I was reading about how people of the past made charcoal in large pits covered with soil. http://www.fao.org/docrep/x5328e/x5328e06.htm It looks basically like a large Hugleculture bed that they could light on fire but then reduce the oxygen load so it would become charcoal. From my understanding charcoal is the same thing as BioChar. So my idea I wanted to throw out is if it would be possible, and worth the effort, to build one of these types of pits but only to allow a portion of the wood to become BioChar by sealing up the pit after a certain amount of time. The result would be a mixture of wood and Bio char mixed together buried in a Hugelkultur bed all in one shot.

Adam - I saw a video a while back of an amazonian planting method that did almost exactly this. They dug a small trench where they were about to plant their crop and set a small fire in it. Once it was going they smothered it with soil and planted on top. It was supposed to "fertilize the soil" (no evidence was shown in the video, this was just a traditional approach that seemed to have been passed down in this one tribe).

Supposedly the pyrolysis gives off a bunch of complex hydrocarbons which condense in the soil and provide good fungi food, I guess the unburned wood would decay and the biochar would remain in the soil long term. THe narrator was suggesting that this MIGHT be how terra preta was formed, but no one really knows what processes were used.

At the very least this would be an interesting experiment.

Think carefully how you intend to quench in though, or you risk all your wood just burning away.

Also, the fire they showed was small (a planting hole for a single plant) and brief - probably not doing too much damage to the soil. A much larger scale fire, burning for longer, may sterilise you soil of microorganisms. At the very least you would probably need a plan for reintroducing them.

Shoot, I never even thought about what the heat would do to the life in the soil. Maybe this isn't such a good idea to do on a large scale.

What's the heat going to do? Rise. Not sterilize the soil, it's going to rise. Soil life that is 2" below the surface is going to be oblivious to the fire above. What they will notice is that suddenly the space above them has been cleared of competition and it's full of cooked food. They will be moving in while you are figuring out what your plan is to reintroduce them. Unless you are digging down to bedrock to start your hugelkultur earthpit, I'd say don't worry about it.

Last night I skimmed through "Simple Technologies for Charcoal Making" I found free on Google books. Since I only want a small percentage of the wood to turn into BioChar I think it might possibly be pretty easy to do. The difficult part it seems from the book is making sure the majority of the wood turns into high quality charcoal which is not want I want. So I am thinking a large hugelculture bed would work best. Maybe dig down a few feet and load up the wood 6 foot tall and 20 foot long. If I start a fire all along the middle then add the rest of the wood on top, let it burn just a bit then cover the bed in a foot of soil. It sounds like the heat would probably just effect the two inches of soil above the wood. That would still leave me with 10 inches not really adversely effected by the heat? I would then at some time later drench the mound in water to make sure the fire is out inside. Sounds like timing is everything. Maybe I would add some compost tea at a later date just to make sure?

My goal is to find a way to make it easier to make and use large amounts of BioChar. And what better place to use it then in a Hugleculture bed. What I have seen on Youtube making BioChar in the 55 gallon drums looks like alot of work for just a little BioChar. I just can't get over how the picutures of how the Charcoal eath pits are just big Huglecultur mounds set on fire but with some air holes. They are just too similar to not be able to combine somehow the best of both.

Here is the free Google book:
http://books.google.com/books?id=Ww-hfFDy1WYC&pg=PA31&lpg=PA31&dq=how+to+make+charcoal+in+a+earth+pit&source=bl&ots=kupp7O60Oc&sig=jbC-NqUDQui4HI3Gm8eCVva1Ow4&hl=en&sa=X&ei=FHfNUZf_D4-K9QSOnIHIDg&ved=0CG8Q6AEwDA#v=onepage&q=how%20to%20make%20charcoal%20in%20a%20earth%20pit&f=false

Adam, you're right, you don't need high quality charcoal for biochar. The 18th century way of making charcoal had a specific purpose -- make large pieces of high quality charcoal that could be used in steel making (this was before coal took over for charcoal). Quality in this application meant all the wood was completely pyrolized. This level of quality is unnecessary in agricultural biochar. If you have some that is not completely pyrolized, well maybe there is some material there that can be metabolized by fungi and it will be. So what?

One of the unanswered questions about biochar and the discovery of terra preta is "did the indigenous people know what they were doing and engineer it that way, or did they just luck into a good practice"? While there are many academics who hold forth the former, I think the latter is more plausible. Think about it, it rains in the Amazon jungle most every afternoon. If the people did a 'slash' and waited for the vegetation to dry out for a burn, they would have had to have a couple of dry days to be able to start the 'burn' part of their practice. And very likely, once they got a burn started, maybe an afternoon rain shower popped up before all the slash was consumed in the burn. Exactly the conditions that would leave you with large quantities of charcoal sitting on the ground. Now they weren't going to wait around for this charcoal to dry out so they could burn all of it, and there was too much to save for home cooking, so they just dug or plowed it under when they planted their crops.

For my own hugelkultur, I like to dig down about 8". This gives me topsoil to put to one side, and at 8" I pretty much hit the layer of clay that underlies most of the state of Georgia. I collect up scrap lumber (stuff that hasn't rotted any) and pile it up in the trench and start a fire. When the fire has burned down to the point that it looks like barbecue coals, I quench it with the hose. Can't let it burn all the way down; it's the charcoal that I want. Now I start building the hugelkultur bed, laying down rotted wood and layering it with dirt and leaves and grass clippings and spreading the biochar all through.

I think you will find that you don't have to pile up 6' of wood to start your burn. A pile 2' high is going to give you plenty of charcoal in your trench. You can then grind up the charcoal and distribute it evenly, but even that is something that earthworms and other soil critters would eventually get around to doing if you didn't. If you've got a 6' high pile and then you are going to start shoveling dirt on the fire to put it out, that sounds like a lot of furious shoveling to me. I'd rather use the hose and take my time shoveling dirt on top.

Thanks for the advise John. I am excited to try it your way with my next hugelkultur bed. Up to this point I haven't added any BioChar to my Hugle beds. This is definetly an easy way to do it and that's what I'm looking for.

I think it is also interesting about what Michael was mentioning about the small fires for single planting holes. When I get home tonight I'll search Youtube for some videos on that. Thanks for both your help.

I want top know if you tried that method out meanwhile and weather it was a success or not.
Second question is about what you burn. Can the wood be green? Can you burn small twigs with leaves on them or maybe grass clippings?
Do you actually make a fire I thought that the process pyrolysis, does that actually burn?

Angelika Maier wrote:I want top know if you tried that method out meanwhile and weather it was a success or not.
Second question is about what you burn. Can the wood be green? Can you burn small twigs with leaves on them or maybe grass clippings?
Do you actually make a fire I thought that the process pyrolysis, does that actually burn?

Hi Angelika, I haven't had a chance to try it yet. I am trying to make room for another hugle bed but no luck yet. When I try it I am going to burn wood the size of fire wood that way I can stop the combustion before it just turns to ash.

Angelika Maier wrote:I want top know if you tried that method out meanwhile and weather it was a success or not.
Second question is about what you burn. Can the wood be green? Can you burn small twigs with leaves on them or maybe grass clippings?
Do you actually make a fire I thought that the process pyrolysis, does that actually burn?

I've been doing biochar burns this week. With the cool fall weather and the falling leaves, it's a great time to get out into the garden and burn. But if you want biochar, you have to pay a little more attention to what you are doing than if you just want to get rid of excess brush and vegetation. Here are some pointers:

Rake your excess brush and trimmings up into piles small enough that you can pick them up with a leaf rake and shovel.

Let these piles sit until they have dried out enough to be good fuel.

Pick a burn spot that you are going to plant soon, like within the next few days.

Make a bonfire base with pieces of scrap lumber. Or hefty tree branches. You want your largest pieces in the bonfire base, these will end up making the biggest pieces of biochar.

Light the bonfire base on fire and as the fire dies down, bring your brush trimming piles and throw them on top. The smaller the materials that you throw on the fire -- twigs, leaves and dried grass clippings -- the more the fire is going to flare up.

After the addition of the last brush trimming pile, use a straight rake to pull the fire along the ground. As you do this, pull at the big pieces from the bonfire base and turn them over so that they can get charred on all sides.

When there is not much flame and it has died down to the point of good barbecue coals, it's time to quench the fire with the garden hose. At this point, when you rake the coals, you shouldn't see any whole pieces of wood, they should all be chunks of char.

I did a burn in my terraced garden yesterday, and today I went back and single dug the bed and planted some fava beans. I haven't tried growing these before and am looking forward to making some traditional Egyptian ful.

When you douse your fire, make sure that the wood gets as wet as possible. If the biochar can still absorb water, it will wick so much water out of the soil that all of your earthworms will look for a new home elsewhere.

Terra preta works well in humid, tropical regions, where it was developed.
Not so well elsewhere, unless you can mimic the conditions.

John Polk wrote:
Terra preta works well in humid, tropical regions, where it was developed.
Not so well elsewhere, unless you can mimic the conditions.

Georgia does a good imitation of humid, tropical regions. For about 9 months out of the year. That reminds me, I have to start thinking about putting the greenhouse back up.

Georgia does a good imitation of humid, tropical regions.

It certainly does. I remember camping out at Jeckyll Island Park while a hurricane was going up the coast.
It didn't need to rain...we were 'raining', day and night.

We built three hugelkultur beds with varying amounts of char this year. I'd love to be able to compare them scientifically but there are too many variables (sun, wind, big woodchuck den, etc) We used large half-charred logs.

They have all outperformed my expectations despite mistakes. On the tallest steepest one lost most of its soil and the logs are exposed. The soil on top is quite dry but the plants seem fine. One swiss chard seems to be growing directly out of a charred log.

I just harvested a lot of nice hay off this hugel for chicken bedding/food. Winter squash is still growing. We've had tomatoes aplenty and green beans. The very successful basil and spicy mustard greens are seeing seed,and we will save lots, enough to share.

I wish I were better at taking photos of what it really looks like here. This doesn't do it justice. The little workers on the left there are getting some leaf mould ready for the next hugelbeet

It looks like the chard likes the charred.

So you suggest simply making a usual fire and then adding the twigs. But how doe I produce charcoal this way?
I could call each and every gardener here and I get tons of twigs, which could be converted into charcoal.
Maybe I get some of these waxed boxes from the greengrocer, I use them to light our wood heater and it works great.
The thing is how not to simply burn the pile but producing charcoal. I have got enough wood ash for the garden.

Angelika,
The key to making charcoal is limiting the air getting to the embers. A simple way to do this it do to a top lit pile. Stack big wood on the bottom, make sure there is plenty of air space between the fuel to allow air. Stack smaller and smaller wood higher and higher. Light the top of the pile. Once the pile is all embers, rake it out and douse it.
Kelpie Wilson has good info about biochar. Check out her site Green Your Head.
Cheers,
Gani

I wonder what adding flour to the mix would do. I remember Paul Stamets mentioned that it is an excellent fungal food. Also I motion we call this method of Hugelkultur, Hugelchar I think it sounds nice : )

Philip Durso wrote:I wonder what adding flour to the mix would do. I remember Paul Stamets mentioned that it is an excellent fungal food.

Flour is baby food for fungi. When you make up plating media to start spores, you use about 1-2% starch (flour) and 0.5% gelatin or agar (protein) to make up your media. These very easily digestible molecules allow the spores to get a good start on life while they are hunting for a mate.

Yes, fungi do thing rather backwards from us animals. Animals are born, they grow up and sexually mature and then they mate. Fungal spores are 'born' into hyphae, they mate with the closest available partner, and then they grow.

John Polk : I was interested in your comment on October 16th, about needing to presoak you charcoal, and like an old dog with dull teeth I am worrying on it like an old bone!

The Terra preta people at Cornell seem to be telling us that the charcoal will be colonized by the fungi,and the matt of interconnecting tendrils of White Hyphae would water
the charcoal, I am wondering if the charcoal needs to be wet to keep a balance with the Soil until the Hyphae form the connections !

Scattered across the hundreds of old abandoned farms in my part of the country are big old 'Wolf' trees needing BIG notches cut out of their base to allow chainsaws with 20''
bars to cut them down, usually they are rotten in the inside, but anyway the kind of sawmill that could have been used to cut up these big old hardwoods has not been seen in
this part of the country for decades, so usually any of these trees that are cut down have their limb wood cut up for fire wood and the trunk is left to rot, and an other person
has learned not to tackle these old monsters ! these things eventually rot and then swell up to even more immense sizes being immense sponges.

I can remember going picking Crabapples after a first frost, and taking a break to set down on a sun warmed stone fence, when the young lady I was with tried to sit down on
the nearby old log and got a wet ass for her effort somehow that was my fault ! I have been prepared to believe in Hugelkultur from that day ! Big AL !

John Elliott wrote:

Philip Durso wrote:I wonder what adding flour to the mix would do. I remember Paul Stamets mentioned that it is an excellent fungal food.

Flour is baby food for fungi. When you make up plating media to start spores, you use about 1-2% starch (flour) and 0.5% gelatin or agar (protein) to make up your media. These very easily digestible molecules allow the spores to get a good start on life while they are hunting for a mate.

Yes, fungi do thing rather backwards from us animals. Animals are born, they grow up and sexually mature and then they mate. Fungal spores are 'born' into hyphae, they mate with the closest available partner, and then they grow.

Brown rice is what I have always mixed in with any of my soils. Brown rice flour along with some cornmeal is a really good feast for your fungi. Leaving it whole makes it last much longer, using a coffee grinder to powder some of the rice makes it more available. But more fungi in your soil is not always a good thing, because fungi are greedy and like a more acidic soil, just the very presence lowers your ph, to much fungi and it can cause very serious problems down the road.

Fungi despite their odd life cycle and breeding patterns are genetically more closely related to us animals than any plant on earth. Remember fungi breath oxygen and release co2 just like we do. Thats why in a biodynamic gardening setup you are leaving the layers of soil intact so that the mushrooms will thrive in 1 layer, with the ph the way they like it, and other layers will have different bacteria thriving, this has many purposes but mainly it sends lots of co2 right up through the bottoms of the plants for all the stomata to take in. Even just a few clumps of growing mycelium in a 18 gallon tote would require you to fan out the built up co2 a couple times a day or it would poison itself and never continue on to its fruiting stage.