Summer 2008 Climate Alert
Climate Change & Food Security [ PDF ]
In this Newsletter:
A Closer Look: Bio-Char
Charcoal has traditionally been thought of primarily as a fuel and is still widely used throughout many developing countries for that purpose. However, scientists studying the abundantly fertile terra preta de indio (black soils) of the Amazon now feel that charcoal has been, and perhaps should be again, used for another purpose: as a soil additive. Their evidence seems to indicate that for centuries the indigenous tribes had intentionally mixed charred biomass into the local soils. Findings show that using bio-char (as the agricultural charcoal is being called) in this way not only boosts fertility but also holds great potential as a means to sequester carbon.
Bio-char forms as a result of anaerobic heating of biomass in a process called pyrolysis. While normal combustion (burning) of biomass results in the immediate emission of 97% of its former carbon content into the atmosphere, and biomass left to decompose naturally loses up to 90% of its carbon within 5 to 10 years, biomass subjected to pyrolysis emits only about 50% of its former carbon content and transforms the rest into bio-char in such a way that it will not reenter the atmosphere for an estimated 5,000 years.
While more research has to be done to answer questions about the ideal composition of biomass feedstock, the optimal amount of bio-char to be added to different types of soil, the potential for making bio-char production from urban waste, and the possible negative effects of bio-char addition on soil (such as leaving less nitrogen available for crops), there is strong consensus that its benefits to soil fertility include increasing water and nutrient retention, attracting microbes, and absorbing ammonia. Weathered, nutrientpoor tropical soils seem to gain the most (up to 80% fertility increase) from bio-char addition.
Since the costs of producing bio-char from scratch currently outweigh the benefits it can provide as a soil enhancer or carbon sink, the key, for now, is in finding ways to produce usable bio-char by modifying processes that would be carried out anyway. For example, by replacing the much maligned but widely used, slash-and-burn method of clearing land with a slash-and-char technique, total anthropogenic carbon dioxide emissions caused by land use could be cut by as much as 12%. Consider also, the case of agricultural waste. While it is now burned or plowed into the earth, it could instead be turned to bio-char. Doing so would not only improve soil fertility and safely sequester carbon in the earth but also, by virtue of the bio-oil, methane, syngas, or hydrogen by-products of pyrolysis, create usable, carbonneutral energy.
Other Articles in this Newsletter:
Climate Change & Food Security
A Message from the President: Fishes, Loaves and Foresight
The Challenges of Producing Food on a Warming Planet
Reducing Our Food's Impact on Climate Change
Focus: Moving Down the Food Chain
Case Study: Agriculture in Thailand
The Biofuel Debate: Food vs. Energy?