[Terrapreta] Now: Biochar v. humus

[Mark Ludlow]

Thank you, Wayne!

I appreciate your explanation of the interdependence of external conditions
and soil structure.

You say that: "Humus is stable in soil in some places." But then you suggest
that the stability refers to a terminal % in the A horizon (in a particular
system). Are you suggesting that humus is stable over time or that
generation and consumption reaches an equilibrium in undisturbed soil?

I understand the permanence of char. Prehistoric cave art executed with
charcoal is still vivid after 30,000 years. But is char a singular solution
to soil fertility and C sequestration in temperate climates, or should we be
considering a hybrid solution that includes humus as well? I was taught
(somewhere!) that humus is relatively immune to microbial digestion (nothing
was said about termites). It also shares or exceeds biochar's CEC, if I
understand things correctly. I don't know about the comparative conversion
efficiencies of labile carbonaceous material into humus versus char. Can you
shed some light on this?

Thanks, again.

Mark

-----Original Message-----
From: teelws at jmu.edu [mailto:teelws at jmu.edu] 
Sent: Saturday, June 28, 2008 4:26 AM
To: mark at ludlow.com; terra pretta group
Subject: Re: [Terrapreta] re Cameron Smith has some questions

Mark and All,

Just a quick comment on biochar and humus stability in soil.  As is common
in science one answer you must expect is that it depends on conditions.
Humus is stable is soil in some places.  In the dry tropics termites
eliminate most of it.  In the wet tropics intense soil biological activity
eats most potential humus sources before they have a chance to develop into
humus.  Biochar is stable in the presence of termites and wet soil
biological activity.  The only real question is how long, and the best
answer is "thousands of years" with no real data giving much more specifics.

In temperate zones, in stable conditions, humus levels build up in time to
relatively stable levels in the neighborhood of 4 to 6% by weight of the A,
or surface horizon of the mineral soils.  (The O-horizon can be significant
in some areas and of course has a higher percentage organic matter, but this
is mostly in undisturbed areas with moist conditions.)  In natural systems
this percentage remains at equilibrium, but if you disturb the soil, as is
the case with most agricultural activities (or in clear cutting forests)
increased soil oxygen and biological activity, both from the disturbance and
increases in nutrients through fertilization, reduces this humus component
significantly.  Since humus, or soil organic matter, is often the primary
holding area for soil nutrients, aside from the high cation exchange
capacity clays like montmorillinite, illites or smectites, soils become less
fertile.  Adding biochar increases this nutrient holding capacity and
hopefully decreases th!
!
e need for fertilization because it will reduce nutrient losses due to
leaching.  However, we do not have evidence of the efficacy of biochar in
all soil types and conditions.  That is why the testing of biochar by
members of this list is important.  

Humus is not stable in the sense of long lasting at the molecular level.  It
is stable to an equilibrium point, variable by soil type and climate
conditions, if the soil is not disturbed.  It is constantly made and
destroyed by the biological activity native to the ecosystem of a particular
place.

Wayne 

---- Original message ----
>Date: Fri, 27 Jun 2008 23:48:44 -0700
>From: "Mark Ludlow" <mark at ludlow.com>  
>Subject: Re: [Terrapreta] re Cameron Smith has some questions  
>To: "'Reid, Keith (OMAFRA)'" <keith.reid at ontario.ca>,
<biochar-ontario at googlegroups.com>, "'Jeff Berg'" <jeffberg at rogers.com>,
"'Cameron Smith'" <camsmith at kingston.net>
>Cc: "'Douglas Prest'" <doug at douglasprest.com>, "'terra pretta group'"
<terrapreta at bioenergylists.org>
>
>   Hi Keith,
>
>    
>
>   Will you please compare the relative stability of
>   "forms that are either retained in the soil (stable
>   organic forms)" and Biochar. I have come to believe
>   that fully-developed humus is relatively impermeable
>   to microbial degeneration. Can you, please, speak to
>   the relative efficacy of each? It seems like humus
>   would be much more efficacious in retaining soluble
>   nutrients (in solution).
>
>    
>
>   Best regards,
>
>   Mark
>
>    
>
>    
Wayne S. Teel
MSC 4102 ISAT
James Madison University
Harrisonburg, VA 22807
Tel: 540-568-2798
Fax: 540-568-2761