By Bart King
When it comes to climate change, every potential solution seems to have a downside. For example, biofuels that could offset petroleum divert food stocks and/or have the potential to degrade ecosystems. Solar power is intermittent, requires the production of toxic materials and gases, and is still prohibitively expensive. And wind turbines are considered an eyesore by many and a threat to winged wildlife by others.
However, biochar might be different. Despite a rather unpleasant name, which calls to mind road kill on hot summer day, it has refreshingly unspoiled promise. Admittedly, research into the production and use of biochar—also known as agrichar—is not yet widespread. It could still prove to be a bad idea—producing, for example, a breed of oversized zombie earthworms. But so far things look good.
Simplicity is its greatest virtue. First of all, biochar is just another name for charcoal. It’s produced by burning any biomass under high temperatures and with very little oxygen—a process called pyrolysis. Roughly half of the carbon from wood chips, manure or crop residues fed into the oven is converted into synthetic gas or bio oil, which can be used as fuel or in co-products like cosmetics. The remaining carbon is turned into charcoal, which is resistant to decomposition for hundreds of years, assuming it isn’t used to fire up the grill.
Estimates suggest that 7 to 12 billion cubic meters of biomass from fields, pastures and rangelands are burned in the open each year, creating soot, nitrous oxide, ozone and other pollutants. Additionally massive amounts of crop residues and animal waste are allowed to decompose into the greenhouse gases carbon dioxide (CO2) and methane. Converting this biomass to biochar has the potential to reduce these emissions and over time could actually remove CO2 from the atmosphere by breaking the cycle through which decomposing plants emit CO2 that they captured while growing. As a result, biochar has been labeled “carbon negative.”
So what do you do with all the blackened carbon? Bury it of course. Not the way we bury trash—and infinitely less expensive than carbon sequestration plans touted by the coal industry.
Biochar is a valuable soil amendment first used by indigenous cultures in the Amazon Basin centuries ago to improve the fertility of barren lands. The porous charcoal retains moisture and encourages the proliferation of microbes that are critical to soil health. Mixed with topsoil, biochar can reduce fertilizer requirements and the leaching of nitrogen into ground water, while increasing crop yields.
The Amazonian soils—called terra preta, or “dark earth,” by Portuguese explorers—are said to contain about 80% of the carbon sequestered in them 500 years ago. Studies have revealed between 16 and 108 tons of biochar per hectare and 400 to 500 tons of organic carbon in the form of humus, bacterial biomass and fungal roots. So, it seems that the overall carbon storage capacity of these soils is significantly greater than just the biochar itself, which acts kind of like a carbon magnet.
