Muck and Mystery
   Loitering With Intent
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March 24, 2009
New Moon

Consider the source.

Biomass is suddenly the universal answer to our climate and energy problems. Its advocates claim that it will become the primary source of the world’s heating fuel, electricity, road transport fuel (cellulosic ethanol) and aviation fuel (bio-kerosene). Few people stop to wonder how the planet can accommodate these demands and still produce food and preserve wild places. Now an even crazier use of woodchips is being promoted everywhere (including in the Guardian(1)). The great green miracle works like this: we turn the planet’s surface into charcoal.

Sorry, not charcoal. We don’t call it that any more. Now we say biochar. The idea is that wood and crop wastes are cooked to release the volatile components (which can be used as fuel), then the residue - the charcoal - is buried in the soil. According to the magical thinkers who promote it, the new miracle stops climate breakdown, replaces gas and petroleum, improves the fertility of the soil, reduces deforestation, cuts labour, creates employment, prevents respiratory disease and ensures that when you drop your toast it always lands butter side up. . .

Peter Read says that the new plantations can be created across “land on which the occupants are not engaged in economic activity”(13). This means land used by subsistence farmers, pastoralists, hunters and gatherers and anyone else who isn’t producing commodities for the mass market: poorly-defended people whose rights and title can be disregarded. Both Read and Carbonscape speak of these places as “degraded lands”. We used to call them unimproved, or marginal. Degraded land is the new code for natural habitat someone wants to destroy. . .

As Almuth Ernsting and Rachel Smolker of Biofuelwatch point out, many of the claims made for biochar don’t stand up(17). In some cases charcoal in the soil improves plant growth; in others it suppresses it. Just burying carbon bears little relationship to the complex farming techniques of the Amazon Indians who created terras pretas. Nor is there any guarantee that most of the buried carbon will stay in the soil. In some cases charcoal stimulates bacterial growth, causing carbon emissions from soils to rise. As for reducing deforestation, a stove that burns only part of the fuel is likely to increase, not decrease, demand for wood. There are plenty of other ways of eliminating household smoke which don’t involve turning the world’s forests to cinders.

None of this is to suggest that the idea has no virtues; simply that they are outweighed by hazards, which the promoters have either overlooked or obscured. Nor does this mean that charcoal can’t be made on a small scale, from straw or brashings or sewage that would otherwise go to waste. But the idea that biochar is a universal solution which can be safely deployed on a vast scale is as misguided as Mao Zedong’s Great Leap Backwards. We clutch at straws (and other biomass) in our desperation to believe that there is an easy way out.

As I've been predicting for a few years, over-hyping biochar results in a backlash. The backlash is just as mistaken as the over-hyping. The media circus - pro and con - is a distraction.

Using char for agricultural purposes is one part of an agronomic system that still has to do all of the other parts of the system in appropriate ways. When understood this way and used insightfully the system is improved.

One value of the media circus about char might be as a stimulus for conversation. Is it true that "In some cases charcoal in the soil improves plant growth; in others it suppresses it"? If so, why? Are there any comparably analogous situations?

Yes, the same is true of manure, and the explanation for why this is so parallels the char effect. When chemically and biologically active material is cannon-balled into the soil there's a period of adjustment required. Manure is organic and so not useful for plants, which require mineral nutrients. Soil organisms can convert the organic nutrients to mineral nutrients, but that takes time and during the process the soil goes into nutrient deficit as the organisms consume some of the existing nutrients in the soil in order to convert the manure. In the end the soil is improved. One has to consider the whole system over time to understand the true effect of manuring.

Char absorbs water and some nutrients, holding them for later release. The initial effect of putting raw char in the soil can be a deficit something like the initial manure effect. To counter this char can be "pre-loaded" with water and nutrients, or balanced by simultaneous addition of other soil amendments. In the end, soil is improved just as with manure, but in a different and more durable way. It doesn't replace manure, it enhances the effect. Using them together is a best practice.

There's a similar explanation of the charge that "charcoal stimulates bacterial growth, causing carbon emissions from soils to rise". This is true at first, but over time carbon emissions are reduced and the net benefit is positive. Soil carbon in both organic and inorganic forms increases due in part to the stimulation of soil bacteria and fungi.

The political and media circus will proceed in its foolish inevitable way as opportunists jockey for power and profits. It's a shame that this is so, but it is so.


Another way to understand the effects of soil amendment using char is to compare it to liming. Adding lime, calcium carbonate, to soil reduces soil acidity as well as providing calcium - a necessary secondary nutrient that is critical to soil and plant health. Not all soil is acidic, so it isn't always the right thing to do, or it must be balanced by other materials, such as sulfur, to buffer the PH change for a net zero PH effect while still providing calcium. Using gypsum, calcium sulfate, does the trick.

The effect of liming acidic soil isn't immediate. Some months pass before it fully kicks in and then has diminishing effects over a period of years depending on how finely ground the material is when added. The finer it is ground the quicker, stronger but less lasting the effects.

Wood ash is another sort of amendment that is loosely comparable to char and lime. It raises PH so is useful on acidic soil, and contains soil nutrients such as calcium, potassium and phosphorous. The full effect takes time as the chemical and biological changes settle in, and can seem counter-productive at first. The grower has to be able to anticipate the timing and effects.

It hardly seems sensible to complain that farming takes knowledge and skill to do well, but that is what char critics are doing. They get away with it to some extent because their audience is ignorant too. Politicians, journalists and the general non-farming public can be easily duped. What goes around comes around. Over-hyping char to an ignorant public provided a platform for critics to stand on and bloviate.

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