Saving The Planet While Saving The Farm

How soil carbonization could save the planet while it restores agricultural profitability

A personal essay in hypertext by Scott Bidstrup

It is not enough to try to browbeat business as well as the population into giving up fossil fuels... Fossil fuels are simply far too convenient, cheap and easy to use for their use to end anytime soon, no matter how repressive government gets. If we are going to solve the problem of global warming, it won't happen by denying the problem, as conservatives tend to do, or by browbeating people into spending more money on less convenient alternative energy sources, as liberals would seem to prefer. The only realistic solution - what must be done - is to make the addition of carbon dioxide to the atmosphere a non-problem.

For a long time, soil geologists and archaeologists faced a mystery.

The mystery was a nagging one, but not an urgent problem that impelled soil scientists to travel to the Amazon jungles to solve. But it was an intriguing problem which was finally solved by an archaeological survey - a survey which involved soil geology.

For many years, it had been known that among the extremely weathered and infertile soils of the Amazon basin, some of the least-fertile soils on the planet, there are large, widespread patches of highly fertile soil. Soil that is not just fertile, but extremely fertile - so fertile and so valuable that for many years it has actually been mined and exported as potting soil for gardeners. What was the difference? The only visible difference was that the fertile soil is black, pitch-black, and grew just about anything with ease, and the infertile soils, just a few meters away, are a pale yellow color, and are so infertile that almost nothing except native weeds can grow in them.

Archaeologists entering the Amazon in the 1870's noted patches of dense forest surrounded by savanna scrublands and noted that where the forest patches grew, the soil was black and rich, and there were also abundant pottery fragments, apparently left behind by pre-columbian aboriginals. But outside the forest patches, the earth was the yellow clay oxisol that is dominant in the Amazon basin. They discovered that there were not just a few, either, but there were many such places. In the black soil, the pottery fragments were often so numerous that they made up as much as ten percent of the soil volume - but the pottery fragments only occurred where the soil was black. The source of the pottery fragments was a considerable mystery to the archaeologists, as nothing was known about where they came from or how they came to be there in such abundance. So a few years ago, archaeologists undertook a survey of the black earth ("terra preta do indios" ("black earth of the Indians" as it has come to be locally known) areas to determine just where the pottery came from and how many indigenous peoples must have been living in the area.

The results of the survey were startling indeed. The black earth areas, about twice the size of Great Britain, possibly as large as France together had supported as many as three million people - more than had been believed to have ever inhabited the entire Western Hemisphere at any one time. They had realized that the black earth was fertile, but had never imagined that the Amazon basin could be so hugely productive.

The survey solved another mystery, too, this one a historical mystery. In the year 1541, the first European exploration of the Amazon river occurred when Francisco de Orellana, a Spanish conquistador, floated down the Amazon river from a tributary in the Peruvian Andes to the mouth in the Atlantic, a distance of more than five thousand miles. The privations of the journey, lack of food, prevalence of jungle diseases and the like took their toll, and the crew of Orellana's expedition died, almost to a man. By the time he returned to Spain to tell his tale, he alone remained. His epic story included tales of huge cities, with markets bulging with foods of every description, and of course, gold. Orellana's tales contributed greatly to the legend of El Dorado. But when the Spanish finally returned to the Amazon eighty years later, all they found was empty jungle, with a few scattered natives subsisting off of the rain forest. Oreallana's descriptions were dismissed as fantasy by generations of historians. Impossible, they said, couldn't have happened.

What we now know is that the Amazon did, indeed, support large communities of aboriginal peoples, just as Oreallana had said, which seem to have mysteriously vanished into the hunter-gatherer tribes seen by later European explorers. But we also know, from archaeological evidence, that they may (and probably did) survive into post-Columbian times, only to quickly disappear. And it was apparently the disease brought by Orellana and his men that caused the sudden decline, as European contact did in so many other places. When the cities were swept by disease, they were abandoned, and the jungle quickly swallowed up the sites, leaving nothing behind for explorers to find eighty years later. So, as we now know, the legend of the rich cities of the Amazon did have a basis in fact. And it was the terra preta, the black soil, which sustained that vast culture, that was the real gold of El Dorado.

All this got the curiosity of the archaeologists really going. What could possibly make the difference - why was the terra preta so fertile, when the soil around it was so sterile? They finally felt compelled to call in soil geologists to find out. And the discovery they made astounded them.

The soil scientists studied every possible aspect of the black soil - its minerology, its geological history, its chemistry and its physical structure, but what they discovered was truly amazing to them as well as to the archaeologists. The mineral content of the soil is identical to the sterile yellow oxisol clay in the surrounding areas - there was no geological or mineralogical difference. The only difference between the sterile yellow clay of the Amazon river basin and the incredibly rich and fertile terra preta of that region is the presence of finely divided charcoal powder in the terra preta.

Apparently, the indigenous farmers of the region had taken to carbonizing their farm waste, grinding the charcoal to a fine powder, and adding it to the soil. The richest soil samples, those with the greatest fertility, were between nine and forty percent charcoal by volume, and the charcoal was powdered to a fine powder - a few hundred microns was the average particle size. There are few bits of charcoal any larger than a quarter of an inch in size. The charcoal was produced in a low-temperature process, not heating it too excessively. It contained within its molecular structure plant resins that had been heat stabilized by the pyrolization process.

Because nobody had ever bothered to investigate powdered charcoal's effects on soil fertility carefully, soil scientists had simply always assumed that charcoal when added to the soil, was inert and its effects primarily mechanical. Chemically, it is very stable at ambient temperature - even on geological time scales - and does not participate in chemical reactions, so it was simply assumed that any nutrients it trapped were simply unavailable to plants. Close investigation of the terra preta situation proved this to not be the case. Not at all.

What the soil scientists, working with microbiologists, discovered was that a community of bacteria exists in symbiosis with the root hairs of plants in terra preta soils. The bacteria produce enzymes that release the mineral ions trapped by the heat stabilized plant resins in the charcoal and make it available to the root hairs of the plant as nutrients. In return, the plants secrete nourishment for the bacteria. Not only that, but the resins within the charcoal act like an ion exchange resin, adsorbing traces of mineral ions onto the charcoal particle surfaces from the rain water, and trapping it within the charcoal's molecular structure, where it can be held for centuries - until the soil bacteria associated with a root hair come along and secrete the enzymes necessary for it to be released once again. So the trace minerals always present in rainwater actually act as a fertilizer - providing the nutrients needed by the crops, year after year. The secret of the soil fertility of the terra preta was finally understood. And it was understood how the indigenous farmers were able to produce bumper crops year after year, decade after decade without a single application of chemical fertilizer and without wearing out the soil.

This was confirmed when the soil scientists grew some test plots. The results were seen recently on a Discovery Channel special about this Amazonian mystery. Viewers saw three plots - the first, the control plot, was natural Amazon yellow soil from which the native vegetation had been removed. The second was identical to the first, except that chemical fertilizer was added. And the third was a plot identical to the first, but to which charcoal was added along with a normal dose of chemical fertilizer. The results were dramatic. On the entire control plot, there grew only a single plant, pathetically stunted, which did not flower. On the fertilized plot, there was a small growth of stunted plants, few having produced seed heads - clearly what could only be described as a failed crop. The charcoal plot was dramatic - lush growth with an abundant crop of seed heads - a bumper crop indeed.

This discovery also solves a mystery that has puzzled farmers in tropical regions for years. It has long been known that growing sugar cane increases soil fertility. Over the years, soil in which sugar cane has been grown can become quite fertile - the opposite of what happens with nearly all other crops, which tend to exhaust soil. We now know the reason why - sugar cane fields are normally set alight before harvesting. The flames sweep through the field, burning off the thicket of leaves and leaving only the cane behind, making it much easier to harvest. What is left behind also includes a small amount of charcoal, which finds its way into the soil, gradually adding to its fertility, year after year. Where I live in Costa Rica, sugar cane, which is a low-value crop, is often grown simply to keep the farm alive and sustain the soil, while the farmer tries to find an alternative use for his land. It is a sad situation, but now there is an alternative. It is to make the land economically productive once again, by doing deliberately what the cultivation of sugar cane does accidentally.

Saving The Family Farm

If the required amount and type of charcoal is added to soils in tropical and semi-tropical regions where these symbiotic bacteria are normally present in the soil, the chemical inputs required to sustain agricultural productivity can be greatly reduced. In temperate regions, manure and composted field waste can be added to kick-start the growth of these organisms and get them established in the farmer's soil as a normal part of the soil fauna and flora.

Of course, this gives such a farmer a considerable advantage in economic terms over his competitors - while his competitors are spending large amounts of money on chemical fertilizer and other soil amendments, he is spending nothing - only the cost of carbonizing his farm waste, grinding the charcoal to a powder, and tilling it into his soil, and then only till the optimum level of carbonization is achieved. And as we shall see, this can be done at an acceptably low cost, even by farmers in developing countries. An additional marketing advantage is that he can maintain soil fertility in an organic manner, helping greatly in certifying his farm as an organic farm, which can mean an increased value for the produce he sells. Soil amendments, primarily fertilizer, are by far the greatest single cost that a farmer in the tropics faces. With proper soil carbonization, that cost simply goes away. Farms that were economically marginal or failing, now can suddenly become not only highly productive, but highly profitable. Instead of selling the farm that has been in the family for generations, the struggling farmer now has the option to go back into farming - and make more money than he could ever hope to make by working for wages or struggling to compete in the city.

Carbonization of farm waste has traditionally not been practiced, because it has traditionally been slow, inefficient, messy, labor intensive and produces a product for which, until now, there has never been enough use to justify all the trouble - and it has always been assumed to have limited value as a soil amendment. It has always been easier to just plow farm waste under, and allow it to rot. This is fine, but it produces only modest improvements in soil fertility, and they are largely temporary. But as we shall see later in this essay, soil carbonization by small farmers should now be practical, because I have developed a charcoal furnace specifically designed to carbonize farm waste - in a device that is cheap and easy to build, and almost a hundred percent efficient, as well as easy to use. Details are below.

Saving The Planet

If practiced on a truly large scale, the carbonization of soil in the tropics and subtropics can not only solve, but might even reverse the problem of global warming.

That is quite a sweeping statement, but it is true, as we will see. To understand how this is possible, you need first to understand the biospheric carbon cycle.

This is a very simplified version, so please, if you are a scientist or other academic, don't write me to correct the details. The intent of the following explanation is only to outline the carbon cycle in its very broadest dimensions, so that non-technical readers can understand my explanation of why soil carbonization could have a major, beneficial impact on global warming.

The carbon cycle begins with atmospheric carbon dioxide, the greenhouse gas we all know and are growing to hate. It is a natural part of the atmosphere, however, and prior to the widescale use of fossil fuel in industry, the concentration of carbon dioxide in the atmosphere was roughly 260 parts per million by volume. Digging up carbon-based fuels out of the ground and burning them, adds to atmospheric carbon dioxide, since carbon dioxide and water vapor are the primary combustion products of burning fossil fuels. A century and a half of burning (oxidizing) fossil fuels, most of which consists of carbon, has raised the concentration of carbon dioxide in our atmosphere to roughly 360 parts per million. We are burning fossil fuels at such a rate that this value is increasing at roughly 10 parts per million per year. This does not sound like a lot, but carbon dioxide is extremely efficient at trapping heat in the atmosphere, and that is why its influence is all out of proportion to its concentration, and that is why increasing its concentration even a little bit matters a whole lot.

As you may recall from your high-school science classes, plants breathe in this carbon dioxide (which is all the same, regardless of whether it is natural in origin or comes from human activity), and through photosynthesis, combine it with water and turn it into the carbohydrates that make up the plant - the sugars, cellulose, lignin and other materials. When the plant dies, this carbon, which was sequestered (locked up) temporarily in the plant's tissue, is oxidized by decay organisms and is released back into the atmosphere in the form of carbon dioxide. The cycle is complete - the carbon dioxide becomes available for another plant to absorb. The theory of planting trees to slow global warming is that trees sequester this carbon in their plant tissues - wood - for centuries. But of course, they eventually will all die and rot away, and so the carbon dioxide they are supposed to sequester will eventually be released back into the atmosphere anyway. Other schemes have been suggested for sequestering carbon dioxide - usually by liquifying carbon dioxide and dumping it on the ocean floor (with unknown and unpredictable consequences for ocean ecology) or pumping it into abandoned natural-gas wells (again with unknown and unpredictable ecological consequences). But all these schemes are expensive and produce no economically useful outputs, so implementing them is problematic at best - it would have to be done by a government program, because there is no economic incentive for the private sector to do it.

There is another way to sequester the carbon and one that does indeed have a private-sector incentive associated with it. Charcoal consists almost entirely of carbon - by weight, carbon makes up between about 70 and 98 percent of charcoal. And charcoal is chemically stable - it does not react readily with either water or atmospheric oxygen at ordinary temperatures, so once it is well mixed into the soil, it will remain there for geological time scales. Indeed, scientists routinely find charcoal from forest fires in sediments laid down during the age of the dinosaurs and before. So once added to soil, carbon in the form of charcoal will remain there until it is physically separated out or oxidized in the interior of the earth. This process of geological consumption simply does not happen on any kind of time scale with which we need to concern ourselves. Charcoal is also easy to make - simply heat up any solid biological product to a temperature of about 470 degrees Farenheit, and volatile organic compounds come off as smoke, leaving behind charcoal. The carbon atoms simply reattach themselves to each other, and what we have left is elemental carbon - in the form of charcoal. And as we have seen, if farmers knew what it could do for them, they would have a major financial incentive to create charcoal from their farm wastes and add it to their soil, sequestering it not for decades or even centuries, but effectively permanently.

So how can this possibly have a measurable effect on the atmosphere? After all, the atmosphere of this planet is really big - a hundred miles deep and covering millions and millions of square miles of surface area. Even at the small fraction of the atmosphere that is carbon dioxide, that amounts to a truly staggering amount of carbon that we are swimming in - billions of tons. How could a bunch of farmers, carbonizing their farm waste and plowing the charcoal under, possibly have that much of an effect? The answer is numbers. Millions of farmers, all doing this together, could have an enormous impact, bringing atmospheric carbon dioxide right back to its pre-industrial levels. Here are the back-of-the-envelope calculations that show how this is plausible and even feasible:

The weight of all the air above the earth's surface amounts to 14.7 pounds per square inch at sea level - that is the same as atmospheric pressure. This means that every square inch of earth's surface (at sea level anyway), has 14.7 pounds of air resting on it. For the sake of convenience of understanding what is happening and visualizing that in our minds, let's convert that to weight per square foot. There are 144 square inches in a square foot, so that means that the weight of the earth's atmosphere at sea level is 2116.8 pounds, or a little over a ton per square foot (we don't feel that pressure, because we are immersed in the air, which presses up as well as down, and from the inside as well as the outside on us, cancelling out the pressure). We know that the volume of that air is composed of carbon dioxide to the extent of about 360 parts per million, but since carbon dioxide weighs more than air, for the purposes of these calculationswe need to convert that composition by volume to a corresponding composition by weight. It turns out that at equal temperature and pressure, carbon dioxide is 54% heavier than air, so if we multiply our 360 parts per million by 1.54, it turns out that the composition of the atmosphere is currently 556 parts per million carbon dioxide by weight. It follows then, that of the 2116.8 pounds that the atmosphere weighs per square foot on the earth's surface at sea level, 556 parts per million of that weight is carbon dioxide. Divide the 2116.8 by a million and multiply the result by 556, and you will have the weight of the carbon dioxide only, per square foot, that is bearing down on the earth's surface. The result is 1.17 pounds. But carbon dioxide includes a lot of oxygen, and if we want to know how much charcoal that would represent, we need to get rid of the oxygen in the carbon dioxide. Well, it turns out that 37% of the weight, roughly, of carbon dioxide is actually carbon (the rest is the oxygen), so we need to multiply the 1.17 pounds by 37% to get the weight of the carbon only. Turns out to be 0.43 pounds, or 6.92 ounces. If you turned all the carbon dioxide in a column of air of one foot square and as high as the top of the atmosphere into carbon (or charcoal), that is what the resulting carbon would weigh - 6.92 ounces.

Obviously, since atmospheric carbon dioxide is a vital, even critical part of our biosphere, we don't want to get rid of it all. We want only to get rid of the part that mankind has added to the atmosphere since the Industrial Revolution began. So if we calculate what percentage of current atmospheric carbon dioxide has been added by man, the percentage works out to 44%. So of our 6.92 ounces per square foot, the Industrial Revolution is guilty of adding a hair over 3 ounces per square foot.

The rub here is that farmers, to have a significant impact on global warming by adding charcoal to their soil, will have to add this amount for all the planet's surface area, land and ocean alike, not just the area of the planet's surface under cultivation. So we need to know how much of the planet's surface area is under cultivation in tropical and subtropical areas to determine how much they would need to add to save our skins. Turns out, according to United Nations Food and Agriculture Organization and from other sources, that pretty close to 1.6 percent of the surface area of the planet is given over to agriculture in tropical and subtropical regions. To reset the composition of the atmosphere to pre-industrial levels, the farmers in those regions are going to have to add to their soil, charcoal equal to three ounces divided by 1.6% - or in other words, 190 ounces per square foot of cultivated area.

This amounts to 11.8 pounds of charcoal per square foot of cultivated area. Depending on the density of the charcoal and the density of the soil, this is roughly the amount needed to get the optimum 30% by volume to a depth of about three feet. Just perfect! Just what the farmers need to do! And just what the planet needs to give us a second chance! So if every farmer in the tropics and subtropics got on the ball with this program, we could completely undo all the damage that we have done to our atmosphere with our fossil fuel addiction and put things right.

As it turns out, we need not rely just on tropical farmers, who stand to benefit the most from this soil carbonization. Recent work by Cornell University has shown that agriculture in temperate and even subarctic regions can benefit from soil carbonization as well. In the temperate agricultural zones, soil carbonization can greatly assist in improving soil texture as well as considerably improving a soil's fertilizer absorption and retention - making application of fertilizers far less frequently necessary. Since this is one of a temperate-zone farmer's largest costs, it can be of great benefit to a temperate-zone farmer seeking to improve his profitability. Since temperate-zone farmers can benefit too, if even a third of the world's farmers were to carbonize their soils, the entire problem of anthropogenic global warming would simply go away. Finally, a few people are beginning to recognize this in the academic community, and new proposals are coming out to include soil carbonization as a scheme to be subsidized under the Kyoto Protocol.

Getting The Job Done

It strikes me that getting this job done should be politically feasible. Everyone involved should be all for it - it gives conservatives a graceful way out of their denial, it gives liberals a project that does not involve government forcing people to do what they do not want to do, it gives farmers and gardeners around the world a strong economic incentive to sequester and bury huge amounts of carbon over long periods of time, and it gives industry an incentive to help make it a reality, by creating a means, through the Kyoto Protocol, of ridding itself of a troublesome pollutant in a cheap but an environmentally beneficial manner.

So here is how I propose to make this happen. First, the big environmental NGO's need to get on board. They need to see what is at stake here, and how this could be a huge boon to the environment. They need to get to work throughout agricultural regions of the world, providing the tools and knowledge, and showing the farmers how they can benefit from this discovery.

Second, governments can get involved by offering Kyoto-Protocol carbon tax credits to farmers. Since it is the farmers who would be doing the sequestration, they should be the ones to benefit under Kyoto - and it gives them further incentives to participate, besides the improved productivity of their soils. It can be another income stream for the farmers if the governments set up the programs in the proper way.

Third, industry can benefit by building the charcoal furnace equipment I will describe below, and unrelated industries should benefit by finding themselves under less pressure to change products and processes to curtail carbon dioxide emissions, and a new industry - agricultural soil carbonization - could be established. This should give industry, particularly the fossil fuel industry, an incentive to help encourage soil carbonization by third-world agriculture, so industry can go on doing what it is doing now.

Forth, where large-scale family farming and industrial-scale farming is already well established, I foresee large companies getting into the soil carbonization business, because farmers simply can't create enough charcoal to meet their needs - it just isn't practical over a reasonable timeframe. So bringing in someone else to do the job makes a lot of sense. The broad details of the business plan of such a company would work something like this - the soil carbonizing business would own farms where kenaf, bamboo, switchgrass and other high-biomass crops are grown as a feedstock, or be located near sugar cane crushing mills, where large amounts of baguase (crushed cane fiber from which the juice has been extracted) is available cheap or for free as a feedstock for the charcoal production process. The company would have large scale charcoal furnaces, a scaled up version of what I will describe below, with which they will produce charcoal powder on a grand scale. The company would approach landowners with a proposition - it will finance the carbonization of all the farm's cultivated soil through a lein, and the farmer can pay back the lein through the improved crop yields over a period of several years - the farmer pays only for increased yields, and for only a set number of years. This is the guarantee of results to the farmer - if there is no increase in yields, there is no cost to the farmer. Once the lien is satisfied, additional profits resulting from increased productivity, from then on, are the farmer's. If the farmers stand to lose their farms anyway from the lack of productivity and high operating costs they already face, and can see the results on neighbor's farms, few would refuse.

In Africa, South Asia and other areas where subsistence farming is the norm, I anticipate that it would be the NGO's and government programs that would provide the means and incentives, the details of which would have to vary from region to region. Governments would provide the charcoal furnaces (financed through foreign aid, most probably), the NGO's the know-how, and the farmers would do the work. They would concievably have a single small-scale carbon furnace, providing charcoal from their field waste for use in domestic cooking use as well as the carbonization of the soil on the farm. Once the farm's soil is adequately carbonized, the farmer could sell his furnace to a neighbor, or use it to produce charcoal for briquette manufacture - an additional income source. This could be a key part of anti-poverty programs in the third world, because it can help a smallholder greatly improve the productivity of his limited resources, while giving the government an incentive under Kyoto to help him out.

A Cheap, Easy-To-Use And Efficient Charcoal Furnace

When I began researching for this essay, I quickly discovered to my dismay that the technology for producing charcoal has not changed much, literally, in centuries. It is still done, for the most part, the way it always has been done.

It was obvious to me that if I were to persuade large number of people to start producing charcoal, and on a large scale, that I had to come up with a more convenient, faster, more efficient and less messy way of doing it. So I started thinking about how it could be done in the manner needed. I thought about it for some time, and finally, in a flash of inspiration, the answer came to me.

A tubular furnace, using an ordinary piece of large diameter iron pipe, heated by a solar energy reflector, would be the answer. Not dependent on its own output as a heat source, any solid organic material feedstock could be used - even wet leaves - and the product would take minutes to produce, rather than hours or even days as is needed for the usual methods. And virtually all the charcoal produced would be available as product, since none is consumed to provide the heat for the process. Push the raw, even wet feedstock in one end, and minutes later, finished charcoal comes out the other. What could be simpler or easier?

So on consideration, the design worked out to something like this - a piece of pipe, blackened on the outside to facilitate the absorption of the heat, about three or four inches inside diameter, and about ten to fifteen feet long, is suspended over a trough reflector, shaped into a parabola in cross-section, with the pipe suspended at the focal point, parallel to the length of the trough. The trough would be about eight to ten feet wide, and is lined on the inside with the solar reflectorizing material, which is nothing more than shiny metal - in a pinch, aluminum foil, shiny side up, could be simply glued to ordinary sheet metal to provide the shiny surface (the shiny aluminum surface could be sprayed with clear acrylic to preserve the shine). The resulting device is mounted with the length on an exact east-west line. If this is done, the only adjustments that need to be made to keep the furnace operating at peak efficiency is to keep the reflector tilted to the current seasonal sun angle. No hourly or daily adjustments need be made. Simply push the feedstock in one end, and if it gets heated to more than 470 degrees during its transit through the pipe, out the other end comes low temperature charcoal, ideal for soil carbonization. Easy as that.

For a third-world farmer without access to electricity, the furnace would be pretty much as described, with the feedstock being loaded from a small bin-like arrangement welded to one end of the furnace pipe. Feedstock would be pushed into the furnace pipe with tool consisting of a small pipe as long as the furnace pipe, on which a disk is mounted on the end, a disk somewhat smaller than the inside diameter of the furnace pipe. The disk's purpose is simply to force the feedstock into the pipe and through it, and clear blockages as needed. As feedstock enters one end of the pipe, the finished charcoal is simply pushed out the other. Gasses driven off by the heating exit through the feedstock end - the other end is left completely blocked by charcoal, which precludes the entry of oxygen and thereby keeps the efficiency high.

There are endless variations on this theme that are possible. For industrial furnaces, the farmer's feedstock tool could be replaced by an auger screw. A gearmotor, switched by a thermal switch, would come on when the sensor detected that the temperature of the furnace pipe exceeded the setpoint, turning the screw and loading the feedstock from the bin and carrying it to the far end of the pipe. It would run until the sun went down or behind a cloud, and the temperature dropped below the setpoint. Loading of the intake bin could be done automatically, too, with another auger screw or a conveyor belt, which could load several furnaces at a time. Output could drop into a hopper emptied by yet another auger screw.

Another variation would be to collect the outgassing products - smoke - which on a large scale, would be worth doing, as the condensate could be processed into useful petroleum substitutes including lightweight tars readily convertible to diesel fuel, or burned on cloudy days to provide the heat necessary to keep the production going. This would also improve environmental performance by reducing the air pollution that would result from releasing the smoke into the air.

My Personal Experiments

Being an indoor gardening enthusiast, I decided to do some experimenting with soil carbonization myself, and have been doing these experiments for enough time now, that I feel I can offer some useful results.

My first effort was using the standard formula for terra preta: one third loamy soil, one third compost and one third charcoal powder and granules. My garden loam was simply dug up from behind the house. The soil where I live here in Costa Rica is very heavily weathered tropical clay, however, so I added a great deal of sand to improve the texture and make it more like a loamy soil. I then obtained some well-composted ox manure from a neighbor who keeps several oxen, to use for the compost component. And the charcoal powder came from another neighbor who makes charcoal commercially for barbecuing.

The charcoal had a great deal of ash in it, and to avoid burning the roots, I washed the charcoal in a cloth bag several times until the rinse water ran clear. The mixture components were mixed together in the proportions given above in a five-gallon bucket, and the mixture was moistened and allowed to set for about two weeks to allow the bacterial community to stabilize.

Once it had stabilized (as evidenced by a stable, healthy, earthy smell replacing the burnt smell of the charcoal), I then planted quite a few African violets from my collection in the resulting mixture. The plants did not exhibit any evidence of transplant shock, so I was hopeful that they would take off and grow rapidly. And after a period of about two to three weeks, new growth became evident. The resulting plants have been growing magnificently, and blooming constantly and profusely since I planted them in this mixture, but I have noted, however, that it took quite some time for the new growth to really take off - about two months, in fact. Having kept the remnant of that same mixture in the same bucket and keeping it moist, I quickly discovered that the dramatic growth I was hoping for was quickly realized when new plants are planted in this well-aged mixture. Allowing the terra preta to condition itself for a few months appears to be key to using it as an optimum potting mix for houseplants. Not sure why, but I suspect that it is getting the right bacterial community established and stabilized. I have had excellent results with potted philodendrons, orchids and maidenhair ferns as well.

Some time ago, I ran across a reference in Science Daily about the use of coffee grounds for garden compost. It had mentioned that coffee grounds are a rich nitrogen source - about 2% by weight. It occurred to me that if they were pyrolized, the resulting charcoal would be about 4-5% nitrogen by weight, and that would make them a very good source of organic nitrogen for my African violets, which are very sensitive to chemical fertilizers and burn very easily, but which need nitrogen in abundance. So I came up with a simple stove-top pyrolizer design that would enable me to test this idea. The pyrolizer described below will only work on a gas stove - don't attempt to try it on an electric stove. It won't work and will only succeed in filling the house with smoke!

If you try this, be aware that this process will produce a great deal of heat; much more than the stove burner itself. This is desirable; it helps the pyrolizing process run efficiently. So it is vitally important that to prevent a fire, you must ensure that there is nothing for at least three feet (a meter) above the stove, or within a foot and a half (50 cm) of the burner that can be damaged by heat or could be a source of ignition. Flame may, and probably will emerge from the apparatus and so it must be accomodated with plenty of room! Smoke hoods must be cleaned in advance of any grease present, or it will melt and could drip onto the apparatus, causing a fire! Monitor the process closely to ensure safety, and shut off the gas at any hint of trouble! Do this at your own risk, and keep a fire extinguisher handy!

The pyrolizer consists of two old metal paint cans, the first a one-quart can with a lid, and the second, a one-gallon can without a lid. Both are first burned in a fire to remove remaining paint and painted labels. In the lid of the one-quart can, I punched a few holes (four or five) in the center of the lid with a nail and a hammer. This is to allow the volatile gases resulting from the pyrolizaton process to escape. The one-gallon can will be used as a chimney to keep the heat as close as possible to the smaller can containing the material being pyrolized and speed the process. It is modified by making a small hole in the bottom with a cross of two slits, each about an inch (2.5 cm) long, creating four flaps which can be peeled back to adjust the draft during the pyrolizing process.

The used coffee grounds, thoroughly air dried, are then tightly packed into this one-quart can, and the lid with the holes in its center is then tightly replaced. The paint can with lid in place is then placed upside down, on one of the large front natural gas burners on the stove, centered as carefully over it as possible. The large coffee can is then also placed upside down over the smaller one, also carefully centered, with the flaps bent back about half way. They may need adjustment as the process proceeds, and that can be done with a couple of screwdrivers, one to hold the can down while the other one is used to bend the flaps up or down as needed.

The burner is then lighted, and turned up to full output. After about three or four minutes, a change in the flame color will be noted - the flame will change to an orange color. This indicates that the pyrolization has begun. After about ten minutes, the process will reach its maximum speed, and the burner flame will be almost entirely orange, as it is now burning the volatile gases (a.k.a. smoke) coming out of the nail holes in the lid. If the orange color is predominantly on one side, it means that the pyrolizer is not centered on the burner and should be adjusted slightly by poking it a bit with a screwdriver in the direction of the blue part of the flame. If flames are escaping from around the outside of the large paint can, it means that the draft is inadequate, and the flaps need to be bent back, opening the hole a bit. The hole should be opened only enough to keep the flame from escaping outside the large paint can. Depending on how fast the process is running, flames may actually emerge from the hole in the large can.

The process will typically take up to about four hours, depending on how tightly the grounds were packed into the inner can, and the heat output of the burner. You will know that the pyrolization process is fully complete when the burner flame has completely and with stability, resumed its normal blue color. When this happens, turn the burner off and allow the apparatus to cool for at least an hour. It will retain heat for a long time in the center of the pyrolized grounds, so use caution when inspecting the results.

As a potting mix for African violets and tuberous begonias, I have tried a mixture of 50% pyrolized coffee grounds and 50% composted ox manure. The resulting mixture has ideal texture and moisture retention characteristics when packed a bit into the pot. I condition this mixture by moistening it, and putting it into an airtight container for about two weeks, to kill off any bugs growing in the compost, and then allowing it to air out until it resumes its healthy earthy smell - that should take about a week. Using this mixture, I have found that the pyrolized coffee grounds are far superior to the ordinary charcoal for potting my African violets and have also found that tuberous begonias (grown here as houseplants) also do exceptionally well in this mix - in fact, cuttings taken from the latter will very quickly root out and continue growing as if nothing ever happened! The African violets also do exceptionally well - exhibiting immediate, rapid growth and profuse, stable flowering. Leaves of African violets can be rooted in this mixture directly, without going through the process of rooting them in a cup of water first. I have concluded that the pyrolized coffee grounds are well worth the effort, as the results with every mix I have tried have proven to be spectacularly successful. Everyone who sees them remarks that they have never seen African violets blooming so profusely, and this blooming is continuous, only slowing down a bit from time to time. They never seem to stop to rest.


The obscure discovery made by archaeologists and soil geologists working in the Amazon basin a few years ago could have huge repercussions - while it saves millions of farmers in the tropics and subtropics from lives of poverty and destitution, it could also save the world, literally, from the folly of modern man by learning from the discovery of those long-dead aboriginals who made the original discovery all those centuries ago.

The only question that remains is whether we will apply the lesson in time. The tools are there; we have the knowledge and technology to get the job done. We have the incentives to do it. We have the urgent need to get on with the task. Let us not be ignoring what we need to do, and can do. Not only can we better feed ourselves and help millions overcome poverty in the process, but even more importantly, we can save our very home, the only one we have, from the mess we have made of it. There is hope for the planet after all. But we had better get busy.

Update - 8-20-07:

The work at Cornell and other universities has attracted enough attention that soil chemists, agricultural experts and even politicians are finally beginning to recognize the significance of this discovery.

As of this writing, at least one conference (in Australia) on "agrichar" as soil carbonization has come to be called, has been held, drawing interest from all over the world. It was presented by the newly-organized International Agrichar Institute.

Several startup companies, such as Dynamotive Energy Systems in Vancouver, B.C. have appeared, beginning research in large scale pyrolization of farm waste, with a view not only to creating charcoal for soil carbonization, but also for the "bio-oil" that is the smoke condensate - itself a product of sufficient value to justify the project. In fact, it has been calculated that the smoke condensate alone from a square mile's worth of corn stover can generate enough fuel to power 330 automobiles - and in this day and age of high gasoline costs, that's attractive to big business. Since 30-50 percent of the carbon in the feedstock goes up in smoke, capturing and condensing that smoke as a bio-oil makes a great deal of economic, as well as environmental sense.

This has attracted attention from politicians, too. Senator Ken Salazar (D-Colo.) is drafting legislation to be included in the upcoming farm bill to encourage the tillage of pyrolized farm waste. Experiments are being done to look at the pyrolization of manure and sewage sludge, to see if they can help create terra preta when added to farm soil.

It has been discovered that permanent soil fertility enhancement by using charcoal amendments alone in temperate-zone soils is achieved only through good soil management. The dramatic and permanent improvements seen in terra preta is probably achieved only by colonization of the soil by highly specialized micro-organisms, and this may take decades or centuries to achieve in temperate zone areas. But even in the absence of this terra preta effect, the immediate improvement in the ability of the soil to absorb and retain fertilizers is more than worth the trouble of adding the char. And someday, after decades of good soil management, the temperate-zone farmer may be able to wean himself off of fertilizer altogether as his soil becomes true terra preta.

Update II - 4-22-13:

A new study has discovered that most carbon that is added to the soil naturally through fires, crop-residue burning, etc., is lost through rainwater runoff to streams and rivers, where it becomes dissolved in the stream water and ends up in the ocean. For this reason, the new recommendation is that extra care should be taken to bury the charcoal as deeply as possible - at least several inches from the soil surface - and use various techniques to minimize surface water runoff - especially to avoid excessive irrigation. This will ensure that added charcoal remains in the soil to do its magic.

Also, new research at Cornell and elsewhere has indicated that biochar that was pyrolized at high temperatures is more effective in most soils than is low temperature biochar, because the reduction in hydrophobic hydrocarbons (oils and resins) means that water can more easily wet the particles, making dissolved ions more readily available for adsorption.

Internet Resources:

Scientific American has put up a special 3-part report on terra preta on its web site. It discusses current research results, political efforts to promote terra preta, and the potential impact on global warming. An excellent read!

Here is a very comprehensive list of internet resources, companies and organizations involved in soil carbonization.

The newly-formed International Agrichar Institute has a web page with useful resources, including notes from the 2006 meeting of the American Association for the Advancement of Science, where terra preta was discussed.

A good overview of what is currently being done in terra preta research and applications has been the subject of a recent symposium at the University of Georgia.

The "Terra Preta Homepage."

Cornell University is pioneering some research in terra preta, and has an extensive web page describing their activities.

A recent press release from Cornell University describes how soil carbonization could be incentivized under the Kyoto Protocol, and how it has the potential to greatly reduce the effects of greenhouse gas emissions.

An interesting article in the prestigious science journal, Nature. It discusses some of the obstacles on the road to adopting terra preta as a solution to both soil fertility problems and the global warming crisis.

Virtually any organic matter (that is free of toxic heavy metals) can be pyrolized to char and used for the creation of terra preta. New work being done at Virginia Tech is focused on the use of chicken litter as a pyrolization feedstock - and they have found that as much as half of the carbon in the feedstock can be captured as bio-oil in the condensed smoke, thereby paying for the costs of pyrolization, and leaving an ash-rich char as a byproduct - ideal for the formation of terra preta.

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