After doing previous charcoal experiments, (check out the Charcoal Category), I’ve decided that this will be my first year to put charcoal over my entire garden. It will be interesting to see how long it takes to break down so I can incorporate it into my soil. There may be a PH, soil acidity, problem, but I will have to watch and see what happens with charcoal. I ended up using 100# of charcoal for all my gardens. Note – I have found at least one brand of briquettes, Wicked Good Charcoal, say that they only use corn starch as a binder. Other sources seem to have a few more ingredients, but nothing terrible.
Here are a few more sites I have found about Terra Preta
- Terra Preta Gardens
- Stanford University-Youtube
- Slides from above
- BioChar FAQ
- http://www.biochar.info/biochar.biochar-overview.cfml
- Soil Biology & Biochemistry 39 (2007) 684–690
- Cornell University 1 – 2
- The Science Show – Australia
- Mother Earth News
- Nature Magazine
- Information for Schools
- FAQ-Gardening with Biochar
- The Biochar Solution: Carbon Farming and Climate Change
- The ‘Terra Preta’ phenomenon: a model for sustainable agriculture in the humid tropics
- Biochar for Environmental Management: Science… (Hardcover) by Johannes Lehmann, Stephen Joseph
- BBC Article
- University of Hawaii Article
- MAKING BIOCHAR: with Peter Hirst of New England Biochar – makes the point that charcoal will compete with plants for water and nutrients so he mixes it with compost and water for a couple of weeks before he adds it to the soil. I’m not worried about this since I will later add compost and fertilizer.
Butterfly Gardening 
Are you using charcoal briquettes like you use in a grill?
I am using regular briquettes.
While I’d like to use “natural” charcoal,
my experiments show that it just does not break down
and you would have to manually break it up with a brick or something similar.
Briquettes have a water soluble binder which breaks down over time.