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In a Wednesday session on using biochar as a climate stabilization measure, Nathaniel Mulcahy of World Stove explained that over 2 billion people worldwide cook on open fires. Constant open fires not only pose a carbon emissions problem, they pose a health risk, increasing respiratory distress and incidences of asthma. If they cooked their meals on a simple pyrolysis stove, instead of an open flame, they could sequester between 1-3 tons of carbon per person, per year, which is about what you'd get from an acre of pine forest, and significantly reduce indoor particulate.
Along the same lines, Mulcahy noted that 20 million tons of rice straw were just burned in Egypt every year. Ash from open fires retains as little as 3-5% of the original mass of carbon in the original plant material, and the nutrients are used up quickly. Char produced through pyrolysis, on the other hand, can retain 20-50% of the original mass of carbon, which can then stay in soil a long time and improve fertility.
And here, I should mention the ways in which combustion (burning things), digestion and decomposition are all similar. Each of these processes take carbon that was originally breathed in by plants, solidified by those plants into sugars, possibly eaten by a series of animals, and then returned to a gaseous state in the form of carbon dioxide (CO2) or methane (CH4). Having mentioned digestion and decomposition separately, I should proceed directly to tell you that decomposition is a word for digestion by microbes (bacteria and fungi,) and so while we think of it separately, it works about the same and isn't some inevitable, mechanical process.
The climate-relevant question is how quickly this cycling of carbon on land and through organisms (pdf) proceeds and how much of it is going on at a given time.
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| Also, having said how they were alike, I should explain a major difference between the digestive byproducts of animals and insects and digestive decomposition by bacteria and fungi. Animals process food very incompletely. You've seen the evidence. When a host of fungi and bacteria get done eating, even what's considered waste by other life forms is reduced back to gas and, which is key, extremely inedible carbon compounds (humus) that you could unhesitatingly run your fingers through and pronounce to be good, clean soil. That's what compost is.
Biochar, produced by high temperature, low oxygen pyrolysis, is organic material fired into extremely inedible compounds, retaining between 20-50 percent of the original mass of carbon in the form of black carbon that functions much the same way as humus. While black carbon is harmful when suspended as an aerosol, Mulcahy explained that black carbon acts like a coral reef for life in the soil, while pyrolysis still reduces emissions from fires overall. Further regarding emission byproducts, Lehmann said that noxious aromatic hydrocarbons and dioxins are usually produced at over 700 degrees Celsius, while their recommended guidelines for biochar pyrolysis suggest that the temperatures be kept in a range below that.
Char can also remain in the soil for hundreds or thousands of years, uneaten even by bacteria. Not only are the original Amazonian Dark Earths still fertile and thick with char sometimes 2,000 years after being laid down by indigenous peoples, but researchers have found fertile ADE soils with evidence of having been farmed continuously for hundreds of years.
Applied to soil, Dr. Johannes Lehmann of Cornell explained that it offers the benefits of reducing nitrogen emissions from soil, increasing methane uptake, and when applied correctly, increasing soil pH in acidic soils. The char material's physical properties reduce soil density, hold on to nutrients better, and soak up a lot of water - all of which add to land's productive capacity and can cut runoff.
Lehmann said that while there have been cases where biochar didn't work as a soil amendment, it's like anything else you buy for a garden and needs to be right for your soil and nutrient conditions. The wrong kind of any sort of compost or fertilizer, or the wrong amount of water, and you can harm the plants in any garden.
Mulcahy added to this while discussing the range of materials that char can be made from. He said that you could produce very low nutrient chars that were good if all you needed was the physical properties, though chicken litter char was very high in phosphorus and might be indicated if your soil needed a phosphorus amendment.
In field trials in Senegal, Guy Reinaud of Pro-Natura said that while he was waiting to have another full year of results, they've seen yields triple after char application. They're now recommending that interested farmers simply add char to normal practices.
While char has been proposed for a wide range of uses, Lehmann's recommendations seem modest. He suggest production on a small scale, locally and on-farm, using cheap agricultural wastes, trimmings and invasive plant species.
Reinaud reinforced this view, saying that the most economical use of biochar technology was the reprocessing of agricultural waste, as it was much more efficient than getting char from cutting down trees. Which is important, he explained, because as much as 90% of charcoal production for fuel use in Africa causes deforestation. He said that the reeds along the rivers in Senegal contained enough biomass for most of the country's energy use through pyrolysis, after which presumably, the char would be left over for adding to the soil.
Though as Lehmann said, biochar needs to be incorporated into a systems approach to land management, and subjected to evaluation and carbon credit measurements that ensure all use is truly beneficial. "It's common sense," he said, "that any technique could be used well or badly."
Update: minor addition to an incomplete sentence. |
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