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charcoal water holding capacity

 
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This is by no means definitive (about anything), but I found it interesting.  I had a partial bag of charcoal I made sitting outside for months.  It hasn't been inoculated, just charcoal straight from the retort.  Anyway, it's been rained on, snowed on, frozen,...you get the picture.  I needed to use some of it for my bucket toilet, but it was frozen into big, unwieldy clumps.  I brought it into the house to thaw and dry out.  The thawing worked fine.  The drying out?  Just over three weeks, it's still damp.  Considering the very, very dry, heated winter air, I found it pretty amazing that the charcoal stayed damp for this long, with no real signs of drying out any time soon.  I can imagine in soil a couple inches down, it could easily hold moisture the entire summer.
 
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I think that's a valuable observation, Trace.  I have read that and I think about it while using my biochar.  I guess old wood is the same way.  Drains in  excess water situations allowing oxygen exchange, but retains some moisture in a drought. Optimal both ways.

John S
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I had been wondering how biochar might work in an arid or desert environment. Good to know!
 
John Suavecito
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Paul Wheaton has said that he believes biochar is effective in warm areas and hugulkultur is effective in cold areas.  

I think that both can be effective in both places.

John S
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Come to think of it, I have seen this in reverse.

Years ago, we used to have parties with giant natural wood BBQs. It would take ages to burn and burn and get deep beds of coals.

One year I thought I would speed up the process by collecting wood coals to re-kindle later. Except, they were left out in a rain shower. No problem, I thought, I'll just burn a fire over top and they'll dry out. Well, I had to scramble and work for two hours to get the coal bed any where near BBQ territory. The damp char kept pulling down the temperature.

I might actually use this to advantage to control temps and reduce ash in my next char burn.
 
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I do a lot of my gardening in sub irrigated planters.
That requires a wicking soil , and thus far, I've used peat.
Peat is problematic.
Coconut coir is expensive.
Wood pellets starved my plants.
Could biochar be an economical substitute for peat in container gardening?

I have few buckets left from my last burn.
Maybe I should make up a batch of potting mix?
I generally use a dead, bagged composted manure, 50/50 by volume with a hydrated peat.
I figure my 10 gallons of char plus 10 gallons of composted manure will fill a half barrel sub irrigated planter with some left over.
Or I could use it all  for seed starting, though that is a bigger risk.
 
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William - I'm now using biochar at 25% (and sometimes even higher) in my potting mixes. It's been a game changer. I don't have to water as often, and seedlings get established more quickly. I don't have any wicking planters set up, so I can't give you any data points on that method, but I suspect that it would work.

Since I'm trying to scale up production and potentially sell the stuff, I've been testing what I make. Recently I took a sample right after crushing (damp to the point of saturation but not dripping), weighed it, then sat it on top of the wood burner for a few days and weighed it again. Before: 400g, after: 100g. So it's holding three times its weight in water. That's pretty good.

I then sent a sample from the same batch to a laboratory that does BET analysis and it came back with 300 m2 surface area per gram of material. The lab tech said that this was using nitrogen as the measurement gas and if they had done it with CO2 it would have been about double. So this is a big part of the water holding capacity...all that pore structure and internal voids.

As far as the suitability of biochar in cool climate soils is concerned, I would note that its effects on soil temperature as a function of albedo and bulk density are a pretty big deal. Even a small amount (1-5% v/v) in the surface layer darkens the topsoil a lot if it's finely ground. When Māori were first settling in NZ, they had brought crops from the tropical Pacific islands with them and needed to grow these for their energy foods. The one that they managed to cultivate successfully was the kūmara, known in the US as sweet potato, which needs a long growing season and lots of warmth. In some cooler regions, like the west coast of the South Island, charcoal from cooking fires was incorporated in the soil of kūmara beds so that they would warm up earlier in the season for planting. So this year I'm giving it a go.



 
William Bronson
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Phil, thank you for sharing your experience, its very encouraging!
I can't help thinking that a potting mix with a significant amount of char will also look very rich and fertile to any potential customer.
 
Phil Stevens
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We are visual creatures, that's for sure. And just about anyone who works the soil lusts after darkness....
 
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One thing to be wary of, if the charcoal is holding onto water so well that it doesn't dry over a fire or in central heating it also won't release the water to plants. So yes there will be more water in the soil but there will be less or the same free water actually available for use.
 
William Bronson
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Evaporation is a different process than wicking, but it's a fair point.
Still, the reported dampness indicates available moisture, which is what we want.
 
John Suavecito
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From everything I've read, tiny roots in undisturbed soil, perhaps with the help of mycorizhae, can unlock the water in something like a chunk of wood or biochar. It would be hard to imagine that they hadn't figured that out over the millions of years.
John S
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Yep, my biochar heaps are always damp, even when the surrounding soil is not. The very surface layer gets dry if in the sun, but beneath the surface is very damp.
 
Phil Stevens
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Biochar holds onto water by surface tension alone. Root hairs will encircle a piece of biochar in soil and mycorrhizae make their way into the pore structure. These two mechanisms are very effective at leveraging surface tension and mean that the water that biochar holds is readily given up to plants and microbial life that need it.

 
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Thought I would share an interesting "square foot" garden experiment I did a few years ago, in which I smashed up an amount of burnt char and put it one part of the beds and smashed up bagged charcoal in another, then turned both into the soil (which was excessively clayish to begin with). Sorta thought "meh" about my results that year... Skip forward a couple of years of no gardener effort in the form of useful composting, mulching, or other soil improvers. Then restarted gardening post-chemo and early recovery, and what came next doggone surprised me... Those two areas continue to be the best in this particular garden

That said, I may be relocating this spring, and if so I plan to do even more experiments with a combination of this trick, trenching in with some straw bales, etc. Thoughts?
 
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I've watched moss growing on my surface biochar in moist areas where the biochar acts like a wick.  In dry sun beaten gardens I've heard that this can lead to moisture loss from the soil so it's probably best to make sure it's under the surface in gardens like that.
moss-on-surface-biochar.jpg
Moss growing on garden surface biochar
Moss growing on garden surface biochar
 
Trace Oswald
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Paul Ellsworth wrote:Thought I would share an interesting "square foot" garden  experiment I did a few years ago, in which i smashed up an anount of burn char and put it one part of the beds and smashed up bagged charcoal in another, then turned both into rhe soil (which is excessively clayish to begin with. Sorta thought "meh" that year.... Skip forward a couple years of no gardenor even much useful composting or mulching/other soil improvers. Then restarted gardening post chemo and early recovery, and the what came next doggone surprised me... Those two areas continue to be rhe best in this particular garden

That said, I may be relocating this spring, and if so I plan to do even more experiments with a combination of this trick, trenching in some.straw bales, etc. Thoughts?



I would be very interested in seeing the results of your testing, however you do it.  Personally, if you have heavy clay, I would trench the straw bales in.  I had very heavy clay at my old place, and pretty heavy clay at this one.  I don't make holes in clay unless I have to.  Too often you get a swimming pool effect and things don't do well.  It would be interesting if you could broadfork some charcoal in pretty deep, along with some organic matter and see how long it would take to convert that clay soil.  I think you would still have to do a pretty substantial area to avoid making a swimming pool.  If you don't want to do a large area at a time, or prefer smaller areas to conduct different tests, I would emphasize building areas on top of the clay.  No matter what, it would be very interesting to see.
 
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Phil Stevens wrote:William - I'm now using biochar at 25% (and sometimes even higher) in my potting mixes. It's been a game changer. I don't have to water as often, and seedlings get established more quickly. I don't have any wicking planters set up, so I can't give you any data points on that method, but I suspect that it would work.



I'm having trouble finding anything near the quantity of biochar I could use. Well, to be more specific, I can't make it in my county due to local fire ordinance and I can't pay the huge transport costs for purchased char. None of the local places catering to garden inputs have it. One does have bone char but I'm avoiding that.
 
Ellendra Nauriel
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echo minarosa wrote:

I'm having trouble finding anything near the quantity of biochar I could use. Well, to be more specific, I can't make it in my county due to local fire ordinance and I can't pay the huge transport costs for purchased char. None of the local places catering to garden inputs have it. One does have bone char but I'm avoiding that.




Similar problem. I've been making it in small batches in the woodstove using tin can retorts, with crop debris as the feedstock. And on another thread there's been some brainstorming to try and come up with a more efficient design for burning straw and such into char, but I haven't tried building it yet. I'd love to be able to make a bushel or more at a time!

Enclosed burners might get you around the fire ordinance.
 
John Suavecito
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The tiny volume of biochar is why I moved from retorts to TLUD in a 55 gallon drum.  Please see other threads.   Many have other procedures for their sites.  Straw is a great amendment, but it will biodegrade quicklly into the soil.  I prefer not to till or redig the garden numerous times. That's why I dig the biochar in about 2-10 inches deep, as Greg was alluding to. Correctly made biochar should remain effective for 500 years at least. That's why it's a great way to sequester carbon in our age of Climate change.   Sounds like a great experiment, Paul, sorry to hear about the need for chemo.  I always like to hear results of experiments like this.  Wet clay is one of the best motivations to use biochar. It drains well, but retains microbes and nutrients.  We have heavy clay and lots of rain in the winter half of the year.  Many of our plants will die or fail if we don't amend the soil to prevent disease and drowning of plants and microbes.

John S
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Trace Oswald
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I think not having nearly enough biochar is a problem we can all relate to.  It takes a lot of resources and time to make large amounts.  I just make as much as I can.  If you just keep plugging away at it, the amounts add up.  

If you can't make any, I'm not sure what you do.  I guess, try other methods of soil building.  I would definitely look into making charcoal though.  It's hard to believe there is a county with a complete and total burn ban.  Maybe you can make it in the winter only?  There have to be some times you can burn.  As Ellendra said, there are ways to make charcoal pretty efficiently with little smoke, but it would be hard to make no smoke.  Maybe making it at night in a sheltered would allow it to be a little more clandestine?  
 
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How finely does everyone recommend crushing the chunks of char?  How do you find is the easiest and neatest/ cleanest way of doing this without producing a fine dust cloud of it and inhaling it?  
 
John Suavecito
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Denise, there are many other threads in this forum on those topics.
John S
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Greg Martin
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John Suavecito wrote:Denise, there are many other threads in this forum on those topics.
John S
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Here's one
Advice on Crushing Biochar
 
pollinator
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Greg Martin wrote:

John Suavecito wrote:Denise, there are many other threads in this forum on those topics.
John S
PDX OR


Here's one
Advice on Crushing Biochar



Greg, that thread you linked to was very informative.  Today is the first time I ever studied up on biochar and I am glad I did, it will definitely be added to the mix, pretty much every mix, and since I am just starting a real effort of planting and raised beds and Back To Eden areas I will be able to use biochar from the bottom up.

Fortunately I have my old, repurposed cement mixer that I will use to break down the biochar, then I will add in the water and wood chips and manure and other compost items and mix them all together and let them nourish in the compost pile for a while.

I also like the mention in the other thread about using the larger pieces in a pond filter so it can help filter the water and allow micro-organisms to grow inside the pores of the biochar to further nourish the garden.  This spring when I make my duck pond I will be sure to incorporate it into the filter system.
 
John Suavecito
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Michael,
I love the comment about reusing the cement mixer. I have seen lots of people in this forum and all over permies.com find new ways of making processes work that totally fit their situation, based on a suggestion from someone else.  I don't have a cement mixer, but I know of people who mentioned what they were doing and I either used what they did, tried it and adapted it for my use, or used the idea as an analogy for me to use something similar.  Keep it coming people!

John S
PDX OR
 
Denise Cares
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There's some very ingenious methods being used to crush biochar! Another question I have that I didn't see mentioned before is whether it's good to use softwood for making charcoal - pine and cedar?  It seems that those woods don't leave behind much solid material for crushing when burned in my woodstove.  Maybe hardwood is considered essential?
 
Greg Martin
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I love using softwood char for multiple reasons Denise.  First, I'm exploring my hypothesis that biochar formation was a result of evolution as part of the beneficial output from fire adapted conifers.  After a fire the charcoal is left as a deposit layer on the forest floor where it will eventually be covered in forest duff and will become buried in the soil.  But first it will absorb water and go through freeze thaw cycles that will cause that water to break the char into smaller and smaller pieces.  The softwood's thinner walls help this happen quickly.  Also the softwood char has a higher percentage of xylem and phloem channels leading to higher water retention than that of hardwoods.  I use a mix of softwood and hardwood for what I'm assuming will be short term and longer term breakdown into those small pieces in my soil.  Also part of what those fire adapted softwoods are doing is burning/charring out the hardwood competition so it seems like a good way to follow nature's lead, which seems like the only real path to me.

Having said all that, it's also very practical for me as line crews will leave logs on the ground when they do tree work here.  The hardwood usually gets picked up by folks for their woodstoves and so it's very easy to fill my car up with softwood logs.  I always have a pile waiting for me to find some time to do an open pit charring session.
 
Phil Stevens
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Denise, most of the biochar I make at the moment comes from pine wood and bark, mostly because I've been dismantling a slash pile on the other side of the village and burning it one batch at a time. It makes a superb end product, very low ash and easier to crush than hardwood char. I also do a fair bit of willow, as it's regarded as a pest tree along waterways here and I cut lots of limbs for stock feed when we have a drought. Willow biochar is similar to pine in its low density and easy breakdown.

Any biomass is a good feedstock. The main differences will be the ease of burning and the ratio of carbon to minerals in the finished product.
 
Michael Fundaro
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Denise Cares wrote:There's some very ingenious methods being used to crush biochar! Another question I have that I didn't see mentioned before is whether it's good to use softwood for making charcoal - pine and cedar?  It seems that those woods don't leave behind much solid material for crushing when burned in my woodstove.  Maybe hardwood is considered essential?



I only burn Pinion Pine and Juniper, mostly Juniper.  During cold spells when I keep it loaded with wood all day and it fills up with ash I find it is about 70% fine ash and the rest is a various sizes of charred wood bits.  I think the trick is to collect the bits of char before it cooks all the way down to ash.  Since I just started collecting the char a few days ago I have shoveled out the stove twice.  After letting the covered bucket cool inside the house I separate the char into the compost mixer and toss the ash to the chickens.
 
John Suavecito
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I agree Michael. When I'm making biochar in my TLUD, I douse it when the flame is just a few inches over the charcoal. That way I get great biochar, hardly any unburned wood, and very little ash.  The exact timing sequence is going to be a bit different for each system. I also think there's no problem with using conifer or whatever organic material you have, including cornstalks.
John S
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