Sunday, May 13, 2007

Agrichar future

In a post earlier today: Mental Rut, Back40 takes Johannes Lehmann, soil scientist, and terra preta front man, to serious task for cheer leading the politically attractive aspects of TP:

Agrichar should not be crufted up with political baggage or tainted by association with the various climate hysteria inspired carbon wheezes. That it sequesters carbon in a more durable form than forests or other organic forms is a plus, but not its primary value. It is just one of the multiple benefits of agrichar. That fact should not be lost in a blaze of hype. It's the wrong message.
Back40's comments make good sense. Consider that terra preta has serious political problems in the offing. Charcoal production as a tool to combat global warming can be understandably counterintuitive. Char's mode of action in the soil is only partly understood, the degree of benefit to the soil is not well documented. Claimed char additions may be difficult to monitor.

Various blog and forum posts ask: Does the fuel value of charcoal provide a dangerous incentive to divert agrichar to fuel use? To overharvest biomass? Can the reality of terra preta nova be separated from marketing pitches by commercial pyrolysis interests?

In this environment, poor marketing choices will hurt the prospects of terra preta. We terra preta advocates need to distinguish our advocacy for improved soil from our advocacy of commercial pyrolysis and of char carbon sequestration. The value of char as a soil amendment can, and must, stand on its own merits. Only successful implementation of terra preta nova in stand alone and market driven settings can validate the fundamental benefits of biochar.

The agricultural value of charcoal is competing well with its fuel value at a market price of about $100/ton. Agrichar doesn't appear to need carbon sequestration subsidies, and at $4 a metric ton CO2, maybe it isn't even worth the paperwork.

Charcoal is fairly simple, and generally profitable to produce. The pyrolysis process used to produce char is adaptable and scalable. It can be used to co-generate heat, nitrogen fertilizer, hydrogen fuel and/or electrical power, indicating ample incentives to increase charcoal supply capacity. Rising fuel prices seem certain to increase the supply of charcoal.

The price of charcoal is driven mostly by its value as fuel. Coke, originally derived from coal to replace charcoal, cost about $100/ton in late 2006, which seems to also be about the same price as charcoal at the time. Significant quantities of charcoal are used in Japan for agriculture at these market prices.

Proponents of terra preta hope to speed adoption by subsidizing it with carbon credits. Currently CO2 sequestering goes for about $4 per metric ton on the carbon credit market. Carbon dioxide units at full molecular weight can be converted into carbon units by dividing by 44/12 (see endnotes here). Thus the carbon credit value of amending soil with charcoal is currently $14.67 per metric ton, or $13.31 per ton. This could be a nice kicker but the soil amendment value of charcoal, at $100/ton, is the significant component.

Note: Image from Flickr by carlosjwj (Location: Korogocho, Nairobe)


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