Photo: Dark earth could herald a bright future for agriculture and climate

(Credit: Eden Graham via Flickr)

By David Suzuki with contributions from David Suzuki Foundation Senior Editor Ian Hanington.

Feeding more than seven billion people with minimal environmental and climate impacts is no small feat. That parts of the world are plagued by obesity while starvation is rampant elsewhere shows part of the problem revolves around distribution and social equity. But agricultural methods pose some of the biggest challenges.

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Over the past half century, the world has moved increasingly to industrial agriculture — attempting to maximize efficiency through massive, often inhumane livestock operations; turning huge swaths of land over to monocrops requiring liberal use of fertilizers, pesticides and genetic modification; and reliance on fossil fuel-consuming machinery and underpaid migrant workers. This has contributed to increased greenhouse gas emissions; loss of forests and wetlands that prevent climate change by storing carbon; pollution from runoff and pesticides; antibiotic and pesticide resistance; reduced biodiversity; and soil degradation, erosion and loss.

The "solution" offered by many experts is to double down on industrial agriculture and genetic modification. But doing so ignores how natural systems function and interact and assumes we can do better. History shows such hubris often leads to unexpected negative results. Others are attempting to understand how to work within nature's systems, using agroecological methods.

One promising development is the renewed interest in a soil-building method from the distant past called "dark earth" or "terra preta," which involves mixing biochar with organic materials to create humus-rich soil that stores large amounts of carbon. In the book Terra Preta: How the World's Most Fertile Soil Can Help Reverse Climate Change and Reduce World Hunger, Ute Scheub and co-authors claim increasing the humus content of soils worldwide by 10 per cent within the next 50 years could reduce atmospheric CO2 concentrations to pre-industrial levels.

Dark earth's benefit to climate is just one of its many exciting possibilities. It also enhances soils so they produce higher yields, helps retain water and prevents erosion. It's more alive with biodiverse micro-organisms, making it easier for crops to adapt to changing conditions. And it's a good way to recycle nutrient-rich food scraps, plants wastes and even human and animal urine and feces, rather than allowing them to pollute soil, water and air through burning and runoff.

Biochar is a form of charcoal made via pyrolysis — heating organic wastes in a low-oxygen environment. According to Scheub, "If you pyrolyze organic wastes, up to 50 percent of the carbon, which plants have extracted from the atmosphere in the form of carbon dioxide, is converted into highly stable carbon, which can persist in soils for thousands of years." As well as carbon, biochar retains nutrients like nitrogen and phosphorous, and because it's porous, adding it to soils and compost helps them store nutrients and water.

Western scientists first studied terra preta in 1874 when Canadian-born Cornell University professor Charles Hartt and his team found patches of dark, fertile soils, several metres deep, along parts of South America's Amazon River where earth is normally low in nutrients and organic matter. Later archeological research determined the soils were created by human communities up to 5,000 years ago.

Scientists have since shed more light on the technique. Because the ancient practice is still employed in Liberia and Ghana, Africa, scientists from Sussex, Cornell and other universities were recently able to compare dark earth to soils nearby where the technique isn't used. They found dark earth contained 200 to 300 per cent more organic carbon and can support "far more intensive farming."

Cornell University lead author Dawit Solomon was surprised that "isolated indigenous communities living far apart in distance and time" achieved similar results unknown to modern agriculturalists. "This valuable strategy to improve soil fertility while also contributing to climate-change mitigation and adaptation in Africa could become an important component of the global climate-smart agricultural management strategy to achieve food security," he said.

Scheub and her co-authors say the technique can be used on any scale, from home and community gardens to large farms. Terra Preta includes instructions for creating biochar and enhanced soils, but cautions that organic wastes should be used rather than valuable forest products.

Dark earth won't solve all our climate problems, but combined with reducing fossil fuel use, it could make a huge difference while addressing many agriculture, food security and hunger issues.

July 7, 2016

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Jul 21, 2016
7:25 AM

Maybe not such a great idea. Successful dark earth happened over a very long time using waste (from cooking fires, etc). Using new materials to make biochar is not the way to go, unless you’re looking for an opportunity to make money.

Jul 13, 2016
9:55 AM

This shows that we are just beginning to catch up to Indigenous science — if we really listen.

Jul 11, 2016
8:46 AM

Our farm received a grant from the USDA’s Natural Resources Conservation Service to develop a methodology for sustainable (i.e. feasible and affordable!) on-farm small scale biochar production. The full report — including plans for the pyrolysis unit — and other information is available at:

PS I grew up in Biggar, SK and spent tons of time in BC as a kid visiting relatives in Vancouver

Jul 11, 2016
8:32 AM

I haven’t read Terra Preta yet but a friend of mine, who many years ago headed composting science at Agriculture Canada wrote:

“…I recall dealing with this issue in a departmental note about 28 years ago..If I recollect correctly, I opined that biochar made sense where there were no domesticated animals such as in native American cultures and some in Africa . There the wastes available were mainly carbonaceous Where both carbon-rich crop and fixed nitrogen-rich animal wastes were available it made sense to compost the two. The compost conserved and provided nutrients to crop plants in biological synchrony with their growth, and humus that I used to say was the soul of soil. It sheltered the essential soil biota and buffered, optimized, the biological, physical and chemical attributes of soil. Relatively biochar is inert and simply coal that burns every time there is fire on the land, releasing CO2, But it is definitely better than applying the carbon-rich and nitrogen-poor crop waste alone into soil as that would cause nitrogen starvation for crop plants as the decomposer organisms have first call on whatever nitrogen is available…

I therefore feel that composting would be better for modern cultures…”

Jul 09, 2016
8:59 PM

I posted this on your facebook page and putting it here as I think it’s important to balance out the information in the article above.

What about the not so ecological aspect of biochar? BioChar is a very cool marketing term using half truths to sell it. It’s just charcoal and people should have a massive problem with it. I liken it to synthetic fertilisers. Yes it works but it’s certainly not ecologically sound to be burning all the amazing nutrient locked up in the wood and then burying the hollow skeletal remains into the earth so that when nutrient does enter the soil it can hopefully then re-insert itself back into the wood skeleton.

I’d have no problem if it was a waste product/byproduct of something, then it has a small environmental impact. Unfortunately it’s creating an industry of people burning perfectly good organic wood to create biochar as well as backyard burning with no reticulation systems to catch the released gasses. I looked into it and even some of the biggest advocates of it contradict themselves. Stating it locks up compounds and gasses in the soil that are bad for the environment yet a simple search reveals those same gasses and more toxins are released into the atmosphere during the creation/ burning process of the charcoal.

Why not let that same wood break down naturally in the earth and create amazing organic soil aka mulching/ hugelkulture, just like nature intended? Impatience and money to be made is the answer. Those tribes weren’t burning down the Amazon rainforest to make soil. Those “terra petra” pits are a byproduct of their use of fire to cook and keep warm.

So yes bury the leftover coals/ash from your barbecue/fireplace (which I myself do) but don’t for one second think BioChar is anything more than overpriced charcoal and a marketing gimmick.

Jul 09, 2016
3:43 PM

Very well, very nice, but a bit tricky to achieve. One way is to use a small furnace called neostove which uses wood granules, or even other kind of small wood matter. The burning goes in two moments. It starts with the «flame» moment called pyrolise. Nice clean burning. Then it burns the coal,, and that’s where you stop the burning process to grab that coal, Flush it into any can of water to stop the burning, From then, simply crush those coals into the finest dust, You’ve got biochar.

That’s one way around the problem, The other way is to get the wood to decay by the mushroom. Simply lay your wood matter on the ground (ground with earth, not asphalt or concrete) and leave it to turn into basically the same stuff as biochar: carbon matter with living organism living in. For best results, use alife winter hard wood branches reduced to the size of coins and lay it no more than 10cm thick.

Jul 08, 2016
4:27 PM

This article fails to mention one singular and necessary fact. It doesn’t say how biochar helps in reducing climate change. Biochar burial is carbon dioxide negative, a carbon sink, in that is it stores carbon taken from the atmosphere by plants. Otherwise why would the subject of climate change even be in the article?

Jul 08, 2016
1:18 PM

Amending topsoil with compost derived from yard and municipal green bin organics recycling programs as a standard practice in the construction or renovation of landscaped portions of our communites would produce urban environments that are more fertile (i.e., easier to establish and maintain tree and vegetation cover), produce less runoff during wet weather, and have a higher tolerance to drought conditions that are anticipated in a changing climate.

Research by the Sustainable Technologies Evaluation Program (STEP) is underway to evaluate the effects of compost amended topsoil on runoff and interflow properties of lawns receiving roof drainage at The Living City Campus at Kortright, in Vaughan, Ontario. (

Dean Young Project Manager, Sustainable Technologies Toronto and Region Conservation

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