis techniques will produce chars with different
structures and different quantities and types of volatiles. Some of
these volatiles appear to be nutritionally useful. Others may not be
useful and may even be harmful. There's quite a bit of work underway in
this area. (There's still how to get it in the ground economically in
no-till broadacre farming environments but that's another story.)
I found a study a while ago of sites in the northern Pennsylvania region
- which may be the one Mark refers to below - that found substantial
remaining contamination many decades after silvichemical plants closed.
These plants typically used pyrolysis and chemical extraction techniques
to obtain valuable chemicals. I haven't dug into whether the particular
techniques used led to PAC's the bugs find difficult to digest, or
solvents used have sterilised the area, or if the sheer volume of wastes
have overwhelmed the bioremediation capacity. Certainly forests spring
back from the witches brew of chemicals made in a wildfire
Cheers
David
------------------------------
Message: 4
Date: Sat, 17 Dec 2011 19:25:47 -0800
From: "Mark Ludlow"<[email protected]>
To: "'Discussion of biomass pyrolysis and gasification'"
<[email protected]>
Subject: Re: [Gasification] gasifier type updarft use rice husk
Message-ID:<[email protected]>
Content-Type: text/plain; charset="us-ascii"
Jeff and...
There's a lot of different opinions on the value/harm of the "tars" in the
soil. My instinct says "no-no!" but some people drink the distillate and
think that it is God's blessing!
If we observe natural phenomena, for instance forest burns (which,
presumably, have multiple regimens of combustion, from hardly-at-all to pure
ash) we see that there is usually a strong recovery after a burn, but the
ecosystems are usually not replaced, intact, but forced to begin their long,
progressive cycle once again.
A study of 19th-century charcoal kilns in the Eastern U.S., show that there
is a lasting effect on the sites on which they were located. On the other
hand, many suggest that the aromatic compounds produced during pyrolytic
combustion are valuable components of the signaling network that tells seeds
and the soil ecosystem that the sky has opened and that the system has an
altered competitive structure.
Maybe a little is good; and a lot is bad. But despite the evidence that many
of the polyaromatic hydrocarbons remaining in the char produced for biochar
applications is carcinogenic, some certifying bodies have declared it
"Organic" and suitable for unrestricted use in agricultural applications.
Who knows?
Best, Mark
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