A Little BioChar Experimentation

[Red-Stars-in-RI]

I had what appears to be an increasingly rare thing these days - a weekend with no plans and decent weather to work around the property. I decided to do a little biochar experiment with a few different inputs while cleaning up some scrap wood. I occasionally make biochar for use in my coops (to cut down on odors) and then go into the chicken run compost system. I've usually made biochar with little bits of scrap wood, but wanted to branch out into materials. I was especially interested in using an invasive species and see how that worked with biochar.

In this case, I picked Japanese Knotweed, which I thankfully don't have on my property but see stands of it all around town. On the way home from the transfer station today I stopped and harvested a little bit on the edge of the road. Since knotweed will spread from a small fragment, I was very careful not to drop even a leaf.

I chopped up some knotweed and put in into one of my biochar kilns (ok, it's a small hotel pan).

Next up, something I have a lot of around my chicken run compost system...avocado pits. These things take forever to rot, so they surface up in the chicken run compost all the time. I started grabbing them and putting them in a paint bucket to see how they'd char. BTW, people say "avocados are poisonous to chickens", but the parts that are toxic are the skin and the pits....which chickens aren't going to eat anyway.

I used some scrap wood for a "control". BTW, those are metal paint cans I use to char in. Very small quantities, but I'm hoping to build a larger setup at some point soon.

 

[Red-Stars-in-RI]

Next up was putting the hotel pan and two metal paint can with our three materials into the fire ring, and starting the fire.

Once it got going, I threw a little extra Japanese Knotweed in, just to dispose of it.

In between adding more wood to the fire, I took the opportunity to sift a little chicken run compost...planted a small patch of grass seed, and now it has a nice compost base to help it grow.

 

[Red-Stars-in-RI]

The Results

After the fire cooled off, I opened the three containers to see what I could learn. The wood, as expected, turned to char pretty well, in line with prior burns I've done. Its nice char but the density of it makes it a little tough to crush. The can wasn't full, so the amount of char produced is pretty small compared to a well-packed can.

The avocado pits mostly charred, although a few didn't. They are very dense, so they won't crush well, but there was solid yield. Not bad for a waste material that won't compost well.

Finally, the Japanese Knotweed. The yield was very small, which is not shocking since the weed was harvested green/wet and it's obviously a much less dense input than wood or avocado pits. But the char was complete, and the little bit of char that was produced crushed to a fine power with no effort.

I'd had a hypothesis that this would be the case, and it was nice to validate that.

I'll continue to make small batches of biochar in the fire pit as time permits, using all three of these inputs....but as I explore ways to make biochar in slightly larger batches (think 55 gallon drum instead of paint cans), the idea of using an invasive like Japanese Knotweed is really appealing.

Not only does it make a really easy to crush char, but one of the few chemical-free ways of killing knotweed involves cutting it back repeatedly in hopes of weakening the roots.

If I can make char while wiping out a few of these nasty plants, that's a win-win situation.

 

[Hummingbird Meadows WA]

How long do you leave your "biochar kilns" in the fire? Also, do you think blackberry "bushes" who make good char? This is a really great idea and I would love to try it!

 

[Red-Stars-in-RI]

How long do you leave your "biochar kilns" in the fire? Also, do you think blackberry "bushes" who make good char? This is a really great idea and I would love to try it!

With the paint cans/hotel pan, I just leave the "kilns" in the fire until it burns out. My guess is that it'd take a couple hours to char, maybe less...depending on the dryness/size of the materials and the heat of the fire.

Once things get hot, you'll see steam blowing out the holes in the paint cans, then shortly after that the gasses come out and catch fire (which looks pretty cool). My understanding is that once this stops, you likely could pull the cans out and the char would be "done".

I hope to make a "batch" system this summer. If it works out, I'll have a better idea of how long different things take to char.

I would guess the blackberry bushes would be decent for char. You'd probably get a yield somewhere between what you'd get with wood and what I got with the knotweed, since the blackberry is likely in between those two in terms of moisture content and thickness.

If you give it a try, let us know how it works out!

 

[Red-Stars-in-RI]

It's been a while since I posted about biochar. I've done an experiment with a 55 gallon drum, but found that my fire ring wasn't big enough to to get it hot enough. While I shop for a larger fire ring, I realized I had a 20 gallon trash can that would fit well. I drilled a few holes in the side and figured we'd give it a go.

My son and I stopped at a roadside patch of Japanese Knotweed, and carefully cut and stuffed as much as we could into the trashcan. Again, knotweed can root from a very small fragment, so being super careful was key. Once the knotweed was in the can, I kept the cover on tight except to take a quick photo.

That's the can of knotweed, with the fire ring and the metal paint cans I use for smaller batches of biochar in the background.

Close-up of of the knotweed...we used the entire plant, from woody stems to smaller tops and leaves.

The difference from the springtime experiment is that this knotweed was dormant, and likely had a lower moisture content than the "green".

I got a fire going. One of the reasons I'm interested in using invasive species for biochar is that good hardwood is going to create the most weight/volume of biochar, using good wood for biochar production feels not quite right. So, other than a few spruce logs from the bottom of my fire pit wood stash, all the wood we're burning are branches that fell in the yard and would need to be picked up anyway.

I built the fire up quite a bit bigger than that to make sure I had enough heat. My son loves a good campfire, so he was happy to hang in the backyard feeding the fire and grinding some of the biochar we made yesterday.

The holes in the trash can were in the side, facing the heart of the fire. That way, any gases produced in the char process would burn off. In this way, the biochar process actually helps itself along by literally "adding fuel to the fire".

After a few hours of feeding the fire while mowing up lots and lots of leaves for the chicken run, I pulled the can out and opened it up.

The charring process was complete, which was nice to see. The volume had been greatly reduced, as expected.

30 seconds of crushing with the fire poker stick reduced the particle size and volume significantly.

Is it worth all this work to get maybe a gallon of biochar? Probably not. It is nice in the coop to help fight odors, and in the compost to absorb nutrients, improve water retention qualities, and generally make plants healthier. It also sequesters carbon in the soil, which is good for both the earth and "The Earth".

Adding in that the input was a nasty invasive species, that feels like that adds another layer here. We didn't make anything close to a dent into the one small patch of knotweed, but if we did this regularly, would it help keep the knotweed in check? It couldn't hurt.

One family making small batches of biochar in this manner on the occasional weekend won't change the world, but it might improve our little corner of the world and enrich our soil a bit. If a lot more folks did the same, though, it'd be really interesting to see what kind of impact we could have.