permaculture

[Dieter Brand <diebrand@yahoo.com>]

Toby,

If we accept the view that plants only feed by receiving free ions, then what 
you say makes sense, but in that case there is no point of going to all the 
trouble of maintaining a soil biology; in fact, we might as well feed the 
plants directly with water-soluble fertilizers.  Nevertheless, I think even 
mainstream soil scientists do not deny that plants can also absorb 
macromolecules or even entire proteins or bacteria.  If we understand that, 
maintaining soil biology becomes tremendously important and organic farming 
becomes an urgent necessity.

To define humus as a medium for maintaining CEC is the reductionist view of 
the chemist.  Humus does much more.  Firstly it breaks down OM.  Why would 
the microbes that specialize in breaking down OM need to live in charcoal 
apartment buildings?  To live and work in different places is an idea of homo 
sapiens – and a fairly recent one at that.  The breaking-down microbes need 
to live and work in the OM.

Next, why would the microbes that got fat on the OM have to hide in those 
charcoal apartment buildings?  They are not supposed to hide anywhere; on the 
contrary, they are supposed to be eaten by protozoa, nematodes and other 
predators that produce the substances necessary for plant growth.

And finally, why should the microbes and fungi that colonize the plant roots 
to feed the plants want to live in the charcoal apartment buildings?  That is 
not where they are supposed to be.  They are supposed to colonize the plant 
roots, or else they cannot feed the plants.

So what type of microbes needs to live in those charcoal apartment buildings 
at what stage of decomposition, transformation or plant growth and for what 
purpose?  Each soil organism has a precise place and time of action.  Once 
that action has been accomplished they make way for something else.  Simply 
to say there are more microbes is not significant.

Microbes like all other soil organisms are part of humus.  They are not 
separate from humus.  They become humus when they die and humus becomes 
microbes when it is eaten by microbes.  At one time the soil is teeming with 
some types of microbes and at another time there are hardly any at all 
because there is nothing for them to do.  Then a certain type of microbe 
suddenly proliferates as a result of some work needing to be done: 
decomposing OM, hunting bacteria, feeding plants in spring, etc. I can’t see 
what the precise function of charcoal is in all of this activity.

Humus, like life, is a dynamic process and not a static substance.  In the 
cycle of life, the idea of a stable substance has no place or function – 
there is only change.

Dieter


--- On Fri, 11/18/11, Toby Hemenway <toby@patternliteracy.com> wrote:
> First, here's why biochar can house microbes and not break
> down. Microbes colonize surfaces. They do not always eat the
> surfaces they colonize. When they colonize gravel in reed
> beds, they don't eat the gravel. (Cred here: I  ran a
> microbiology lab at a large biotech company. We used to
> colonize inert surfaces with microbes all the time, like
> porcelain and carbon fiber. They didn't eat it.) 
> 
> I'm seeing a fundamental confusion between the roles of
> humus and biochar here that I hope to clear up. Humus feeds
> plants and microbes in two different ways, while biochar
> feeds them in only one way.  They both house microbes.
> The first way humus feeds is by its ability to hold cations:
> positively charged nutrient ions such as calcium, iron, etc.
> These cations are not part of the humus; they are
> hydrogen-bonded to the oxygen atoms on the humus. The
> cations are donated to the plant or microbe, and are
> recharged (returned) to the humus by the breakdown of other
> organic matter. When organisms eat cations, the humus
> remains unchanged.
> 
> The other way microbes (not plants) are fed by humus is
> when the microbes break down the humus itself, extracting
> energy and carbon from the humus. This results in
> degradation and loss of humus. New humus must be formed by a
> constant supply of new organic matter. Humus is always
> breaking down in this way, sometimes slowly if there is
> ample OM or few microbes, but fast if there is a lack of OM.
> That's part of why OM must be constantly added to soil.
> Biochar lasts far longer than humus in soil where there is
> microbial feeding. Humus is not as good a carbon sink as
> biochar.
> 
> Next,  biochar holds minerals in two ways. They can be
> directly adsorbed onto the surface, and since it has so much
> surface, it can hold a lot of minerals.. Also, although the
> carbon in it is positively charged, and thus won't bond to
> other +-charged cations, it raises CEC by adsorbing
> negatively charged substances in the soil, which then bond
> to cation nutrients. This is documented. It then releases
> the bound nutrients to microbes and plants the way humus
> does--and thus doesn't break down, just as humus does not in
> these cases. It also houses microbes but does not itself
> feed them carbon; the carbon has been largely stripped of
> the type of bond needed to fuel microbes. Charcoal alone
> will not feed microbes or plants. There must be other OM
> present. This is why I am puzzled by this argument. Charcoal
> and OM work together, it is not a case of one or the other.
> Biochar provides a long-lasting carbon storage, unlike
> humus. And OM provides the food.