Black Is the New Black: The Rise of the Terra Preta Underground

After the failure of world leaders to produce a climate protection plan in Copenhagen, burnt offerings and negative thinking can keep us positive.

The burnt offering is a breakthrough that can buy time by getting carbon dioxide from rotting plants out of the air and into the ground.

Move over carbon-neutral – yesterday’s watchword, and enter carbon-negative biochar, the great black hope. The char-broiled revolution is warming the hearts of scientists and entrepreneurs from the US, Germany, Brazil, Italy and Japan with the prospect that significant amounts of carbon from plants can be locked up in the soil to serve as a soil conditioner, instead of being released as global warming carbon dioxide.

Markham, Ontario technologist Lloyd Helferty, says that burying charred wood scraps and crop wastes in the ground – it’s the burial that makes the charred material biochar instead of charcoal – is a form of “reverse mining; we’re mining carbon from the atmosphere and putting it in the earth.” Burial not only keeps excess carbon away from the atmosphere, where it can cause huge problems of global warming; it locks the carbon in the soil, where it does a world of good for fast-growing plants that feed people while sucking down even more carbon – a win-win proposition for the environment and food production.

Over the last two decades, biochar – using charcoal as a soil conditioner and fertility-enhancer instead of as a fuel for the home barbeque or stove – has intrigued a group of biologists, soil scientists and archeologists fascinated by the soil building practices of the first human inhabitants of the Amazon.

The Amazon is usually depicted as a tropical forest built on barren land, while its Indigenous peoples are portrayed as hunters and gatherers. But in 1879, explorer Herbert Smith reported seeing stalks of sugar cane as thick as a man’s wrist growing out of deep, dark loam, referred to in Portuguese as terra preta, black earth. As far as anyone knows, the fertile loam was produced thousands of years earlier by Amazonians who understood what modern scientists didn’t start to figure out until the 1990s.

Early figuring was done by Wim Sombroeck, who was ten years old during the Dutch famine of 1944, when his family survived on food from an exceptionally fertile backyard strewn with ash and cinders from the fireplace. When he saw terra preta on a trip to the Amazon in the 1950s, according to Emma Marris’ lively report in Nature in 2006, Sombroeck recognized the magic of his childhood and devoted  his scientific career to studying it. In 1992, he developed the theory that terra preta techniques could store 250 tonnes of carbon per hectare in a safe place underground while serving as the building block for fertile farms.

Sombroeck also worked with the young Johannes Lehmann, now a distinguished crop scientist at Cornell University and global expert in what he calls biochar and “the biochar revolution.” It puts “bio-energy in the black,” he claims in a 2007 study in Frontiers in Ecology, where he advanced the argument that the complete biochar cycle could reduce carbon emissions from today’s reliance on fossil fuels while storing the atmospheric carbon from yesterday’s fossil fuels.

Here’s how the cycle works, as outlined in a score of Lehmann’s and his co-workers’ studies in a wide range of leading scientific journals since then.

Waste from logging (sawdust, twigs and bark) or crops (straw, manure, cornstalks, nutshells for example) are baked at low temperatures with minimal access to oxygen – a process sometimes called smoldering but more accurately called “pyrolysis.” The slow bake produces off-gases, which can be trapped and converted to bio-fuels that substitute for fossil fuels; about half is left over as char. So far, so carbon-neutral good; part of the carbon drawn from the atmosphere is returned to the atmosphere as smoke, while part produces fuel.

Then the carbon strut begins. Carbon is very stable. It can remain intact for as long as 9000 years, locking in the carbon drawn down by plants. That’s a lifeline in terms of slowing down the pace of the carbon cycle, since plants absorb carbon dioxide as they grow and then give it back as they rot or burn – the way things worked to keep everything in balance until the burning of coal, oil and gas spewed off carbon that had been locked underground over millions of years.

Stable carbon is good, but the nooks and crannies in char are even better. They provide surface area for what’s called cation exchange capacity — CEC, in case you’re at a cocktail party with soil nerds. All these openings give biochar a huge surface area to bind to both water and other soil elements and keep them in place, as well as hiding places for bacteria that break down nutrients in the soil. The combination of surface area and bacteria means that char breaks down nutrients and makes them readily available to plants.

Likewise, the nooks and crannies store water and keep key fertilizers such as nitrogen and phosphorous in the topsoil, where they feed plants, rather than letting them drip down to the water table, where they pollute lakes and rivers. As a result of biochar, food crops bloom on newly fertile land – yields shoot up from 60 to 189 per cent in different sites Lehmann studied — while lakes and rivers remain stocked with fish. Less fertilizer, usually made with fossil fuels, is needed, and bigger plants suck down more carbon – a virtuous circle for humans and the environment.

Lehmann estimates this charbroiled carbon cycle could remove “a few billion tonnes a year” of carbon from the air, a nice piece of the climate protection action.

Less carbon in the sky is not pie in the sky.  Leading science policy advisers, including the European Union’s Frank Raes, support active experimentation. The US ag department spent over a million dollars to study the option. Japan has bought in, and already uses a third of its charcoal on farms. Brazil supports it in a few regions. The Maldives, threatened with flooding, recently signed on for projects on three islands. Australia, with soils low in carbon, is building momentum. Germany, the fast starter of green economics, already has a firm, the juwi Group, which began manufacturing biochar from crop wastes late in 2009.

In Ontario, a commercial greenhouse in Kingston produces biochar for interested farmers and other experimenters, says Helferty, who heads the industry association, Biochar Ontario, as well as serving on the leadership team of the Canadian Biochar Initiative. “Canada is quite far behind” on this breakthrough, he says. “There are no announcements of any funding, as far as I know,” he says.

My own smoldering hope is that cities will char the food and yard waste they now pick up, sell the biofuel, then offer the biochar to residents and parks staff for burial in their carbon-hungry soils, where 250 tonnes of carbon can be stored in every hectare of land.

Char may well become the new black, a way to combine measures that benefit climate protection, soil fertility, food and fuel production and job creation by making use of material that was once tossed off as waste.

(adapted from NOW Magazine, February 25-March 3, 2010)

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