Recreating Terra Preta

For a long time I have been fascinated with terra preta - the endlessly fertile anthropogenic soil of the Amazon. I have been collecting data on it for a long time and am now attempting to recreate it in my own garden.

If this kind of land-hacking appeals to you, you will love my new video showing the creation of a terra preta bed:



Will it work? The centuries will tell!

I added everything I knew about that was in the original terra preta, including yellow clay, food scraps, bones, seaweed, biochar and even pottery shards... what a lot of work! But I'll bet it's worth it.

What do you guys think?

I have also done reading about Terra Preta, and often found comments that implied that since we don't know how they did it, or over how long a period it developed, or even why they did it (did it start as just a way to get rid of garbage and then they discovered how great it is?) how/why should we be so bold as to try to "reproduce" it. I think, David, you've clearly identified why.

We know that Terra Preta has made what's generally low-sustainable soil into long term productive soil. You've identified that you've lived in areas where the soil is poor at holding nutrients. So I think it's awesome that you've made an effort to combine the things that Terra Preta seems to have with what your current soil is missing. I did not notice a single thing in your description that I would think would cause harm, based on your description of your soil.

I personally think from my reading that it's important to build the "Terra Preta Clone" in the environment it will be supporting. There is no reason to believe that micro-organisms are the same over the world, so I think that encouraging and supporting the locals is important.

In my climate, I deal with lots of winter rain when not much is growing, but unlike you, I've got a lot of clay mineral soil just millimeters below the surface in many areas. Our "back field" is much more fertile due to years of pastured poultry and worms, but even there, I can feel my feet slip against wet clay when heavy rain has raised the water table. Thus, if I were to make a "Terra Preta" experiment, I'd be looking for a source of sand! As I'm getting older, my soil building experiments lately have combined some of the same things you've identified, but instead of digging down (trust me - I'm just not up to 5 hours of pick-ax work to get 30 to 60 cm down! Sorry - that's 1-2 feet in American.) I've been making raised beds, about 75 cm (30 inches) tall, but essentially doing what you are doing - layering biochar, dead chickens, woody debris, finished compost, dirt, leaves etc. Having watched this video, I'm wondering if I shouldn't up the amount of biochar, but at the moment I can only make it in small quantities.

I really hope you observe your experiment well and remember to report back. Many areas on this planet are loosing soil fertility and the soil itself, so building soil is something we could all be trying to do for the future.

I had a similar thought, but I was thinking of mixing compost (biochar is always included in my compost), sand, azomite/sea-90 in a cement mixer and broad forking the mix in.  I have pretty heavy clay already.  I haven't gone to the the trouble of tracking down broken pottery yet, but I thought that if I did, the cement mixer would smooth the broken edges down.  I'm not sure how helpful pottery would be here since I don't really need the water wicking capability here.  I may try this with one bed this year just for kicks.

Trace Oswald wrote:I have pretty heavy clay already.  I haven't gone to the the trouble of tracking down broken pottery yet, but I thought that if I did, the cement mixer would smooth the broken edges down.  I'm not sure how helpful pottery would be here since I don't really need the water wicking capability here.  I may try this with one bed this year just for kicks.

All pottery is not created equally either - so I would want to at least try to research the characteristics of the pottery the locals were using in the original Terra Preta.

I hope that adding biochar should help my heavy clay be lighter and less water-logged, but I don't have enough to really test that theory.

I like the SEA-90 idea, too. And yes - not all pottery is created equal. I have had a hard time finding data on traditional methods. A local pottery studio is saving me shards now, though, and it's bisque-fired unglazed stuff. Hoping it's close.

"I personally think from my reading that it's important to build the "Terra Preta Clone" in the environment it will be supporting. There is no reason to believe that micro-organisms are the same over the world, so I think that encouraging and supporting the locals is important."

Yes. I added rotten wood from the forest for that reason. No telling what the differences are, but I want to encourage the fungi from my area to move in.

Regarding the pottery shards, on a volume basis they will provide a VERY high CEC.  One option may be to use calcined clay products that are sold a lot for sports fields.  Having said that, based on what I read about the shards in the terra preta soil that would seem like maybe a poor mimic.  What I've read is that the terra preta shards have plant material in them and are low fired.  For me this indicates that the charcoal was being produced for cooking earth oven style and that the food was likely wrapped in leaves and this leaf wrapped package was encased in clay to spread the heat and make cooking more uniform.  The plant matter in the clay would then be something fibrous, like grass, in order to reinforce the clay and keep it from cracking during the firing.  You'd then bury this packet of food in the charcoal you made in your pit and bury the whole thing with the soil you dug out and let it slow cook.  When done you break open the clay, which is now low fired and has small channels from the plant fibers (how cool for soil application), and produces the "pottery chards".  Any wastes from these meals, like the chards, bones, etc all get thrown back into the pit with the biochar and this becomes a planting space.  Quite possible there were some other steps after that, like using that pit as an outhouse space since the biochar would absorb the smells and nutrients from that very effectively.  They would just keep making new pits for each meal big meal and the soil would
become amazing.  That is my take from making biochar and ruminating on this for the past 15 years.

Trace Oswald wrote:I'm not sure how helpful pottery would be here since I don't really need the water wicking capability here.  I may try this with one bed this year just for kicks.

Trace, the pottery chards and the biochar will both help make your soil drain amazingly well due to their granular texture, like coarse sand, but unlike sand they'll also hold onto water and nutrients....thus amazing soil components.

Jay Angler wrote:

I hope that adding biochar should help my heavy clay be lighter and less water-logged, but I don't have enough to really test that theory.

Jay, this has absolutely been the case on my land.  Wood chips and charcoal/biochar made a huge difference for me.  I'm starting a few new areas this year and I'll be using the same, just toying with the idea of broad forking those materials I mentioned in deep, rather than laying them on the surface to get established, and then going back to my "traditional" way of just piling things on the surface.

Greg Martin wrote:

Trace Oswald wrote:I'm not sure how helpful pottery would be here since I don't really need the water wicking capability here.  I may try this with one bed this year just for kicks.

Trace, the pottery chards and the biochar will both help make your soil drain amazingly well due to their granular texture, like coarse sand, but unlike sand they'll also hold onto water and nutrients....thus amazing soil components.

Any thoughts on how large the pottery pieces were in terra preta?  

Shards are typically small. Large pieces would have to be sheltered over long periods to survive. Small shards are more likely to be moved by mechanical disruption than to be broken by them.

I don't know if adding fired clay to clay-heavy soil will do much. It might be a question of the clay already serving the purpose filled by the shards.

But if I were working in an area deficient in clay, or in qualities that clay provides, and I wanted an available pottery shard substitute, I would experiment with hydroton, or whatever else expanded clay beads for horticulture and hydroponics are called. Mechanical action in soil amended with whole hydroton beads would break some of said beads, creating edges akin to what might have been seen in the original instances of terra preta creation.

In clay-heavy soils, I wonder if it would be a good idea to think about an in-soil pit burn, wherein you excavate into the clay, perhaps even shape airflow channels to better control and stifle oxygen supply, and maybe even a clay soil cap for the pit fire. Such low-fire conditions might be exactly what was experienced if raw clay had been used to wrap food packages that were then cooked in a coal bed or oven. It is probable that something analogous to pottery shards could be cooked out of the native clay in the ground.

Sounds intriguing, anyways. I would love to hear how this develops. Good luck, and keep us posted.

-CK

Trace Oswald wrote:
Any thoughts on how large the pottery pieces were in terra preta?  

I agree with Chris that I would expect a lot of small pieces, though the online pictures usually look like this one:

But my assumption is they pick out the big ones for these pictures....little shards aren't as exciting to take pictures of I'm guessing. :)

I am using a lot of the same ideas as you all are. I also became inspired by reading about Terra Preta.  I am digging the biochar down to the depth of the shovel blade.  I have read about this being recommended in a few different sources. I place it around the drip line of the tree or bush where I'm installing it. That's where the roots are most actively growing.  I have installed some cracked pieces of pottery and rotten wood as well. We have clay that drains poorly. I've improved it over the years with wood chips but the biochar not only helps drainage, as has been mentioned, but helps the soil retain the minerals during our winters of steady drizzle.  I have published here in this forum how much increase in productivity it has made the last two years and I will continue.   Some key factors of the need for biochar seem to be rain, needing drainage, and soil that can't hold onto nutrients. We have maybe 3 out of three and it has really helped a lot here.

John S
PDX OR

Thank you for the video, and I saw later video, that shows how well tomatoes and other plants grow there. I am wondering, if this would work in sandy soil with high ph as biochar is alkaline. I wonder if soil organisms would neutralize it or not?

In sandy soil that drains too fast, people have been less motivated to crush their biochar into tiny, sand-like pieces. The larger chunks manage to hold onto moisture deep in the soil if you dig it in, or eventually if you mulch on top of it. I imagine that organic material mulches would be a key strategy in sandy, fast-draining soil anyway.  The fertility aspect sometimes takes longer to help, because it is not so quickly developed within the chunks if they are larger.  Inoculation is still advised though, by most experts I've seen.  In that situation, adding sponge like pockets of moisture is seen as more crucial than immediate fertility help.

John S
PDX OR

Hey guys. So nice to find this topic. I have been researching Terra Preta de Índio for a while now and I have visited some sites where it exists and the idea is fascinating. I am Brazilian and met natives from the Amazon, my family has a long time relation with the cause. I liked the video very much, I have been struggling with an idea on how to even start the process, and this video gave a direction to follow.
A few things I would like to add to the discussion:
Terra Preta wasn't something they built as a product for a special purpose. It was part of their lifestyle, of their way of surviving and thriving in that harsh environment. Natives tend to think of themselves as just another player in the forest game, not the main ones, having to develop a way of being that allows them to have what they need and ensure that their kids also thrive, but not by acting over nature but according to it. They don't accumulate, everything has a purpose. They find a place to make their homes, they clear the jungle, build houses with that material, and there is fire going on all the time, for cooking, smoking stuff, rituals, the cassava flour making process, and every utensil is made for a reason, they don't keep a shelf full of different bowls and stuff. they make what they use and that is that. If something has finished it's purpose it is discarded. But they do it in a way that cycles it back. They stay in a place for maybe 2 to 4 years, take everything down and move to another location. They keep doing that in the same area but never stay in a place for too long nor make it too big and crowded. War was something sacred and holy to them and almost all of them were cannibals, eating their enemies and deceased in a ritual. Nowadays things are different but this puts a light in the thinking process.
They would use an area, grow crops, hunt, make war, breed and after a while they move, and while taking it all down they break the pottery and spread it around, burn the houses and fences down, leave the bones and scraps there, mulch it and let nature do its thing. When they come back, after a while, the soil is richer and they repeat it. This went on for thousands of years.
So first, the best we can do is a poor imitation, but we can use the principle: look around and figure how can you use what you have and cycle it back? Burning? Burying? What is missing? How can I use what I have to fix that? What can I do different so it will be easier to cycle back and make the soil better?
These are just provocations, to enrich the discussion.
I would bet on mixing everything in layers, lots of biochar, bones, clay, broken pottery, inoculate with IMO, rotate crops and leave the soil to rest from time to time, letting the native spontaneous plants grow, then take it all down, more layering, grow and rotate crops and so on. Biochar I guess is a must, also bones and scraps. The rest is going to depend on your local reality. But I think there is no sense in bringing in stuff from far away, has to be done with stuff you have available around.
I hope to see updates of this. Gonna try it myself too

Thanks Luis,
That's a very helpful perspective.  We can't recreate exactly how biochar fit into their lives, but we can try to learn from what they did.
JohN S
PDX OR

How did it last throughout the season? Did you dig any of it up to see what it looked like at the end of the season?

As a potter...I've been making " paper clay", which is a slurry of soaked paper ( toilet paper) added to clay slip, then dried out to be workable. This is not unlike the example of clay coated fibrous leaves encasing food to be baked in woodfire. The cellulose fibers make miniature channels after the clay is low fired & can even be used to make water filtering vessels.
So, maybe like biochar, it is a place where mycorrhizal fungi can establish a home?

Chris, that sounds like a great soil additive, much like the pottery chards that are found in terra preta.  It could be a great water and cation sponge that improves drainage, so wonderful.  If it wasn't fully burned out it may even have some of the biochar chemistry benefits from the residual charred cellulose.  

One thing that I’ve noticed is that the native clay here (found in patches) is very brittle, and when I make seed balls, it always improves their plasticity to add milkweed seed fluff. I’ve also heard of asbestos being used to the same effect, but have no desire to repeat the experiment. Perhaps this would work too? I’m not sure.

In the process of making a small terrace, I added layers of charcoal, flour/forest soil mix (to get the microbes going) and green matter. For better or worse, the green matter rooted and sprouted (comfrey had immature seeds!) and now there is the most healthy and colossal comfrey patch I’ve ever seen. They’ve also overshadowed the baptisia. Time to dig up and replant!