29 July 2008
We’ve read about how archeologists, ecologists, and soil scientists have studied areas around the Amazon river to try and understand the cultural and agricultural uses of biochar as long as 2,500 years ago.
An article in Discover magazine — “Black Gold of the Amazon” — discusses these contexts, and helpfully for our purposes, examples of the biomass makeup and a distinction between “smoldering” (the first step in carbon sequestration) and more traditional slash-and-burn agriculture:
The terra preta soils at Hatahara and the other sites are made from a mixture of plant refuse
and animal and fish bones, along with large quantities of charcoal that were deposited after settlers used stone axes and slow-burning fires to clear forest. Such smoldering fires produced more charcoal than ash. The charcoal, soot, and other carbon remains (collectively called biochar) retained nutrients, particularly potassium and phosphorus, that are limited in tropical soils. The resulting improvement in soil fertility may have allowed the land to support a larger, more stable crop-based population, although studies of fossilized pollen have not yet revealed the specific plants they cultivated.
In addition, soil scientist Johannes Lehmann is quoted in the article as arguing that in integrating biochar in agriculture, “you wouldn’t just be carbon neutral, you would be carbon negative, drawing carbon dioxide out of the atmosphere, producing energy and improving the climate in the process.”