Relax, fellow farmers and gardeners. From now on everything is going to come up roses and sunshine. A magical and mysterious soil has been discovered deep in the Amazon (roll of drums, please) that will double and triple your yields and grow tomatoes as big as basketballs. Not only that but this soil will sequester enough carbon to keep us warm through the entire coming ice age. Lean your ear close while I whisper to you the magic phrase. Shhhhh. Terra preta. Dark earth. In the ancient cities of El Dorado days, it meant salvation. For awhile.
And now you can have some for your very own garden.
I am sort of making fun of terra preta because of the money-mongers who would like to make a fortune selling the stuff to gullible Americans, but the story of this miracle soil really is amazing. Deep in the South American rain forest area there really are deposits of a mysterious soil as much as six feet deep in some places spread over thousands of acres. That of itself might not be remarkable, but anthropologists are almost certain that all of it, or at least most of it, was created by human beings in the centuries before Columbus blundered upon the American continent.
Actually there’s nothing much magical about terra preta beyond the fact that it was man-made. Archaeologists reason that it is the burned, or charred municipal wastes of lost civilizations whose populations numbered in the millions and who are now thought to have been very advanced. The black, sometimes brown, soil was made by burning food wastes, human and animal excrement, and a whole lot of wood. It is full of broken pottery shards which lends credence to the idea that it was originally municipal waste. Farmers who own deposits of it today still grow good crops on it.
Deposits of terra preta stand in stark contrast to the normal rain forest soil around them. The latter is shallow and of low fertility. Evidently, far back in history, humans figured out how to supplant these natural soils with terra preta, composting and burning their own wastes to do it. In that way they were able to meet the food demands of rising populations.
This magic soil is mostly charcoal, and scientists and entrepreneurs are making a new version of it which they call bio-char. You can find some for sale on the Internet. You can make your own by adding activated charcoal to compost or potting soil. The charcoal does make the soil more porous so that it will hold more nutrients and keep the soil more stable. It also will sequester carbon if you don’t subtract all the carbon emission created by burning wood to make charcoal. Soil scientists tell me not to get too excited about terra preta because while it is much richer than the rain forest soils of the Amazon region, our soils, especially our rich cornbelt soils, don’t need charcoal, or bio-char, at least not yet. In fact, the hot temperatures necessary for making bio-char volatilizes all the nitrogen out of it and so nitrogen fertilizer has to be added to it, sort of like when you use wood ashes for fertilizer. It is really more practical, soil scientists say, to make one’s own terra preta by composting organic wastes into humus in the usual way. Do it for ten thousand years and you will end up with deposits of mysteriously rich terra preta six feet deep.
So what happened to those marvelous farmers of the past who figured out how to make soil that could support high human populations? Many historians say it all ended because of the diseases that Spanish explorers brought to the American continent. But that is disputed because civilizations rose and fell several times before any Europeans arrived. It seems more probably that population growth kept outrunning the society’s ability to make more terra preta fast enough to keep up. The population crashed, then slowly increased again, with a new civilization adding more terra preta before it too over-populated, and that process repeating itself unto death do us part.
The Chinese with their careful utilization of all organic wastes were able to sustain a very high population density for something like forty centuries. But eventually they felt forced to make laws limiting family size to one child.
Terra preta does lead to all kinds of speculation. Maybe we should start char-burning our landfills to make fertilizer. Some municipal waste burning is being tried to generate energy. Maybe in 15 centuries our mountains of trash will be rich deposits of terra preta type soils. And all those humanoid creatures from other planets will be poking through them and wondering how our lost civilization could have been so smart as to create something so wonderfully fertile.