I have my own theory about the invention of Terra Preta.
Once upon a time there was a young genius who was tired of eating raw fish, and was tired of being cold and wet...
It rains a lot in the Amazon during the rainy season.
Hoard wood in your hut if you like: you'll run out long before the rain passes.
With every bit of burnable wood soaked, folks eventually ended up eating their fish and veggies raw, until the rains ended and the fuel supply dried out.
Now, pottery kilns had been invented long before. The first kilns were probably hollow logs.
Set the pottery in the hollow, set the log on fire and you get a fairly even heat. When the log is burnt away, you have your fired pottery.
Someone no doubt invented a shortcut, MAKING a hollow "log".
They built a large basket from green reeds, and set it over a firepit. They put the pottery inside, coated the basket with clay and kept the fire going until the basket self-destructed.
The bits left over from the basket would be charcoal by then...
And it's not a leap to assume that people would know that charcoal makes a good fire, if you only have enough of it.
So our young genius already knew how to make a kiln, and knew that charcoal would be valuable.
So he invented a kiln to do just one thing: to make charcoal.
He built a stack of wood, and covered it with green reeds. He slathered the reeds with clay, leaving a hole at the top and a hole at the side.
He lit the stack on fire through the side hole and watched. The fire climbed up through the stack, hardening the clay as it baked the water out of it.
Finally the color of the smoke changed from yellow to blue. He blocked up the holes and waited.
Eventually the kiln cooled. He broke it open with a stone and voila´! It was full of charcoal.
He then realized one thing: he was going to be rich.
He built more kilns, refining the technique as he learned. Finally, the rainy season returned.
He broke open a kiln and started selling charcoal, trading for fish and fruit.
His idea was a smashing success !
People came from all around, to buy charcoal so they could have a cooked meal.
Franchises popped up everywhere, of course.
Not all of the charcoal was salable, though.
When large pieces were broken up for sale, some little chunks and charcoal dust fell to the ground, mixing with the broken pottery shards everywhere.
Traffic ground this detritus into the soil. Our genius left it there: it's not as if anyone would pay for little bits and powdered charcoal anyway.
Eventually, though, our entrepreneur had a problem. He'd used up all the available wood in the area.
Los Indios didn't have metal tools to chop down trees, saws to cut them up, nor the horsepower to drag the trees very far.
It was easier to move his operation to a new source of wood and transport the lightweight charcoal to his customers.
His fire-pit was abandoned. It became used as a rubbish tip and soon was overflowing with garbage, fish bones, manure, etc.
The garbage became compost, and turned into organic mulch.
Earthworms came along, and slurped up the mulch to get at the bacteria living in it. They actually ATE the charcoal powder in doing do and ... spread it around as they moved on.
Eventually someone planted a garden there. It was an old trick, and always got a couple of years of good harvests... until the rains washed the nutrients away.
So it was nothing new. Until the plants in the new patch took off like skyrockets ! Year after year, the harvests were amazing. And the harvests didn't fail, as they always had.
It must have been like magic to Los Indios.
The thin clay in the Amazon is poor soil, even weeds don't grow well.
But the invention of Terra Preta changed all that.
The new soil had different cation exchange rates, moisture retention abilities, and rather than vital nutrients being washed away by the rains, the biochar retained them.
The soil bacteria had colonized the voids in the charcoal, just as the ancestor to our DNA molecule may have colonized the layers between mica in watery environments in the primordial oceans.
That soil bacteria helped maintain the fertility, by breaking down minerals trapped in the soil into forms plants can use. Silica, calcium, and iron.
Other people tried to copy the success of that first patch. Maybe some succeeded; maybe not, if their charcoal wasn't "inoculated".
Until someone snuck into the first Terra Preta patch and stole some of the "magic" dirt.
They mixed this into their own fire-pit/garbage tip/garden patch soil and voila´!
It worked ! Hurray !
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So that's how it happened. Once people figured out how to repeat the process they went commercial with it.
Terra Mulatta is that commercial version: wood and weeds charred in the fields JUST before the rainy season, to prevent the fires from spreading, and to extinguish the biochar before it burned to ash.
But do the pottery shards in Terra Preta actually DO anything?
Probably not. The soil base is already clay: the pottery shards are just fired clay stained by woodsmoke.
Woodsmoke has been shown to stimulate some seed germination, but it would have washed away after a few years.
Unless someone does a controlled experiment and proves that soil fungi colonize the pottery shards, I'm guessing they're not necessary to Terra Preta Nova.
Re: The clay shards and pottery in TP What & Why?
