On Nov 18, 2011, at 11:31 AM, John D'hondt wrote:
I am well aware of the stability of charcoal but that it serves as living
space for microbes is pure nonsense. You can't have it both ways. If it were
good for microbes it would not be stable. It is one or the other and you
really can't keep your cabbage and eat it at the same time.
Well, you don't eat your house, either, even though it's made of carbon just as your cabbage is. They are different substances, with different functions, just as biochar and humus are.
And I also can't see it as a sink for soil minerals. As a slow sink for
mercury yes and organic pesticide molecules probably.
Yes, it is a sink for soil minerals. See, for example, "Black Carbon Increases Cation Exchange Capacity in Soils" from the Soil Science of America Journal. Abstract is at
http://www.biochar-international.org/node/157 though the article needs a subscription to view.
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.
I hope not to hear the claim that biochar can't house microbes or donate nutrients any more. These are very well proven facts and have a very solid mechanism behind them.
I don't see biochar as a silver bullet. Like everything else, if made on an industrial scale, it be just as poor a product, and just as damaging, as industrial organic food or industrial medicine. But that is the fault of industrialization, not biochar.
Toby
http://patternliteracy.com
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