All Our Soil Problems Solved. You Bet.


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.


Eventually the sun is going to blow up… The things to be positive about are that continuing to drive up concentrations of greenhouse gases in the atmosphere is a near-term disaster for future generations of the vast majority of species and that making biochar is our only viable opportunity to lower concentrations and slow or otherwise diminish the damages. Gene, (thanks for your books),as long as there are woods on the planet, there are battles yet to be decided, and biochar knowledge and technology are much needed weapons!

After reading on this site and other places, I’ve become a little pessimistic. So, I’ve resolved to become more positive.

I’m positive things like this will continue to happen and eventually end up in disaster. Maybe not soon, but in time.

You might be interested to know that in Buddhist cosmology, “preta” are hungry ghosts, beings with huge stomachs and tiny throats who are doomed to always want more than they can get. There’s a message in there somewhere.

Actually terre preta could be the answer to global warming! The amount of sewage and garbage used to create bio-char not only would reduce the amount of carbon dioxide but could extract it from the atmosphere if incorporated in the soil. Bio-char can be made without pollution by saving the fluid and gas created to be used as a fuel to create more! In fact there are trucks available today that are fitted with a mobile unit to create bio-char on farms etc. and to return the char to the farmer and the liquid fuel and gas used to create more. There is no need to add nitrogen to organically farmed soils as this would kill the microbes that create nitrogen. In fact when rock dust, bio-char and compost are added to soil there is no need for any additives ever!

I’ve been following the biochar craze and wondering how much nutrient value it actually adds back to the soil. Good to know. Increasing the populations of helpful bacteria does sound like a good thing, though.

What interests me about the process of wood gasification (process used to create biochar) is the byproduct gas–a highly combustible mix of hydrogen, carbon monoxide, and other trace compounds. Powering a generator from a firewood is pretty neat, and if you can also capture the waste heat and get a useful soil amendment, all the better.

“The Chinese with their careful utilization of all organic wastes were able to sustain a very high population density for something like forty centuries.”

A generalisation, but not true. My understanding is that the China’s highest population before the wide spread use of coal & oil was 300 million, far less than the current 1.3 to 1.7 billion. I also understand that China’s population has crashed several times, sometimes by up to 60% to 90%.

I also understand that past climate change has driven this change, at least once. Different climates change the relative prosperity and power distribution between the rice growing south & wheat growing north.

Russ from Gene: I’m with you all the way. I’m not smart enough to understand how all that biochar enery trading chemistry acually adds up. And Peaksurfer, I wonder. If a reason for biochar stoves is to reduce rape in the woods, seems to me the battle is already lost. Gene Logsdon

The Epidra model is now being used by 20 or more industrial scale companies, many of them sellers of pyrolysis/gasification equipment. Some do CHP, some do just electric, some do CHP+biochar+bio-oils. One, which crash and burned from over-reach, tried to do CHP+biochar+bio-oils + golf-course community (carbon-negative putting). The biochar revolution will happen, widely, within 20 years, as peak oil and climate change force a retreat from mechanized chemical agriculture to carbon-farming. The Amazonians had the formula, as did the milpa and chinampa producers of Mesoamerica. Who got it seriously wrong was the Sumerians, with plows and irrigation, which begat John Deere and the plow that cut the plains.

If you can heat and light your house from scrap cellulose (nut hulls or chicken litter, for instance), smoke-free with 300% efficiency over wood, and are left with a charcoal skeleton of those scraps, that if blended with humus and “charged” then gives you an 800% increase in favorable soil bacteria and fungi over standard compost (to say nothing of NPK), why wouldn’t you? is putting biochar stove-making hubs all over Africa to improve the quality of indoor air, reduce rape (from wood-hunting forays), and reinvigorate depleted soils. They want to be up to 1 million stoves per year by 2012. Si se puede.

I remember being at a conference a couple years ago where one of the break-out sessions was about terra preta. I had never heard of it. The thing I recall that struck me most was that the charcoal itself is not a particularly soil enriching amendment. The thinking was that the microscopic honeycomb structure of the charred matter created a great host environment for micro-organisms whose activity is beneficial to plant growth. Soil enrichment through promotion of bio-diversity – that’s a nice concept. Monsanto probably has a team of lawyers working on excluzive patents right now. Thanks for the broad range of topics applicable to contrary farmers.

Regarding biochar, there is a variant of this being worked on by a group called “Eprida”. Their concept is to burn wood or other high-biocarbon material just hot enough to gas off the complex organic molecules and burn those gases very hot and efficiently to extract some energy from them. Part of that energy is used to keep low-burning the incoming wood or etc.; with the rest of the wood-gas energy used to generate electricity. The unburned solid wood-carbon (charcoal) would then be mixed back into the soil the wood (or other plant-carbon source) came from.

Even taking into account the carbon released by burning wood down to charcoal to mix powdered charcoal back into the soil; the process does net-lower carbon in the air a little bit. Because the tree sucked carbon out of the air to grow its wood; and burning it for charcoal releases only some of that air-carbon back to the air. The rest of the air-carbon remains sucked out of the air as charcoal which remains semi-stable in the soil if mixed there. And each cycle of grow wood/ semi-burn wood/ bury charcoal sequesters another net charcoal-load of carbon down into the soil.

The nitrogen lost into the air by charcoaling the wood can be sucked back down by legumes and non-legume methods of bio-fixing Nitrogen.

So if we set aside our desperate hope for miracles, we can view this as a useful method if applied widely enough long enough.

Teresa Sue Hoke-House January 2, 2010 at 2:18 pm

We can wish that everyone would do the right thing concerning their land, until the cows come home. The truth of the matter is that it will be up to each of us as individuals to leave our little plots of land better than we found it.

Gene, you had a line at the end of “The Gardener’s Guide to Better Soil” that really inspired me – something to the effect of “a person could accomplish nothing more important than to improve 1 acre of land.” I’ve always found it amazing that soil can be created yet fertility dwindles away due to bad management. Why aren’t we mining landfills, the ocean and our own kitchen wastes to turn dust into food? Why aren’t big farmers using more inoculum and finding sensible uses for all that feedlot manure? Who knows.

I have to disagree with you about your Malthusian view on population density – especially with China, whose 1-child policy was on direct orders of the Rockefeller foundation. The world produces more food per capita today than any known time in human history. Imagine what we could do with proper cultural practices.

Soil-building and biological agriculture should be considered high science, as opposed to the low-grade chemical dumping and GMO “science” we see today. Man is the only animal than can expand his environmental limits. The ingredients for better soil and sustained population are just lying around and floating through the air, waiting for a wiser culture to put to work.

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