top of page

Biochar—Is It Time to Give 'Black Carbon' the Green Light?

Biochar, postproduction.  ©Oregon Dept of Forestry/Wikimedia  CC BY 2.0
Biochar, postproduction. ©Oregon Dept of Forestry/Wikimedia CC BY 2.0

From fabled lost cities to mysterious ancient artifacts, for centuries the Amazon has inspired imaginations with tales of adventure, discovery, and feats of great civilizations long gone.

But what if the real treasures to be found were not the gold of idols or the ornate designs of ceramic pots but knowledge of how to make soil more productive, resilient, and beneficial to the environment?

It was the indigenous peoples of this part of the world who first discovered and used something called biochar, and now those lessons from the past are inspiring the researchers of today.

Biochar’s promise is multifold. Not only can it improve soil quality and, therefore, food production, but by its very nature it actively reduces greenhouse emissions. For this reason, it is seen as something that could become a pillar of climate-smart agriculture.

But are some things best left in the past, or could biochar help inspire a new era of farming?

Biochar application in Namibia as part of the Bush Control and Biomass Utilization Project.  ©GIZ/Tim Brunauer/Wikimedia (CC By-SA 4.0)
Biochar application in Namibia as part of the Bush Control and Biomass Utilization Project. ©GIZ/Tim Brunauer/Wikimedia (CC By-SA 4.0)

What is Biochar?

Biochar gets its name from a combination of the Greek word bios—meaning life—and “char,” short for charcoal.

It is a type of charcoal made through “pyrolysis,” a process in which organic material from agricultural and forestry waste, like wood chips or old leaves (also known as biomass), are burned in containers with very little oxygen, which prevents combustion. This creates a highly porous and fine-grained charcoal with a high pH and carbon content, and has a much slower decomposition rate than the original biomass. This process also gives it its strikingly black appearance and the nickname “black carbon.”

Although it has seen a recent revival in interest, biochar is not new. It was first used more than 2,000 years ago in the Amazonian basin. People there created fertile and rich areas of soil called terra preta—which means “dark earth.”

Homemade TerraPreta (charcoal marked by white arrows).  ©Holger Casselmann/Wikimedia CC BY-SA 3.0
Homemade TerraPreta (charcoal marked by white arrows). ©Holger Casselmann/Wikimedia CC BY-SA 3.0

These scattered patches of black earth stood in sharp contrast to the acidic and nutrient-poor soil found in the rest of the rain forest. Biochar soil was higher in biomass and produced a greater proportion of edible foods.

Benefits of Biochar

To get maximum use from soil, it must retain its “good stuff”—its ability to retain water and nutrients—and that is where biochar comes in.

Biochar composition helps soil hold onto nutrients and water while increasing biodiversity and making it extra resilient to droughts. It is also lightweight and has a large surface area so it can be spread over larger areas of farmland.

The process also releases little, if any, contaminants, and the heat generated can be captured and used as clean energy.

Modern Research

Biochar has enjoyed a recent revival in interest, due to the growing need for new solutions to the world’s environmental and food-production problems.

Making biochar in a pit.  ©istock/ronemmons
Making biochar in a pit. ©istock/ronemmons

Indigenous peoples typically produced biochar by burning organic materials such as wood, crop residues, or animal manure in pits or mounds and then burying the resulting charcoal in the soil to improve fertility.

In contrast, modern methods typically involve using specialized equipment to pyrolyze organic materials at high temperatures in an oxygen-limited environment.

Using pyrolysis to make biochar. © Istock/Vector Mine
Using pyrolysis to make biochar. © Istock/Vector Mine

Dr. Wei Ren, associate professor at University of Connecticut’s Department of Natural Resources and the Environment, has been one of the academics involved in this new wave of biochar research.

Her team synthesized global data from nearly 600 studies on biochar to analyze its potential as a climate-smart agricultural practice.

The study highlighted the effects of biochar in field experiments on crop yield. The data showed that "biochar significantly increased gross soil organic carbon (SOC) stocks (by 26.6%) and crop yield (15.7%), reduced soil CH4 (−14.8%) and N2O (−23.1%) emissions, and ammonium (−24.9%) and total inorganic N leaching (−23.2%) but had no effect on soil CO2 emissions."

Dr. Ren told The Earth and I: “Many studies suggested that biochar applications could store carbon in the soil, boost crop yields and ability to withstand extreme weather events, increase fertilizer efficiency, dispose of non-hazardous waste from agriculture and forestry, and help increase climate resilience in farming systems.”

“When it comes to applications at broad scales, further efforts are still needed to investigate its techno-economic feasibility [and] stability in the soil.”

Dr. Ren added that given that a significant portion of total greenhouse gas emissions are attributed to the food systems, a successful biochar strategy could play an essential role in mitigating climate change and contributing to sustainable agriculture, but also cautioned that more research needed to be done.

She said: “When it comes to applications at broad scales, further efforts are still needed to investigate its techno-economic feasibility, stability in the soil, effects on soil properties and a wide range of ecosystem services and life cycle assessment.”

Potential Drawbacks

Some studies have reported adverse effects of biochar, suggesting it may increase the pH of acidic soils and suppress some crop yields, due to reduced nutrient and water availability.

Dr. Ren said that environmental and societal benefits of biochar applications are “highly variable” and “large uncertainties” remain.

She added: “Biochar effects highly depend on natural and anthropogenic factors, such as soil and climate conditions, management practices, crop types, biochar types, etc. It needs further effort to examine biochar’s environmental benefits and the trade-off between benefits and cost.

“Our studies suggest that the effectiveness of biochar applications highly depends on soil and climate conditions and their combination with other conventional or conservation practices. However, it needs further efforts to identify if particular parts of the world especially benefit from biochar applications.”

The team’s work has drawn the attention of the research community and the public, including biochar companies and other organizations that have contacted Dr. Ren with interest in collaborations.

Dr. Ren said her research will continue focusing on interactions among climate, ecosystem, and human activities.

Black Carbon or Black Gold?

The lost treasures of antiquity are usually depicted as gold goblets and fine stone works, but the potential bounty of lost and revived knowledge could perhaps prove even more precious.

Biochar could be one such benefit, helping to enable soil to preserve its richness while also helping to cut the impact of greenhouse gas emissions. But it is clear more work needs to be done to establish whether it can be put into widespread use.


*Mark Smith is a journalist and author from the UK. He has written on subjects ranging from business and technology to world affairs, history, and popular culture for the Guardian, BBC, Telegraph, and magazines in the United States, Europe, and Southeast Asia.


Join Our Community

Sign up for our bi-monthly environmental publication and get notified when new issues of The Earth & I  are released!


bottom of page