[Terrapreta] re Cameron Smith has some questions

[teelws at jmu.edu]

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