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["Frank Fries" <frank.fries AT imagewireless.ca>]

> out, it seems, that the charcoal is incidental.  The archeology of the 
> patches
> show that they were intensively gardened continuously for 3000 years and 
> that's
> why they are permanently fertile.   >

Having read a fair bit on this, and having read about the various 
experiments in pots with differing percentages of charcoal, etc.  it doesn't 
appear that anyone really knows why the soil is permanently fertile.... 
however, as you said, just adding powdered charcoal definitely doesn't do 
it.

In the Amazon basin, when they dig some of the Terra Preta up, as long as 
they only take a little at a time and leave enough in the patch, it seems to 
"grow back"...  This implies that it is related to beneficial 
micro-organisms... There is some speculation that the porous nature of the 
charcoal helps by providing a beneficial environment for the soil 
micro-organisms.

In one case that I read about (it was a while ago and I don't have a link to 
it - this is from memory only) they tried a number of patches in the Amazon 
basin, in the poor soil  - a control plot (no change to the soil), a plot 
with chicken manure added, a plot with charcoal added and a plot with 
chicken manure and charcoal added.  (I think there were actually a number of 
plots in each of the categories above, with varying amounts of manure and 
charcoal added).

As you would expect in infertile soil, the plot with the chicken manure 
added did better than the control plot.  It also did better than the control 
plot in the second year but the improvement was less marked and even less so 
in the third year.

As I recall the plot with the charcoal added was slightly better, but not 
much so compared to the control plot.

The plot with the charcoal and manure was approx. the same as the chicken 
manure plot the first year, but noticably better the second year and even 
more so in the third.  There appears to be a cumulative effect.   This may 
possibly be due to micro-organisms getting a chance to breed up and perhaps 
the charcoal assists in some way.

None of the above is conclusive and it certainly doesn't necessarily mean 
that the same thing would work here...it is possible for example that there 
very specific micro-organisms that exist there and not elsewhere, or ...??

Another thing I once read was about the beneficial effect of animals on 
soil.   I think everyone (even the agri-biz soil scientist types) agrees 
that organic matter added to soil is good.  At the very least, it produces 
nitrogen.  There have been studies proving the negative effects of cropping 
land and taking all organic residues off (the straw, stalks, etc).

In the study I read about, they used a number of fairly large plots that had 
been farm land, and they seeded all but one of them to some kind of forage. 
The unseeded one was kept fallow.

In one plot they just let the cover crop (hay/grass) grow and stay on the 
land, eventually decomposing ( I can't recall for sure, but I think they may 
have cut it and/or chopped it).

In another, they harvested the hay (and hauled it away).

In yet another, they harvested the hay and fed it to animals, whose manure 
went back on the soil.  I can't remember for sure but I think that they let 
the animals harvest it directly (graze), which of course also looked after 
spreading the manure.

So on the one plot, nothing was taken away from the soil, on the second, the 
weight of the hay was taken away, and on the third, the weight of the 
grazing animals turned into meat was taken away from the soil.

If it were just volume of organic material, you would expect the piece with 
nothing taken away to be the most fertile after the trial.  As I recall, all 
the seeded test plots were more fertile than the fallowed plot after the 
trial and the most fertile was the one that had the animals and their 
manure.  It appears that perhaps the digestion process used by animals adds 
benefits beyond just the organic material in the manure.

It appears to me that none of this is just cut and dried, and as the soil, 
moisture and weather changes from one area to another, different rules 
apply.  It sure is interesting though.

I look forward to experimenting with different things over the next few 
years as I get a chance to.... One of the things I mean to try is raised 
beds.

Frank