Are Burn Barrels Really Safe for Biochar?

I think an intelligent discussion deserves to be had about the wisdom of burning in metal drums. I saw a post on the biochar facebook group about it and it started a real flame war.

If you've ever walked around old junk yards there's virtually nothing will grow in them but weed patches. This just a casual observation and could be biased of course. And there are certainly other kinds of run off and compaction to be expected in a junkyard. Completely anecdotal but certainly got me thinking.

I think the most obvious question is whether such small amounts one might think would be released through heat/oxidation and finding its way into the charcoal are worth considering in the first place. But on the other hand there's a considerable list of things that applied in small amounts are known to disrupt the mycorrhizal structure of soil. And a burn barrel is not isolated but emits smoke and how much of that smoke may contain iron and other metals.

So the amount being small isn't something that ought to be written off entirely. Many people made the point that iron and other metals are in soil naturally. But I think the difference here is it is already within the existing mycorrhizal/mineral structure in a natural form.

Is it such a stretch to think even a small film of metal particles can be detrimental to fungus and bacteria? Out of curiousity I just searched for iron + antibacterial and at least one study says this:

Do Iron Oxide Nanoparticles Have Significant Antibacterial Properties?... At present, multiple studies have been published that show the antimicrobial effect of IONPs against Gram-negative and Gram-positive bacteria and fungi.

https://pmc.ncbi.nlm.nih.gov/articles/PMC8300809/

Well, any variety of metals will interfere with life processes, that is for certain. Its why quarries become environmental dead zones when various metals enter the soil and water.

But what really got me thinking was that many people quench their biochar in a burn barrel. The rapid water/temperature plummeting could very well become a slurry of small rust and various particles from the barrel itself which has now coated your charcoal which is itself very binding to whatever is around it.

Anyway, my intent isn't to be alarmist by any means. I am also not a chemist. People have been using barrels for a while now. And maybe after a long enough time frame it becomes a moot issue. I am just saying if you are really trying to maximize the microbial/fungal life, charcoal that is potentially covered in some kind of metal particles might hinder the overall objective there.

Interesting.
I thought you would be bringing up paint, not the metal itself.
I have some retorts that are stainless steel, but most of them are regular steel.

Personal belief is the iron is a good thing and not a bad thing.  They teach in the classes that only a couple of percent of iron added to soil is bio available.  The rest mineralizes up enough that it is chemically locked up.  Bacteria and fungi tear those mineral up enough for the plants to have access to some of them.

A thin barrel from motor oil will last for years before starting to rust out. The volume of char produced in that time is massive. To my mind, the ratio of iron to char is so minuscule that you would need a forensic lab to find it. Personally, I'm not concerned -- the benefits massively outweigh any hypothetical downsides. My 2c.

Given that many, if not most, people are making biochar in metal burn barrels and are having great results from using that biochar, I rate worrying about this somewhere between very, very little to none.  That said, concerned people can easily just make their biochar in a burn pit.

If there were going to be a genuine problem I think it would have been identified by now as people worldwide are already using biochar to grow their plants and the side-by-side trials of beds treated and not treated with biochar consistently show benefits of using the char.

Regarding the specific claim of the metals themselves being a potential issue; in my location we typically have problems with lack of trace metals in our soils, and in particular iron. I've spent considerable time researching how to supplement our plants with these traces. "Free" metals in the biochar would be a win in my book.

(Our bedrock is chalk which is very alkaline and any soluble minerals wash through rapidly with rain.)

To be fair to the OP, I have no doubt a kiln made of bricks or stones/clay could produce great char. The same principles apply.

The beauty of metal barrels is that you can take them to where the wood is. The labour savings are massive.

Iron (specifically iron oxide, or rust) is a great thing to add to biochar. If you get rusty water to infuse your feedstock, then the biochar will have tiny crystals of iron oxide scattered all over its surface area and this helps with many of the attributes that we want in our soil in particular: cation exchange, adsorption, oxidation and even catalytic properties. Iron-enhanced biochar even destroys "forever" chemicals and can be reused without wearing out.

I have made about 100 burns with my system and there is no sign of wear whatsoever. As many have mentioned, there are significant increases in production in particular species, including many mushrooms, after biocharring.  I think it is a good concept to bring up , but at the current time, it doesn't seem to bear out as a serious problem.

John S
PDX OR

John Suavecito wrote:I have made about 100 burns with my system and there is no sign of wear whatsoever.

Good point. My barrels stay out in all weathers, sometimes full of wet char, and yet they last for years.

If the char inside is a little ashy and sketchy, I spread it on a grassed hillside that was a garden long before I moved here (I found plant tags when I dug in) and perhaps will be again long after I move out. The grass doesn't care (it's mostly brome, deliberately planted as cover by former owners). It will just add to the "top mulch" needed to build soil on a sand hill. Somebody down the road will make use of it, and if they find lots of char they may realize somebody was building soil a long while ago. Personally I think that's a pretty cool handoff amongst knowing people.