Topic: Can compost create charcoal? (see Terra Preta)

[Vinlander]

When I dig woodchip out of the communal bin I occasionally see stuff that looks charred. It can even look like ash. I'm pretty sure there's no way it can get in there from fires - the burning is too incomplete anyway...

I'm very interested in this because the Amazonian cultures produced incredibly fertile black earth (Terra Preta) by partial burning of what we would compost.

Hence the people desperately eager to take your money for "extra pure" charcoal to use as a soil conditioner - they are even happier to charge you many times more than (already incredibly profitable) ordinary  barbecue charcoal, despite the fact that the Amazon method would have produced hundreds of times more tars etc. than normal charcoal (the Amazon peoples probably just composted the fresh stuff to 'clean' it - the whole point about char is that it doesn't decay into CO₂- ask any archaeologist).

Anyway to get back to the point - a composting method that produced even partial charring without fire and smoke would be enormously better for the environment.

Has anyone tested the charcoal content of that ashy woodchip?

Does anyone know the conditions that produced it?

Cheers.

[ancellsfarmer]

Consider these possibilities. Woodchip is mainly the byproduct of tree surgeons clearing of brash.They tend to use chippers that have a capacity of around 70mm diameter, such as Timberwolf. Larger timber is either logged and transported to market, using the same truck?; or burnt on-site to comply with environment rules. This would result in some charred remnants, probably cleared from site, with ash, with the next load of chippings.
Composting occurs, ideally at between 45-60 deg C. Wood ignites from approx 180 deg C.
There is the theoretical possibility of woodchip heating to high temperatures in large heaps, so the industry stores in heaps of up to 3metres.
Consequently your material may be derived from an overbig storage heap, although self igniting heaps are rare and the probability, low.
Charcoal needs inoculating to be useful within the soil environment, the addition of crushed charcoal to your compost heap enables this and is to be recommended. However charcoal is relatively expensive , bio char even more expensive and the beneficial effects difficult to evaluate, certainly on cost effectiveness grounds.
I recommend the attached video clip which prompts further thought as to something we may consider for ourselves. I further recommend all the others in this series, for they are a thought provoking stimulus to any permaculture interest
https://www.youtube.com/watch?v=Yy9k0_sX1xU

[Vinlander]

It's very possible that it was charred by being at the centre of a huge heap that didn't quite self-ignite.

That would raise the possibility of getting the same effect from a more manageable sized heap inside a well-lagged steel container... A layer of granular charcoal would probably be an ideal heatproof lagging material - though you might want to give it a CO₂ atmosphere (not rocket science - hopefully).

I didn't consider the possibility of the pile being contaminated with ashes from a previous fire - but that's mainly because the structure of the original plant material was clearly still there - it was mainly quite thin twiggy stuff with some leaves still on (but grey).

It didn't look anything like the leftovers from a fire - and normally twiggy stuff is the first to burn to nothing at all.

However it is possible that it was twiggy stuff that was out of reach of the flames but was charred by radiation - it's entirely possible but pushes the probability much, much lower than 99% of what you normally get from a dead fire ie. partially and fully charred wood left over from big pieces that resisted the fire until it was put out.

The next time I find some I will try and separate it out for closer investigation.

Incidentally, the "cheap" biochar advertised at the bottom of the page works out at £1 per LITRE but only gets that price if you buy 900+ litres. That's about £4.50 per kg - 3.5 to four times the retail supermarket price of barbecue charcoal.

The video was interesting, but if it came to managing an actual burn I'd personally favour the oil drum method, and the giant steel tanks used by woodsmen will be even more efficient - it's just a pity that nobody has tried to collect the tar vapours as an alternative to crude oil.

Yes, barbecue charcoal is mildly hydrophobic - but that disappears if you soak it (to keep the dust down - yes urine is probably ideal) and crush it before soaking again.

Cheers.

[ancellsfarmer]

"(not rocket science - hopefully)."
Charcoal, nitrate of potash, S. what could go wrong!!
Remember the ancient Chinese were only trying to compost, or that was their excuse.......

[Digeroo]

Woodchip  which has gone mouldy might look a bit like burned stuff.  The fungus strands can look ashy.