[gost]

Oh man, am I glad I found you guys! I've been trying to figure out how to make terra preta since I saw the BBC documentary a couple of weeks ago and just ran across your forum during a google search.

Michaelangelica- I ran across the article by Scott Bidstrup, apparently quoted on the Gary Jones site, where he contemplated building a solar oven for making low temp charcoal. He seemed to feel that the trough of the reflector needed to be about 8 to 10 feet wide in order to achieve the 470 F needed to make the charcoal. It almost seems like he is guessing at this, but I can't tell for sure. It seems awfully big to me, especially since Bidstrup is in Costa Rica, but I don't have any experience with this type of collector. Are you basing your design on an existing concept that has calculated the temps for different latitudes? Is there a simple formula for calculating the parabola? I'm very excited to follow your results.

My thought was to cut two pieces of half inch plywood into the parabolic shape, making the ends of the trough, then simply use a staple gun to attach the mylar posterboard to the edges of the plywood, thus eliminating the need for any ribs. The pipe itself would then go through oversized holes in the plywood, at the height of the focal point, where it would then be kept from touching the wood by the use of 3 adjustment screws.

I had also been planning on using galvanized stovepipe, of the kind used for gas water heaters. Does anybody know if the galvinizing might introduce anything toxic, when heated, that might absorb into the charcoal?

On another note, I'm having trouble with the concept that all the nutrients taken up by my veggies could be replenished by just rainwater alone on any sustainable basis. Is this really credible? In the Amazon, it must be possible to grow crops on a year-round basis. That's a huge amount of nutrient removal to expect to be replaced simply by rainwater alone, especially with the claims of a 300 percent increase in productivity with terra preta. Has anyone run across any real research to support this idea of rainwater as fertilizer?

As far as the microorganisms involved in terra preta, does anyone know if they are particular to the tropics? Might the organisms involved here be similar to the biotic community found in any well maintained compost pile? I currently make two types of organic compost: regular and vermiculture (worms). My thought was to replace some or all of the browns in my regular compost with finely ground charcoal made from chipped fruit tree prunings, woody brush, and alder branches. That way the charcoal would perhaps already be hosting a microbial population when I add it to my garden soils. Any thoughts on this idea? If the community is more specific, could real terra preta perhaps be used as a microbial starter? I read that Amazonian locals have been selling terra preta as potting mix for years. Does anyone know of an internet source for buying a real sample of this stuff?

As far as the charcoal itself, is there a difference between wood based charcoal and that made from garden material, such as, for instance, corn stalks? Are the resins involved any different? It seems to me that if the ancient Amazonians were making their charcoal from the material derived from clearing the land itself, it would have been mostly made from tropical hardwoods.

I'm not sure what the pottery might have added to the whole mix, but I do know a couple of potters that always have a pile of broken pots laying around who would be more than happy to get rid of the stuff. As I recall, their initial firing of the clay, before the final glaze firing, is done at a relatively low temp. Perhaps broken bits from that firing would be more akin to the shards found in the Amazonian sites.

LOL. I have about a million more questions, but I better leave it at this for now. Gardening season is just getting started here in the Pacific NW where I live and I can't wait to do some experimentation. Thanks to everyone that's been posting to this thread. I'm glad to learn that I'm not alone in the level of excitement generated by the potential implications of this new/old technology.