Field Biochar Manufacture

This posting by A. Karve at the terra preta/biochar forum brings fresh practical insight to the task of producing biochar in the field. As noted I have posted on an earthen kiln protocol that can be used by farmers without access to metal. This posting allows me to refine my thinking for the modern subsistence farmer and even well beyond that level.

Start with no more than a steel drum whose top and bottom has been removed. Place a layer of inch thick branches down as a packed floor for the kiln. Place the kiln end up on to this floor. Air will be able to pass under the edge of the drum through the packed branches at a moderate speed.

Pack the drum with chipped wood or chopped biomass. Do not create tight layering that could cut of air flow entirely. Yet get the packing level up to fifty percent. Once the drum is filled, place a charge of dry wood to act as a starter on top of this load. You may already place six inches of soil around the edge to reduce the center diameter to a quarter of the total. Fire it and let the fire burn most of the wood layer in order to be fully engaged.

At this point smother the top of the fire by throwing six inches of dirt over the center. Or alternately, place a metal lid with a six inch chimney pipe with a damper for fine control.

What we have done here is very familiar to those of us who experienced the methods of the nineteenth century. We have actually banked the fire. The surface cannot flare up losing both heat and fuel and only a limited amount of fuel is burning at any one time and it is mostly in the form of the volatiles in the early going.

Over several hours, the burn front will migrate down to the ground and burn out the floor of this kiln, allowing the edge of the kiln to connect to the earth, and cutting off the air flow eventually. In practice, I consider this to be more of a fail safe to prevent a total burn out of the fuel charge as eventually happens in a banked stove.

I like the dirt layer idea, with or without a metal lid. It acts like a filter for the escaping gases and likely maximizes their combustion. In addition, it will end up been blended with the end product to produce a dry easy to handle mixture if the fire is not quenched with water which is likely necessary.

I suspect that it will simply be better practice to water the fire before it fully engages the floor. Once that point is reached we are very close to running out of volatiles and the charcoal then becomes the primary fuel.

Thus, in lieu of naturally packable materials such as corn stover and bagasse able to produce an earthen kiln, we have a simple metal kiln design that is easily expandable and able to work on the modern farm. There a square set metallic box can be set up in the same manner and material loaded in and packed. This is all rough and ready and certainly will not achieve the optimal thirty percent yield, but it will produce twenty percent or better quite handily.

The key idea is to have the bottom edge set on a layer of branches or any other material able to sustain a fifty percent air flow in through the bottom. The top layer of dirt might be dispensed with if a holding layer does not exist. The Indians had palm fronds to work with. A metal sheet with a chimney closing it all off will do the rest.

My most important point is that this is easy to assemble in some form or the other anywhere and regardless of the local economy. Old rusty galvanized sheet steel is very suitable. You may even get away with using rope on the outside to hold it together. After all the core temperature will be mostly in the core and still be around 300 to 400 degrees. Hot spots on the wall will need an unusual source of air and that really means a fully engaged fire. If that is happening, you have plenty of other problems and it is not working at all.

Dear Martin,

I really do not know, how much char is to be applied per hectar. But I can tell you how to make char out of your burnable organic waste. The simplest device is a top-lit updraft kiln. It consists of a vertical cylinder, having relatively small holes near its base for primary air. You fill the cylindrical body of the kiln with the material to be charred and then light it from the top. Once the fire gets going, you place a lid on the cylinder. There is a chimney built into the lid. The lid does not sit flush on the kiln, but there is a gap between the lid and the kiln. The draft created by the chimney sucks secondary air into the chimney, where it gets mixed with the pyrolysis gas to burn it. The biomass burns downwards, leaving a layer of charcoal on top. As the primary air comes upwards, it meets the burning front which traverses downwards. The burning biomass utilises all the oxygen in the primary air, so that the air going up through the layer of char has only carbon dioxide, carbon monoxide, nitrogen and the pyrolysis gas left in it. As there is no oxygen left in the updraft air, it cannot burn the char that has formed above the burning biomass.The pyrolysis gas and carbon monoxide burn in the chimney, because of the secondary air that is sucked in through the gap between the chimney and the kiln. You have to find out by trial and error, how long it takes to char the material loaded in the kiln. After that much time is over, you remove the lid, and extinguish the fire by sprinkling water over the burning material. This particular device is portable and manually operated. There are larger charring kilns, based on the oven and retort process. Prof. Yuri Yudkevich, a Russian scientist, has made them for charring useless material generated by the timber industry in Russia. We are already using both types of kilns under field conditions in India for charring agricultural waste as also urban waste. We have a video CD that describes the kilns and you can fabricate them by watching the video CD. I have not used Prof. Antal's kiln and have absolutely no idea how it operates. Our web site www.arti-india. org would show you how to get our CDs by paying us through Pay Pal.

Biochar in the Garden

Phillip small is developing this FAQ on the application of biochar to the home garden. Although a work in progress, as it must be with the current state of knowledge, It covers enough to give a new user a running start.

The evidence to date supports spending a fair amount of effort to produce a finely powdered product. In fact I would get the appropriate screen and simply use only the fines in the garden. This of course will prove a little difficulty with commercial wood charcoal were the fines have already been cleaned out.

Everyone is discovering that crushing wood charcoal is not easy or convenient.

If one actually has an efficient retort working on a pyrolysis gas fuel system, then we have the option of using non wood plant material as a feed stock which immediately solves the problem. The pollen evidence and the additional likelihood that the original terra preta was cooked up in earthen kilns formed out of corn stalks and their root pads informs us that the original biochar protocol did exactly this.

In the meantime, crushing wood charcoal is the available option. Laying down a ground sheet to capture the charcoal powder on a concrete slab, then a layer of charcoal and then a plywood sheet, creates a crush zone. Driving your car back and forth over the sheet may do some good. Making use of a drop weight while standing on the panel is the next option we may want to try.

What you will learn is that as fineness goes up, so does energy expenditure at a much faster rate. Welcome to the world of mining and milling.

The reason this all works is because the surface of elemental carbon grabs and holds nutrients until a root cell arrives with its biological entourage and extracts the nutrient away from the carbon. The nutrient so bound can not escape into the mobile drainage system. Obviously a root will have difficulty penetrating a large chunk of charcoal.

As yet no one is marketing powdered charcoal as such, although that can not be far off. That will be followed very quickly with fertilizer blending. In the meantime it is pure do-it-yourself.

In terms of application, I would blend five pounds of powder in ten to twenty pounds of soil with fertilizer and use that to set seeds in mini hills of the blend. That way you are not treating the huge amount of area that lies in between the seed beds.

This should maximize immediate results for the home gardener.

I would particularly like to see this tested in this manner on the clearly poorer soils. Fine loamy soils barely need the assistance. Former desert soils most certainly do. And there are plenty of urban lots in which removed topsoil was never properly restored. At least with this protocol, the home owner has a method for soil restoration that compliments and supports any thing else he may try.

A really interesting experiment would be to plant alfalfa in a very thin top dressing that included fifteen percent biochar on a subsoil base. It is the nature of alfalfa to run a root system both deep and broad while also fixing nitrogen. This penetrates the sub soil with organic material on an ongoing basis. The top dressing holds the soluble nutrients also needed. The question that we are really asking here is whether this protocol is able to produce a viable top soil quickly. While this is going on, it may be possible to harvest the alfalfa and perhaps aerate the top three inches. Obviously any now barren non productive field could be used for this experiment and I expect the carbon to counter even salinity by sequestering the salts into the carbon.

The important point is that the initial top dressing does not need to be very thick, although more will be clearly better. But if you have an impossible soil, getting anything to set up and establish itself is a blessing. The established root material will then start the process of rehabilitating the soil. After that it is a matter of how much of a hurry you are in. An established alfalfa field providing a steady and improving supply of fodder is at least nicely carrying itself.

Welcome to a Gardening with Biochar FAQ!

... a work in progress...

When gardeners add biochar to garden soil, we are, in effect attempting to follow in the footsteps of the originators of Terra Preta. Because we don't know exactly how that process worked, nor how we can best adapt it outside its area of origin, we are left to discover much of this by experimenting with our own gardens and comparing observations within our own communities.

1.0 What is Biochar?

Biochar is charcoal formed by low temperature pyrolysis. Medium temperature pyrolysis produces a more traditional charcoal, high temperature pyrolysis produces activated charcoal. Ideally biochar is made in a way that achieves maximal woodgas condensate retention.

1.01 How does biochar relate to agrichar and to Terra Preta?

Agrichar is a synonym for biochar. This material was fundamental to the creation of Terra Preta de Indio, as it is to creating its modern equivalent, Terra Preta Nova. Terra Preta "Classic" was made by adding charcoal, broken pottery shards along with the organic fertilizer amendments. This, in conjunction with the microbial ecology occurring in these soils, resulted in an incredibly fertile soil, and a reputation for self-regeneration.

1.02 What is pyrolysis?

Pyrolysis is a chemical decomposition of organic materials by heating in the absence of oxygen. This releases heat energy and yields combustable gases (aka syngas, wood gas, and producer gas) and charcoal. The charcoal produced is a combination of black carbon, along with small amounts of woodgas condensate and ash.

1.03 What temperature range is considered "low temperature" in the context of biochar?

The theoretical low end of the range approaches 120 deg C, the lowest temperature at which wood will char, (Reference) thus the temperature at the pyrolysis front. A more practical low end is to use the piloted ignition temperature of wood, typically 350 deg C. (Reference) The theoretical high end, between biochar and more traditional charcoal, depends on the process and feedstock used, but is seldom indicated in excess of 600 deg C.

1.04 Can I substitute other forms of charcoal for biochar?

Yes, up to a point. The woodgas condensates in biochar give it considerable value, but that is not to imply that using simple charcoal, or charcoal made from other than plant materials, won't produce some, and even most, of the same benefits. It is normally adviseable to avoid charcoal briquetttes because the binders used during manufacture can add undesireable constituents.

1.05 Why are the condensates valuable?

We believe this to be the case because higher temperature charcoal does not produce as much of an observed beneficial effect.

1.06 Is biochar made from hardwood best?

Biochar made from hardwood is richer in condensates when compared to biochar made from softer wood, from bamboo and from less woody vegetation. The fact that hardwoods were readily available to the originators of Terra Preta de Indio has not escaped the attention of Terra Preta enthusiasts.

1.07 Where can I join in with this community of Terra Preta enthusiasts?

1. Bioenergy lists: Terra Preta: the intentional use of charcoal in soils.
2. Bioenergy lists: Terrapreta -- Discussion of terra preta, the intentional placement of charcoal in soil.
3. Hypography Science Forums: Terra Preta

2.0 How do I Get Biochar?

You can purchase biochar, purchase a charcoal substitute, or you can make it yourself.

2.01 Where can I purchase biochar?

Currently manufactured biochar is in short supply and is needed for research projects. The alternative is to purchase charcoal and use it as a biochar substitute. Cowboy brand hardwood charcoal is available in the United States in 20 pound bags by the pallet, about 600 pounds, for less than US $ 0.7/lb. For larger amounts, as in a shipping container, consider coconut shell charcoal, available for less than US $ 300/mt. Worth repeating: It is normally advisable to avoid charcoal briquettes because the binders used during manufacture can add undesirable constituents.

2.02 How do I make biochar?

While colliers the world over normally use either a covered pit or a covered mound (earth kiln) to make charcoal, most gardeners will want to start with an easier method that works at a smaller scale. Home pyrolysis is pretty easy to accomplish and a bottom lit burn barrel is the common starting point. Make sure the openings at the base of the barrel are large enough. Light it off, give it an occasional shake to settle the fuel, and, when done, pop a cover on it or douse it with water. The burn in all of these approaches can produce a fair amount of smoke and partially combusted gases. Out of concern for air quality, many gardeners may prefer not to use these approaches.

2.03 What are some less smokey approaches to making biochar for the gardener?

Choose your feedstock wisely. No matter what technique you use to make charcoal, choosing uniformly sized, dry woody material produces the highest yields. Uniformity is one reason that colliers will routinely use coppiced hardwoods.

Inverted Downdraft Gassification. For a cleaner burning configuration, consider a Top Lit Updraft (TLUD) technique, also referred to as an inverted downdraft gassification. The technique looks simple but in reality it involves some fairly sophisticated physics (PDF). That doesn't prevent success using common materials and dead simple design. Take that same open barrel configuration, tweak the design per the afformentioned physics involved, and now light it from the top instead of the bottom. This takes a different skill set than lighting from the bottom but its also not that difficult to master. A little vaseline or ethanol on a cotton ball can work wonders for starting up. Once the fire gets going, the top layer of wood burns, creating charcoal, naturally. The heat from the charcoal layer burning heats the wood below it, and ignites it, but at a lower temperature sufficient for pyrolysis. The gases released by pyrolysis (carbon dioxide and water) flow through the charcoal layer. Glowingly hot charcoal has a wonderous ability to strip oxygen molecules from of anything that passes over it, so it converts the water into hydrogen, and the carbon dioxide into carbon monoxide. These two gases are flammable and they are ignited once mixed with air coming into the top of the open barrel above the charcoal layer. The result is a scrubbed gas-fed flame that is much more controlled, and which burns substantially cleaner and hotter than can be achieved with the bottom lit burn barrel. (Source). The lack of oxygen below the combustion zone is impedes loss of the charcoal despite the high temperature flame immediately above it. This alows biochar to build up faster than it is consumed, at least until the pyrolysis zone reaches the bottom of the fuel column.

A handy TLUD fired Retort. The retort process works by restricting the air supply to the target feed stock for the duration of the burn. An outside heat source pyrolizes the retort contents, small openings in the retort allow wood gas to escape, but restrict the flow of oxygen in. While capable of very high yield efficiency, the open flame used to fire the retort is not as clean as can be achieved with an inverted downdraft gassifier. A common further inefficiency with smaller retorts is that much of the wood gas generated from the retort can end up not being burned. Folk Gunther's hybrid TLUD/retort demonstrates a simple configuration that neatly addresses these concerns.

2.04 What are some higher volume but less smokey approaches to making biochar for the garden?

While TLUD's can get fairly large [Link needed], a large TLUD/Retort is less practical, than a large drum retort.

A Large Drum Retort. [Expand]

The Wood Vinegar Kiln. [Expand]

2.05 How much charcoal yield can I expect?

On a dry matter weight basis, as well as an energy basis, between 20 percent, for the top lit open barrel approach, and 60 percent, for a retort under ideal conditions. 50 percent is a reasonable goal. [Sources needed]

2.06 What can I burn to make biochar?

Any reasonably dry and clean burnable feedstock will work. Woody plant material is the primary candidate. Bones are also a traditional component in Terra Preta, but one we don't know as much about. Other materials can be used conditionally.

2.07 What do I need to consider in making biochar from other than woody plant materials?

The two considerations are, what additional contaminants are being carried off as pyrolysis gas during the burn, and what contaminants are present in the ash component of the charcoal produced.

2.08 What refractory materials can I use to make a kiln? a retort?

2.09 What gases does pyrolysis produce?

2.10 How much heat does pyrolysis produce?

2.11 Is biochar worth more as a fuel than as a soil amendment?

2.12 Is biochar worth more as a fuel than its value for offsetting greenhouse gases?

2.13 What do I do if I make more biochar than I can use?

Craigslist.

3.0 How do I prepare the biochar once I've made it?

You can use it as is, especially if it is a small amount. For larger amounts, the choices are to crush, screen, add liquids, add dry materials, and to compost it.

3.01 Why would I need to prepare the biochar, as opposed to applying it as is?

There are several reasons that might apply to your situation. [Expand, obviously]

3.02 What size should the biochar be?

3.03 What are some ways to crush and screen biochar?

[For crushing, I am leaning to a mortor and pestle approach: a 5 cm dia hardwood trunk 2 m long and a 20 liter bucket with a plywood insert in the bottom.

For screening, I think a sloped screen works better than a horizontal screen for higher volumes.]

3.04 What can I do to make the biochar easier to crush?

Wetting and drying it seems to help. Crushing it with a little moisture in it helps to control dust.

3.05 Besides water, what else can I soak the biochar in?

Yes. Compost tea, MiracleGro (TM), fish emulsion, urine, ....

3.06 Can I add biochar to compost?

Yes. This will help temper the biochar. For the added benefit of odor control, consider topping off each addition to the household kitchen scrap collector with a healthy layer of biochar.

3.07 Will biochar affect the compost process?

Casual observation indicates that adding fine, untempered biochar may accelerate the composting process.

3.05 Will biochar harm the worms in my compost?

Anecdotal accounts indicate that worms tolerate up to xx% charcoal, above which reduced worm activity can occur.

3.08 Can I use biochar in my composting toilet?

Yes. Again, the added benefit of odor control is compelling.

3.09

4.0 How do I apply Biochar?

4.01 What materials combine well with biochar for application?

4.02 How is biochar generally used

4.03 What is the normal application rate for biochar?

4.04 Are there benefits to deeper placement?

4.05 Are there benefits to using biochar as a mulch?

4.06

5.0 What happens after biochar is in the soil?

5.01 Does biochar affect soil pH?

5.02 Does biochar increase soil CEC and Base Saturation?

5.03 Does biochar improve soil moisture characteristics?

5.04 Can biochar have a harmfull effect on my soil or on my garden?

5.05 Does biochar affect soil ecology?

5.06 Does biochar improve plant growth?

5.07 How much improved plant growth can I expect?

5.08 How much carbon dioxide does sequestered biochar offset?

5.09 How much nitrous oxide formation does biochar prevent?

Soil scientist Lucas Van Zweiten has observed a 5 to 10 fold reduction in nitrous oxide emmissions with some of the biochars he is working with in an agricultural setting. Generally, soil with elevated soil nitrate levels in the presence of sufficient moisture and robust soil organic matter will have higher nitrous oxide production, and thus will be more likely to benefit at the levels observed by Van Zweiten.

5.10

Earthen Terra Preta Kilns and Pollen Spectrum

I am reposting this article by David Bennet with Lehmann on Terra Preta in 2005. This reconfirms the most critical information as well as describes the original scope of the Amazonian Indian civilization itself.

Again this lays out the limiting factors and fully supports my earthen kiln conjecture.

Firstly, the maize or corn exists in an environment that mitigated against its use for purely food production. There were alternatives far better suited to the non terra preta environment, starting immediately with manioc which is a rainforest friendly plant.

Secondly, the only viable source of meat protein to these peoples at this population density was fish. Without confirmation, a pond with tilapia makes great sense. The waste from the daily meal could be readily folded into any growing seed hill. Human waste could simply have been buried in the field itself avoiding any storage. This is common practice to this day.

The making of the earthen kiln is no more difficult than uprooting the dehydrated corn stalks and properly stacking them to form an earthen walled kiln with a wall thickness of two to three root pads and an interior of tightly packed corn stalks. Obviously, any other plant material, including wood can be built into the stack as available. The earthen wall nicely restricts air flow during the burn phase and lends itself to optimization by changing the thickness. It also minimizes the amount of human effort needed which is through the roof if you are attempting to cover a pile of stubble or branches.

This gives you a kiln with vertical earthen walls and a possibly domed top that can be easily covered with earth. Again, field trials will optimize this protocol very easily. The kiln could be squared of or perhaps even circular though unlikely. The only tool to this point is a strong back or two. We have gathered several tons of corn stover over perhaps an acre of land with only a little more effort than that required to clear the field and burn the waste.

Now we must fire the kiln. The easy way is to take a clay lined old basket and fill it up with coals from a wood fire. Carry this ember charge to the center of the kiln top and tip the charge onto the exposed center and place the basket as a cap to the newly forming chimney. More clay may be necessary to widen the chimney cap. Throw more earth on top of this to prevent breakout of the fire. Keep growing earth on any breakout points that start. The chimney will serve to burn all the volatiles produced as the hot zone expands to fill the collapsing kiln until they are exhausted. Thereupon the hot zone will cool off leaving a blend of biochar, ash and earth and some root ends for the next kiln. And yes, we should have a lot of fired clay.

The biochar itself will be a range of nonvolatile combustion products that will range from even dried vegetation to activated charcoal following a nice bell curve. The material can be then gathered in baskets and redistributed into the field onto the seed hills again reducing wastage and effort.

I realized originally that the only ancient plant that could accommodate a high enough volume of terra preta production was good old maize. It just seemed an unlikely option for tropical rainforests. That is when I started looking for references to the pollen record. The article by David Bennett and Lehmann is one of those reverences that then emerged.

I would like to get a full spectrum of the pollen profile since it seems very likely that while the fence rows held the food trees, it seems more likely that they also used a variation of the three sisters using some form of convenient legume. Squashes also, of course, but not nearly as important.

The key point of all this is that a family can convert a field into terra preta in one short season, allowing them to repeat the process thereafter as necessary until the field is completely transformed to depth. Today, we can do the same thing using shovels and a garbage can lid.

Terra preta: unearthing an agricultural goldmine

Nov 14, 2005 10:36 AM, By David Bennett

Many soil scientists insist an ancient Amerindian agrarian society will soon make a huge impact on the modern world. They say once the intricacies and formulation of the society’s “terra preta” (dark earth) is unlocked, the benefits will help stop environmental degradation and bring fertility to depleted soils. Developing and developed nations will benefit.

Orellana

The story goes that in 1542, while exploring the Amazon Basin near Ecuador in search of El Dorado, Spanish conquistador Francisco de Orellana began checking the area around one of the Amazon’s largest rivers, the Rio Negro. While he never found the legendary City of Gold, upon his return to Spain, Orellana reported the jungle area held an ancient civilization — a farming people, many villages and even massive, walled cities.

Later explorers and missionaries were unable to confirm Orellana’s reports. They said the cities weren’t there and only hunter-gatherer tribes roamed the jungles. Orellana’s claims were dismissed as myth.

Scientists who later considered Orellana’s claims agreed with the negative assessments. The key problem, they said, was large societies need much food, something Amazonia’s poor soils are simply incapable of producing. And without agriculture, large groups of people are unable to escape a nomadic existence, much less build cities.

Dark earth

More recently, though, Orellana’s supposed myths have evolved into distinct possibilities. The key part of the puzzle has to do with terra preta.

It turns out that vast patches of the mysterious, richly fertile, man-made soil can be found throughout Amazonia. Through plot work, researchers claim terra preta can increase yields 350 percent over adjacent, nutrient-leached soils.

Many well-respected researchers now say terra preta, most of it still hidden under jungle canopy, could have sustained large, agronomic societies throughout Brazil and neighboring countries.

Amazing properties

The properties of terra preta are amazing. Even thousands of years after creation, the soil remains fertile without need for any added fertilizer. For those living in Amazonia, terra preta is increasingly sought out as a commodity. Truckloads of the dark earth are often carted off and sold like potting soil.

Chock-full of charcoal, the soil is often several meters deep. It holds nutrients extremely well and seems to contain a microbial mix especially suited to agriculture.

Thus far, despite great effort, scientists have been unable to duplicate production of the soil. If researchers can ever uncover the Amerindians’ terra preta cocktail recipe, it will help stop the environmentally devastating practice of slash-and-burn agriculture in the Amazon jungle. Terra preta’s benefits will also be exported across the globe.

However, even without unlocking all of the soil’s secrets, things learned in the study of it are already being brought to row-crop fields.

Among researchers studying terra preta is Johannes Lehmann, a soil fertility management expert and soil biogeochemistry professor at Cornell University. Lehmann, who recently spoke with Delta Farm Press, says things learned from terra preta will help farmers with agricultural run-off, sustained fertility and input costs. Among his comments:

On how Lehmann came to terra preta research…

“I spent three years living and working in degraded Amazonia field sites. Inevitably, if you work in the central Amazon, you come across terra preta.

“The visual impact of these soils is amazing. Usually, the soils there are yellow-whitish colored with very little humus. But the terra preta is often 1 or 2 meters deep with rich, dark color. It’s unmistakable. We know terra preta are preferentially cropped.”

On the various properties of terra preta and its modes of action…

“There are a few factors that contribute to this fertility — sustainable fertility. Remember, these are soils that were created 1,000 to 5,000 years ago and were abandoned hundreds or thousands of years ago. Yet, over all those hundreds of years, the soils retain their high fertility in an environment with high decomposition, humidity and temperatures. In this environment, according to text books, this soil shouldn’t exist.

“That alone is fascinating for us.

“Among the most important properties are high nutrient concentrations (especially for calcium and phosphorus). Most likely, this is linked to a unique utilization of agricultural and fishery waste products.

“We believe that fish residues are an important portion of the high phosphorus concentrations. Phosphorus is really the number one limiting nutrient in the central Amazon.

“Another interesting aspect of terra preta’s high fertility is the char (charcoal) content of the soil. This was deliberately put into the soil by the Indians and doesn’t only create a higher organic matter — and therefore higher fertility through better nutrient-retention capacity — but this special type of carbon is more efficient in creating these properties.

“You can have the same amount of carbon in terra preta and adjacent soils and the infertile soil won’t change. Terra preta’s abilities don’t just rely on more carbon, but the fact that its char and humus is somehow more efficient in creating beneficial properties. That’s the truly unique aspect.”

Having lived in the Amazon and studied it, how much terra preta does Lehmann believe there is?

“There are no precise numbers of how much terra preta there is (in Amazonia). No one has done any large-scale investigation of that. It’s very difficult to find out in the Amazon’s jungle environment. Suitable remote-sensing techniques haven’t yet been used.

“So (the 10 percent) estimates sometimes cited are crude extrapolations from the few areas we’re familiar with. But we know that in familiar areas there are huge patches of terra preta. These are hundreds of hectares large. When there have been maps produced of areas containing terra preta — say an area around a stream — patches are everywhere.

“It is also true that terra preta is widespread. Almost anywhere in the central Amazon, you can step out of the car and ask a local ‘Is there any terra preta around?’ and they’ll show you. It’s everywhere.”

What were the Indians growing? Tree crops? Row crops?

“There has been some pollen analysis. It suggests manioc and maize were being grown 2,000 to 3,000 years ago. In the pollen bank, these crops didn’t pop up sporadically but in large numbers.

“But all kinds of crops were grown by the Indians. Palm trees, under-story fruit trees, Brazil nut trees — all were very important.”

On the differences between slash-and-burn and slash-and-char agriculture…

“We have very good indications that the Amerindian populations couldn’t have practiced slash-and-burn and created these soils.

“It’s also highly unlikely that a population relying on stone axes would have practiced slash-and-burn anyway. The normal soils are so poor that with a single slash-and-burn event, you can only crop without fertilizer for two years at most. Then the soil has to be left fallow again.

“Primary forest trees have a diameter of 2 or 3 meters. If all you had was a stone ax in your hand, you’d find a different way to deal with agriculture than felling these huge trees every two years.

“The difference between (the two systems) is the slash-and-char wouldn’t burn in an open fire. Charcoal would be produced under partial exclusion of oxygen. We envision that happening by natives covering up piled up logs with dirt and straw. These charcoal-making systems are still being used around the world.”

How close are researchers to duplicating terra preta?

“We’re working intensively. We don’t need to take any terra preta anywhere. What we want to do is become knowledgeable about how terra preta was created and then create it elsewhere with local resources.

“Research on this is ongoing in Columbia, in Kenya. I have research colleagues in Japan and Indonesia also working on this. At the moment, there is a lot of excitement but there’s a lot of work to do.”

How terra preta could help industrialized countries…

“We envision systems based on some of the principles of terra preta. And this isn’t just for tropical agriculture. This could be very important for U.S. agriculture.

“Terra Preta could mean a reduction in environmental pollution. What works as a retaining mechanism in Amazonia could work in the United States where there are concerns of phosphates and nitrates entering groundwater and streams. We have only begun to realize the potential of how this could reduce pollution in industrialized countries.

“Luckily the principles of creating bio-char soils will be very similar no matter what area of the world you’re in. Results obtained in Brazil will be pertinent for the United States.

“In terms of widespread adoption, it’s still some way away. There are still knowledge gaps. For instance, we know there are important differences in the effects of bio-char on soil fertility depending on what material you use and what temperature and under what conditions the char is produced. That’s something we should be able to resolve within a year or two. Once that’s done, we can take the systems to Extension Services around the world and make larger scale, on-farm research plots.

“We’re already working with dozens of Kenyan farmers on this. The project only began this year. By next year, we hope to have a better idea of how this works on farms.”

Where will the bio-char come from?

“Perhaps agricultural and forestry waste products could be the answer.

“Something else that gets us very excited is a link to energy production systems (utilizing) pyrolysis...

“Really, pyrolysis is a just a complicated word for making charcoal. Prototypes of this system for commercial power plants have been developed. These create bio-oil, hydrogen and other co-products — including bio-char — from the production of charcoal.

“We want to gain a better understanding of what effects this bio-char has on soil functions. It should be quite similar to a bio-char produced in a kiln or field. Such a system will be an entry point for large-scale production and use.

“There are competing uses for the power plant byproducts. Currently, power plants either use the byproducts for their own energy needs or they sell it to be used as charcoal briquettes.

“It could become profitable as soon as some of the environmental effects — currently external — are internalized. For instance, cleaner streams, cleaner groundwater, carbon sequestration and other things.”

For more information, visit www.css.cornell.edu/faculty/lehmann/terra_preta/TerraPretahome.htm