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FALL 2010
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Feature: Food and Energy Systems

Biochar: An Ancient Solution for a Modern Problem

Secrets of the dark, fertile Amazonian soils reveal ways to sequester carbon and slow climate change.
By E. Lauren Chambliss


Deep in the heart of the Amazon rain forest in Brazil is a centuries-old substance of mysterious origin that some scientists believe could play a leading role in saving the planet.

Johannes Lehmann
University Photography

Johannes Lehmann holds biochar, left, and the biomass from which it was created

Known variously as “black gold,” “Terra Preta de Indios,” or “dark earth,” it is a particular type of fertile Amazonian soil. Its claim to fame is biochar, the charcoal-like substance that is in it. Biochar is igniting the interest and passion of scientists around the globe, including those at the White House.

“Biochar is capturing attention because it offers opportunities for discovery at the frontiers of science,” says CALS soil scientist Johannes Lehmann, one of the world’s leading terra preta experts and co-founder of the International Biochar Initiative (IBI). “In the past five years there has been an explosion of interest from politicians, NGOs [non-governmental organizations], the business sector, and the scientific community.”

By way of example, at the first IBI international conference five years ago, about 100 people attended and 40 papers were presented. At the last annual meeting this past September in Rio de Janeiro, about 500 people attended and 100 researchers from around the globe presented their findings.

So what’s all the fuss about biochar? This highly porous, dark-chocolate-looking substance with a granular feel is considered by many scientists to be a potential “black gold” for agriculture. What a Swiss army knife is to a penknife, biochar is to regular charcoal—a multipurpose tool with numerous applications for agriculture, bioenergy, waste disposal, and atmospheric detox.

First, it’s a great way to get rid of agricultural waste. Biochar can be made from crop residue, wood chips, cow manure, and other biomass, as long as it is cooked at low heat in the absence of oxygen, a process called pyrolysis. Second, in the conversion process, energy is produced in the form of syngas, which can be converted to heat and power. Third, after the syngas has been driven off and converted to energy, carbon-rich biochar remains, which, when returned to the earth, helps soil retain water and nutrients and, ultimately, increases crop yields, especially in poorer-quality soils. Lastly, biochar is a natural carbon sink—sequestering CO2 and locking it into the ground, for hundreds of years.

“With biochar you have multiple sustainability outcomes—waste management, energy produced, soils improved, and carbon sequestered,” says Lehmann, associate professor in the Department of Crop and Soil Sciences. “This is what has people so excited.”

And here’s where saving the planet comes in: From a carbon sequestration standpoint, think of biochar as a two-way filter. It helps clean the air by preventing rotting biomass (for example, crop residue or wood refuse from harvested forests) from releasing CO2 into the atmosphere by converting it into biochar instead. When it is added back into the soil, it locks in carbon in a stable form and helps plants to thrive, storing additional CO2 they pull out of the air during photosynthesis.

Terra Preta

Layers of terra preta are clearly evident in this section of Amazonian soil.

Collecting Samples

Collecting biochar samples in the field.

Biomass to Biochar

In fact, Lehmann’s latest research collaboration shows that biochar could help slow the increase in total human-caused greenhouse gas emissions (GHG) believed to be the leading culprit behind global climate change, according to the Intergovernmental Panel on Climate Change (IPCC) and the vast majority of leading scientists, including those at Cornell.

Detailed in the August 10 issue of Nature Communications, Lehmann’s research posits that the use of biochar has the potential to mitigate climate change on a much larger scale than combustion of the same sustainably procured biomass used for energy output alone. In other words, if you took all of the available sustainably harvestable biomass (which means not taking food crops out of rotation or clearing land for new crops) and used it to replace fossil fuel, that would still not be as beneficial from a GHG emissions reduction standpoint as using the biomass to create a mixed energy/biochar stream.

If biomass that could be collected sustainably were converted to biochar and the gas produced in the conversion process were used for energy, human-caused greenhouse gas emissions could be reduced by one gigaton—or up to 12 percent—annually, according to the new research.

Lehmann’s collaborators, lead authors Dominic Woolf of Swansea (UK) University and James E. Amonette of the Pacific Northwest National Laboratory in Richland, Washington, looked only at the world’s supply of crop leftovers, such things as corn leaves and stalks, rice husks, livestock manure, yard trimmings, and crops grown on marginal lands. Such a shift in biomass use is not practically feasible, and would require enormous policy and infrastructure changes. In addition, pyrolysis technology is not yet advanced enough to be built at the commercial scale necessary for mass energy/biochar production.

Private investors and energy companies are just beginning to invest in breakthrough technology. Lehmann himself is in the process of securing a research-scale unit that would be the first of its kind in the Northeast, giving Cornell the first biochar-producing pyrolysis technology north of the Mason-Dixon line and one of only a handful of such research units in the United States.

But the study was not trying to measure the practical application of pyrolysis. The research was designed to show whether or not pyrolysis and biochar as an energy/GHG mitigation system is worth pursuing as part of a viable solution to the global climate crisis. And that, the study clearly showed, is a giant “yes.”

“What we wanted to know is how much biochar can contribute in a sustainable way and is that number high enough to justify pursuing this technology,” Lehmann says. “There are a lot of challenges—technical, economic, and political—that are not probed here. But it is exciting to see what is possible with biochar.”

Findings like these have publications as diverse as Rolling Stone, National Geographic, Time Magazine, and the American Society of Agronomy touting biochar’s benefits. In Washington, D.C., biochar is creating buzz, as well. Lehmann was recently asked to brief the President’s Council of Advisors on Science and Technology, and Senator Harry Reid (D-Nevada) has introduced a bill in Congress to support further exploration.

Indigenous Groundwork

The next steps are clear. According to Lehmann, many detailed pieces of information have to be gathered. But the most important goal is to “test biochar at work” on a farm or in a community to really know whether it can deliver.

Still, there remain a lot of unanswered questions about the mysterious matter, including how it got into the Amazon soil in the first place.

Pockets of “terra preta” have existed for centuries along the banks of the mighty Amazon, where indigenous populations thrived for centuries until Spanish and Portuguese explorers arrived in the mid-1600s with infectious diseases against which native populations had no immunity.

The tribes that once lived there were efficient farmers who grew cassava and corn, among other things, in soil made rich with smoldered plant matter. Whether they did so by design—purposefully creating biochar by burning crop refuse in underground (oxygen-less) pits and adding it to soil—or it ended up there as a byproduct of the way they lived, is a question scientists debate today. Lehmann is one of the growing number who believe these early Amazonian growers knew what they were doing. Farmers through the ages have utilized “slash-and-burn” on fields as a way to improve crop performance, but Lehmann is convinced these indigenous farmers went one better and found a way to create a particularly rich and long-lasting carbon-rich form, today’s biochar.


Researchers work in the Amazon where biochar laid down centuries ago enriches the earth.

“I first became interested in biochar 12 or 13 years ago when working in the Central Amazon,” he says. “You can’t help but notice the fertility difference in the landscape between the terra preta soils and the surrounding areas. When you dig deeper you see these soils are built on chars laid down a few hundred to several thousand years ago and they have maintained their fertility over the centuries.”

It is only in the last few years that biogeochemistry has begun to unlock the secrets of the soil, and show how biochar differs markedly from other soil organic matter and why it is especially valuable for soil fertility and carbon capture.

Biochar is even more loaded with carbon—about 80 percent or more can be pure carbon—than regular humus, and it has an incredible sponge-like surface, which traps nutrients and waters and creates a veritable “playground” for beneficial microbes that aid plant growth, according to Lehmann. It is a much more stable, meaning enduring, fertility-enhancing substance than, say, rotting plant stems, manure, compost, or other forms of uncharred biomass often added to soil to improve it.

The phrase “ancient wisdom” takes on new meaning as one of our newest hopes for saving the planet comes from one of the earth’s oldest agricultural practices.