[Terrapreta] charcoal degradation - uncertainties about its half life

[Brian Hans]

Thank you Andrew and Mariska for bring up this very important topic, likely the most important topic that TP should be discussing.
   
  Im not going to cite any ref. material but after a few weeks of discussing TP with various soil scientists, it seems that charcoal can infact break down over time, organically and chemically. It is also easily lost thru erosion and other climate events. I heard serious questioning about the perported lifespan of charcoal in the soil. I also heard the term 'priming effect' but he didnt have a cite... likely from the one Andrew ref'ed. Tho charcoal remains longer than raw bio-mass and has many benefits because of that, there is very little longer term data on this topic and definately more needs to be done. 
   
  To confuse the matter, an activated carbon specialist mentioned to me that hardness would likely determine retention time in the soil, which goes to the feedstock AND quality of process. 
   
  I am convinced that charcoaling is generally better than composting or just letting it rot. But just as compost has a 1/2 life in the soil, so does charcoal. 
   
  Brian Hans
   
  
Andrew Zimmerman <azimmer at ufl.edu> wrote:
  
Mariska - It is generally assumed that charcoal (black carbon) is not very biodegradable because of its chemical composition (highly aromatic, with relatively little nitrogen, etc) and simply because it remains in the soil for long periods of time.  However, recent work (papers attached) has shown that microbes can indeed respire and abiotic reactions can breakdown this material to at least some extent, especially when more labile organic matter is also added (so called 'priming' effect).  In fact, my laboratory has found the same and is currently working on defining the properties of biochar and its remineralization rates better.  -AZ


At 01:21 PM 11/15/2007, mariska evelein wrote:
  Hello List

A problem I stumbled across today is the half life of charcoal in the environment.

No one seems to have rigorous scientific proof that charcoal is inert, but we are all assuming it is.

According to the attached peer reviewed article (new directions in black carbon organic geochemistry, masiello, 2004) there are some serious gaps in how much black carbon is produced yearly and how much of it we find in the environment, suggesting there is either a problem with our scientific experiments, or there are other processes that cause a black carbon loss that we haven't found out about yet. Even a thousand year life span can't explain the carbon quantities.

Does the fact that we find charcoal in our ancient soils mean that this represents all the charcoal that was produced at that time? How do we know that we are not only finding a fraction of what was once there?

I would really like to believe that most the charcoal we put in our soils will stay there indefinately, but am struggling to do so until I find some peer reviewed evidence that proofs this.

Can anybody provide me with this?

Mariska


  
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