Lazy Biochar : just water your burnpile?

Hiya
Simple but straitforward :

Start a fire from any scrap wood and branches that won't fit the woodchipper
When the fire collapse into amber, water it.
You end with a pile of charcoal.

The idea here is not to be efficient in term of charcoal produced; but the work involved is minimal and the pile can be huge (much bigger than any metal drum... )

My question: any big drawback with this method, that would make the biochar not suitable for gardening, for any reason i'm missing??

(yes, some pieces of wood won't be totally transformed intocharcoal... then i guess it's just like having abit of woodchips in the mix... )

Thanks =)

I do that sometimes with big brush piles. It works in a crude way, but it's hard to have any sort of quality control. A lot of char is lost to ash because there's too much oxygen available, and there's a lot of half burned stuff and "tar char" as well.

The goal is to cook it down to carbon, with all the volatiles and tars cooked away, but without allowing it to burn to ash. That means controlling oxygen.

It's much better burning into a trench or pit because you have some control over the oxygen. You can keep packing it to keep air out as it finishes cooking, or even shovel hot coals into a barrel to finish before quenching.

Partially burned pieces are torrefied wood, which will not easily degrade like wood chips. It's best to separate and reburn that stuff.

If you do the above ground method, running it through a coarse screen will pull out a lot of the unburned stuff, and running through a very fine screen will get rid of some of the ash. Then you can test the remainder by rubbing it in your hands -- if it washes off with only water, no soap needed, you have decent char.

I like to use burn pile biochar in my garden, but when my neighbors make it (as encouraged by yours truly) it seems to have a higher ash content than mine. As Douglas mentions, char is lost to ash, which happens as the wind gets into the pile. Burn pile biochar can have an elevated ash content, especially if made on a windy day.

Ash brings causticity. Causticity is good for some things, so much so you may want to dry quench (soil, metal lid over a pit fire) the pile and use the biochar quickly (within 2 weeks) as the causticity (good for making biochar soap I would think, sweetening soil pH) is gradually degraded by a natural weathering process (as oxides convert to carbonates).

If causticity is not your friend in terms of soil use, no problem, you can rinse the ash off before you use it. A water quench does some of that. You can leave high ash biochar exposed to the weather, and forget about it for a year.

You can compost unweathered elevated ash biochar; the alkalinity supports biochar's characteristic ability to accelerate food waste compost and speeds up any aerobic compost process prone to go anaerobic (pew). Again, a little bit of ash is not necessarily a bad thing.

I am sure there is an upper limit of ash content for feed palatability, but burn pile biochar's highest and best use might be as a feed amendment for chickens, pigs, and cows. If you have any of these critters, I wouldn't be surprised to see them get onto your biochar pile while it is still steaming from the water quench, pecking and nosing through it, looking for some sweet biochar to eat. Pigs, chickens, and cows that have access to charcoal in their diet are generally healthier and gain weight faster.

Thanks a lot, that's already quite essential and helpful information
I'm not really worry about ash... soils are really acid here and all the ash from the fire place goes for to the garden. The tar wood might be more of an issue ? But does it do anything negative ? (let's say, compare to... a small rock in your garden bed... )

One reason i'm asking all of this, is because here in portugal, all the locals do big burn pile in the spring an fall, just for the sake of getting rid of the biomass they produce (they don't care about mulching, they use synthetic nutes'). I understand they try to reduce the fuel in case of wild fire.

But if we could teach them to just turn off the fire with water, that's not much of an extra effort, and they might ( the probably is thin) see the point !
That would be already that much carbon that doesn't end in the atmosphere...

Antonin chaozone wrote:The [torrefied] wood might ... do anything negative ?

Not that I am aware of.

Antonin chaozone wrote: reduce the fuel in case of wild fire. But if we could teach them...

Are you aware of the upside-down camp-fire build (many examples on youtube)? They are nearly smokeless, thus the attraction for campers.

Most burn piles are bottom-lit smoke bombs. But all that smoke is flammable and a missed opportunity. Permaculture design opportunity. Design your fire to employ the flame not just as a fuel reduction tool, but also as an afterburner to consume the smoke. If air quality is a concern in the area, folks who want to be good neighbors are the best candidates to approach. They have the incentive to raise their pyromantic skill level to have nearly smokeless fires.

Bonus: Because the BTU's of what would be smoke turns to heat, the top-lit pile is going to heat-distill the wood gas from the char more efficiently and quicker, so, bonus, the potential char yield is much higher than for a bottom lit pile.

Top-lit piles takes a little more effort to construct and manage, but the extra effort is worth it.
https://biochar-us.org/sites/default/files/learning/files/Smoke-Into-Biochar-flyerfinal.pdf

You don't have to water quench to get the charcoal, although that is ideal; you can rake the embers out to the fringes, away from the most heat.
You can quench with dirt like when closing an ember-bed cooking pit.

After the potential biochar yield, the other collateral benefit of a top-lit pile is that, with the heat center further up in the pile, not as much of the underlying soil gets sterilized. You can see the difference in plant and fungi recovery for many years afterward. If the woodlands are being used for grazing and foraging for mushrooms, better productivity help might motivate adoption.

It may take 3-generations for upside-down burn pile fires to supplant bottom-lit smoke bomb piles for fuel reduction, but the practice is so superior, the potential for adoption is high. Just have to find the creative community needed to start it off.

Antonin chaozone wrote:I'm not really worry about ash... soils are really acid here and all the ash from the fire place goes for to the garden. The tar wood might be more of an issue ? But does it do anything negative ? (let's say, compare to... a small rock in your garden bed... )

Personally, after burning I rake the pile thoroughly and pull out all the unburned material I can. If it slips through the teeth of the rake, I don't worry about it too much. If it's really low quality char, it will go into the orchard (after some inoculation) rather than on the garden. Natural fires generate a mix of good char, tar char, torrefied wood, and ash -- and natural soil processes eventually deal with them.

Remember that a large reduction in quantity of biochar is no small thing.  It's expensive but also highly valuable.  If you're in a dry area, you probably have alkaline soil, so you want to be careful about adding too much ash.  The main goal with biochar is housing for microbes.  If you have less biochar, you will have fewer of the crucial interactions that create soil health, less drainage, and less moisture in the soil during the hot season.  If made well, it's nearly permanent, but most people will not create as much biochar as can help them while they own the property, so a large quantity of biochar is a good thing.

John S
PDX OR

Given the OP's situation -- acidic soil and large volumes of agricultural slash being burned for disposal -- I think he is on the right track.

The challenge is to increase the char volume and quality in a way that can be widely adopted in his area.

Yep, that's exactly what I was saying.