Like me, you’ve probably heard that it takes thousands of years to create topsoil and replenish what is being eroded from farmlands. Evidently that’s not so. As I wrote in an earlier blog entry (see the archive at the right, where it is the first entry in March 2007). The Amazon farmers figured out how to produce rich black loam some 4,000 years ago – and it is still there in Brazil, replenishing itself within twenty years when it is removed. It's called “terra preta.” (See photo.) The deposits can be up to 1 –2 meters deep, though the average is around 40-50 cm.
Best yet, this rich soil is a wonderful carbon sink. Johannes Lehmann, a soil biochemist at Cornell University cites several other researchers, saying that,
“Soil organic carbon is an important pool of carbon in the global biogeochemical cycle. The total amount of organic carbon in soils is estimated to be 2011 Gt. C, which constitutes about 82% of the global organic carbon in terrestrial ecoysytems. Amazonian dark earths have high carbon contents of up to 150 g. C/kg soil in comparison to the surrounding soils with 20-30 g C/kg soil. ...Furthermore, the organic matter in the ark earths is persistent since we find these elevated carbon contents even hundreds of years after they were abandoned.”
These soils are highly fertile. Fallows can be as short as six months. Some terra preta lands have been under continuous cultivation without fertilization for over 40 years.
Clearly, if terra preta can be produced by or for farmers around the world, the prospects for agriculture are enhanced at the same time that the planet’s carbon sinks are greatly expanded.
But how can this be done? The magic secret of terra preta seems to be the burying of bio-char in the soil. Presumably any kind of organic waste could be converted to charcoal, but the main source is certainly wood. Charcoal is created by being burned slowly in the near-absence of oxygen, as for example by being buried throughout the burn cycle. This is a simple method.
Naturally, it would defeat our purpose if we cut down forests just to obtain the wood for the production of bio-char. Tragically, however, the Mountain Pine Beetle is destroying forests for us, It’s impossible to feel grateful for this devastation, which results from global warming. Cold winter weather used to kill the insects, but no longer does so, leaving them to kill wide swaths of forest in British Columbia and Alberta. In fact, the logging companies are working as hard as possible to remove dead trees before the wood becomes unusable. There are more wood products now, therefore, than can be used. Whole mountain ranges are covered with pines that are now red. A drive through the Rockies will shock you.
Though this destruction is tragic, there is a potential up-side, allowing us to replenish and enrich farm soil around the world, while sequestering large amounts of carbon for thousands of years. I hope some technical specialists will explore the following idea. (I am not a scientist, so I may be wrong, but it seems worth a look.)
What would work would be the creation of large furnaces near the dead forests. Loggers could bring the wood and other forest debris to the furnaces, where it would be burned in the absence of oxygen, thus producing bio-char. The resulting heat should not be wasted, but could be used to generate electric power (or conceivably for some other project requiring energy). Then the charcoal could be sold in North America or provided as development aid to poor farmers abroad, reducing the need for fertilizers, which can pollute.
If any readers have the right institutional contacts and can bring this possibility to their attention, I’ll be grateful.