Jim raised a good question regards the last post:
Ulf, I am wondering why you say you are just doing the "Terra pretta" treatment for a couple of seasons while I understand the traditional Amazons seem to do it most years in the same area of their gardens.
In recent months I have had a couple of fires going to boil water and as soon as I was finished I was able to pour water over the remains of the fires and both times ended up with a bucket or so of "clinky" sounding charcoal. It is in the interow area of the garden so hope it is doing good for the vegies.
We also live in an area where we rely on indoor winter fires for heating. We keep over burning our fire box day after day and end up with just white ash. I know others in this area who insist on emptying out their fire boxes daily, and in so doing throw out a lot of charcoal and they just dump it, throwing away a valuable garden resource.
In principle the charcoal puts a layer of carbon into the soil which in turn creates an environment for the bacteria that create Terra preta. Even though the charcoal will be gone in a decade or so, the soil will be changed and become self renewing. Tests have shown that when black soil is removed from the beds in the amazon it actually grows back over time.
I suspect the annual burning by the Indian peoples in the amazon was to gradually enlarge the beds each year rather than continue enriching the same beds. I was not aware of any of the peoples living in the Amazon still creating these beds. I note that many of the original beds were very deep, sometimes over six feet deep! This would require a lot of burning indeed. Possibly this meant a concentrated effort for several seasons in the same area.
In reading about the old ways of farming I constantly find references to farmers using the ash from the fire in their fields. White ash yields potash of course and the charcoal enriches the soil as described above. To throw it out would be a dreadful waste. Perhaps your neighbours would give you their ash if they are not going to put it to good use?
One very interesting old process describes layering the white ash from the fireplace with chicken manure in barrels over the course of winter. Come spring this is then broadcast over the fields for a sort of super mineral compost. Apparently the time it has to age together increases its potency. I will really have to try this sometime!