Biochar: Carbon Mitigation from the Ground Up

Was doing one of my weekly Scopus searches for new articles and came across the following review (PDF, 4 pages) on biochar, and it seems rather timely given that I've highlighted this topic recently. The title of this blog is taken from the title of the article, and it talks about the terra preta soils of the Amazon.

The soils are proof of concept that burying biochar (biomass-derived charcoal) in the soils will both: increase soil productivity/fertility; and trap carbon for long periods of time in the soil. Quoting the work of Christoph Steiner, one of the leading experts in the area of biochar, the article relates that: ... charcoal-mediated enhancement of soil caused a 280-400% increase in plant uptake of nitrogen, an element essential for crop production.

So how did the terra preta come about? There are competing theories:

Anna Roosevelt, a professor of anthropology at the University of Illinois at Chicago, believes terra preta was created accidentally through the accumulation of garbage. The dark soil, she says, is full of human cultural traces such as house foundations, hearths, cemeteries, food remains, and artifacts, along with charcoal. In contrast, Erickson says he’s sure the Amazonian peoples knew exactly what they were doing when they developed this rich soil. As evidence, he says, "All humans produce and toss out garbage, but the terra preta phenomenon is limited to a few world regions."

As I've mentioned before though, not all biochar is identical, and this article highlights some research pointing out this fact:

However, not all biochar performs the same. The importance of biochar’s variable chemical composition was illustrated in studies by Goro Uehara, a professor of soil science at the University of Hawaii, who grew plants both with and without biochar made from macadamia nutshells. He says, "As we added more [biochar], the plants got sicker and sicker." Uehara’s colleague, University of Hawaii extension specialist Jonathan Deenik, says that when they repeated the experiment with a more highly carbonized version of the nutshell biochar, which contained lower levels of volatile compounds, "preliminary results in a greenhouse study showed that low-volatility [biochar] supplemented with fertilizer outperformed fertilizer alone by 60%, in a statistically significant difference." This research was presented at the October 2008 annual meeting of the Soil Science Society of America.

From my particular vantage point, some biochars will act as a chelator (e.g., activated carbon) and pull essential nutrients (e.g., calcium, zinc, copper, iron) out of the soil, making them unavailable for plants and microbes.

However, in terms of storage capabilities, what does biochar bring to the table?

The calculations for potential carbon storage can be estimated downward from the amount of atmospheric carbon that photosynthesis removes from the air each year; using figures from the Intergovernmental Panel on Climate Change, Amonette estimates that number at 61.5 billion metric tons. He says the best estimates are presented in four scenarios for carbon storage calculated by the nonprofit International Biochar Initiative (IBI), a consortium of scientists and others who advocate for research/development and commercialization of biochar technology. The IBI’s "moderate" scenario assumed that 2.1% of the annual total photosynthesized carbon would be available for conversion to biochar containing 40% of the carbon in the original biomass, and that incorporating this charcoal in the soil would remove half a billion metric tons of carbon from the atmosphere annually. Because the heat and chemical energy released during pyrolysis could replace energy derived from fossil fuels, the IBI calculates the total benefit would be equivalent to removing about 1.2 billion metric tons of carbon from the atmosphere each year. That would offset 29% of today’s net rise in atmospheric carbon, which is estimated at 4.1 billion metric tons, according to the Energy Information Administration.

Pretty significant, eh?

An additional beauty to biochar is that it technically doesn't take a sophisticated setup to produce it:

Among other projects, the students made their own biochar in a 55-gallon drum and found that positioning the drum horizontally produced the best burn.

But biochar alone cannot solve our problems ... we need to better use our existing resources, and recycle!

As a carbon mitigation strategy, most biochar advocates believe biochar should be made only from plant waste, not from trees or plants grown on plantations. "The charcoal should not come from cutting down the rainforest and growing eucalyptus," says Amonette.

Now, all we need to do is get cracking and get into long-term field studies.

Reference
Tenenbaum, D.J. (2009). Biochar: Carbon mitigation from the ground up. Environmental Health Perspectives, 117 (2): A70-A73.