Does crushing biochar produce a meaningful change in the overall surface area of its structure?

Dan Fish wrote:Greg! I hope you circle back around and see this.

I am on a biochar kick currently and I just saw this post. Can you provide more info to expound on what you posted here? I have had the idea of exactly what you are saying, but always at least roughly crush my char, both to make spreading it easier and because it seems popular opinion says it increases surface area.

Thanks!

Honestly I have often wondered about the idea of creating more surface are by crushing.

I mean, *technically,* there should be a marginal increase in surface area each time a piece breaks apart simply through the same mechanism that breaking a pencil increases its surface area. But that isn't the type of surface area increase we should really be looking at or concerned about with biochar.

I personally suspect that the biggest benefit of crushing is that it is easier to spread over a larger area and then to mix more thoroughly into the soil - both directly by us as well as by worms and other various animals and mechanical processes, etc over time.

I'm not entirely sure what the benefits of keeping it in chunks are or would be aside from not having to breathe as much of the dust, generally being easier to work with , fewer (unnecessary?) steps in the process... potentially easier to see where you have already made your amendments, I suppose...

John Warren wrote:
I'm not entirely sure what the benefits of keeping it in chunks are or would be aside from not having to breathe as much of the dust, generally being easier to work with , fewer (unnecessary?) steps in the process... potentially easier to see where you have already made your amendments, I suppose...

In the context of the chicken coop, the "less dust" one is huge. In addition to air quality concerns (already not great in many chicken coops) there's the whole "black dust makes black footprints on eggs" thing.

Crushing is not about releasing nutrients from the biochar. It's not a fertilizer.  If you've got chickens, great. They may do all of the crushing you need.  I don't and can't have chickens, so people like us need to find other ways to crush the biochar.  Most biochar is from wood. The chunks I see coming out of the oven are 3" by say 5".  That's way bigger than helpful.  Much smaller chunks are going to distribute the nutrients more efficiently.

It's about improving access to the "microbe hotels" and improving the texture of the soil.  Biochar infused soils retain much more moisture and nutrients than sand and allow much more airflow and water to flow than clay.  As the texture improves for greater airflow and moisture and nutrient flow, mycelium is able to travel much better through the soil.  Mycelium and plant roots are constantly expanding, dying back, and adjusting through the growing season, and even in the dormant season to a lesser extent.   They and other microbes are the jazz musicians of the soil. The tree, bush or plant is the song.  They listen to the weather and conditions and make their music.  The microbes in a quality soil are resilient and they can adapt to the conditions that are at hand.  Lots of nutrients? Great, we'll grow a lot.  Really cold temps? Let's cut back and wait it out.  Getting hot and thirsty? Let's use our soil food web to find moisture, maybe inside that large chunk of biochar that nice gardener left here.   Lacking phosphorus or other nutrients? Let's talk with our "team", and find out where some is nearby.  Maybe near that native lupine flower.  Need nitrogen? There are some alders, beans, and some autumn olive shrubs nearby.  As Elaine Ingham says, nutrients in the soil aren't optimally placed there in fast-dissolving synthetic ways.  They are unlocked by the biology in the soil.  Crushing the biochar improves the ability of the biology in the soil to unlock the nutrients and get them where they need to be.

Crushing it makes it so the soil can adapt much better to getting what the ecosystem needs to the place where it needs it.

John S
PDX OR

John Suavecito wrote:Crushing is not about releasing nutrients from the biochar. It's not a fertilizer.  If you've got chickens, great. They may do all of the crushing you need.  I don't and can't have chickens, so people like us need to find other ways to crush the biochar.

In our defense, the thread IS titled "Biochar in chicken bedding and deep litter yard"

I think very few people would argue that 3"-5" chunks are ideal for anything. In a chicken coop setup, I think "small wood chip sized" (like, 1" or smaller) are probably ideal. I'd imagine these would get further broken down in the coop, then when the bedding is composted, and then applied to soil. It might not be a perfect powder by then, but it'll be small enough to spread the "microbe hotels" around pretty well. The chickens and compost process should also make sure those microbe hotels have a "no vacancy" sign in the window.

I agree. I don't think powder is ideal either.

There have been some in this thread and on this forum saying that crushing isn't helpful or they weren't willing to do it. I was clarifying what types of breaking down help  and when it would help.
John S
PDX OR

John Suavecito wrote:Crushing is not about releasing nutrients from the biochar. It's not a fertilizer.  

Not sure if that was a response to me or someone else. If someone implied that type of similarity, I missed it.

I won't speak for anyone else, but my comment was primarily just referring to the idea that I have heard repeatedly that by crushing the char you are increasing the surface area and pointing out that I don't really understand that argument.

At the same time, I do agree that there are a number of other benefits to crushing it especially for certain contexts and as you pointed out depending on the size you started with (maybe not if you're turning pine needles or something into char, but... yeah... that isn't typical. Could actually be kind of a fun project one day though lol.).


I haven't actually made a ton myself yet, but have some acreage here with trees that I'm looking to start managing differently which will hopefully include a significant biochar production once I can get everything going...  

Was actually wishing recently that I had more to use for our chickens, but alas there have been too many things going on all at once.

My comment wasn't directed at you.  I think the point of increasing the surface area is making more hotels for microbes.  Instead of mansions for a few lucky microbes, it's making zillions of tiny homes for innumerable microbes.  More microbes of different sizes will be able to access the biochar when it has more surface area, and over time, it should be distributed more widely throughout the soil.

John S
PDX OR

John Suavecito wrote:My comment wasn't directed at you.  I think the point of increasing the surface area is making more hotels for microbes.  Instead of mansions for a few lucky microbes, it's making zillions of tiny homes for innumerable microbes.  More microbes of different sizes will be able to access the biochar when it has more surface area, and over time, it should be distributed more widely throughout the soil.

John S
PDX OR

That's the thing though - I understand why you would want more surface area... and thus I see the value of things like introducing steam at the end of the production process to fracture the carbon structure further and essentially create "activated carbon".

What I was saying is that I am not convinced breaking the char into smaller pieces produces meaningfully more surface area.

However, I definitely agree that it can serve other purposes, in particular allowing it to disperse more evenly throughout the soil.

I suppose to run with your hotel analogy: Crushing the char isn't really creating more rooms in the hotel, it is taking your one massive hotel and demolishing it to build a hundred townhouses, duplexes, and little condominiums throughout the city and its suburbs... (And I would guess this probably doesn't hurt with the rest of the city's infrastructure either - you might be helping build out some additional mycelium highways for example... and throwing up some extra billboards alongside it)

Does crushing char make significantly more surface area?

Let's take an example that is typical from my biochar crushing.  

A typical piece of char straight from my burn, would be 3" x 3" x 3".  Total surface area=54 inches squared.

After crushing, with the boards (my old way) they would typically be .5" x .5" x .5".  Surface area of one crushed bit= 1.5 inches squared.
There would be 6 x 6 x 6 of them in that block, so 216.  Total surface area would be 216 x 1.5 =324.  6 times more!

Now with crushing inside bags, a typical piece is at most .25". Surface area of one crushed bit: 0.375 "
There would be 12 x 12 x 12 of them inside that original block.  
There would be 1728 of them inside  1728 x 0.375 = 648  That's 12 times more!   A significant difference in surface area.
That's just one piece of biochar.  You are making much more surface area in your biochar.

John S
PDX OR

John Suavecito wrote:Does crushing char make significantly more surface area?

Let's take an example that is typical from my biochar crushing.  

A typical piece of char straight from my burn, would be 3" x 3" x 3".  Total surface area=54 inches squared.

After crushing, with the boards (my old way) they would typically be .5" x .5" x .5".  Surface area of one crushed bit= 1.5 inches squared.
There would be 6 x 6 x 6 of them in that block, so 216.  Total surface area would be 216 x 1.5 =324.  6 times more!

Now with crushing inside bags, a typical piece is at most .25". Surface area of one crushed bit: 0.375 "
There would be 12 x 12 x 12 of them inside that original block.  
There would be 1728 of them inside  1728 x 0.375 = 648  That's 12 times more!   A significant difference in surface area.
That's just one piece of biochar.  You are making much more surface area in your biochar.

John S
PDX OR

Isn't this ignoring the porosity of the char? Treating it as a block with an external surface area only, and ignoring the internal surfaces where nutrients are absorbed and released gives a very misleading view. Biochar is much more like a sponge that a solid inert block of glass.

If a wet the surface of an inert block of glass with water it will hold a tiny amount of moisture on the surface. If I break that up into smaller pieces the surface area increases considerably, and the amount of surface water retained would scale with size of blocks as you described.

On the other hand, if you take a block of kitchen sponge it will hold a huge amount of water in it's internal pore structure. If I break that sponge down to small pieces I wouldn't expect the held water to increased much at all, because the internal structure holds the vast majority of the water, compared to the outside surfaces.

There are many good reasons to want to grind char to a smaller consistent size - easier handling, easier incorporation into mulch or soil, more even distribution through planting areas etc... but the argument about crushing to increase surface area appears to be a red herring. I would expect it to have very minimal impact on surface area and on nutrient exchange/retention.

This is an ongoing conversation.

Are you saying that the internal porosity of the biochar is exactly the same as the external porosity of the biochar? That doesn't make any sense to me at all.  The soil food web is diverse. Some of the microbes could penetrate into a chunk of biochar, some could not do it at all, and some could do it but more poorly.  Most people can not make enough biochar to optimize their soil.  If you crush it, it is dispersed more widely throughout the soil. That is a benefit of crushing.  Drainage will be way better in clay.  Retention of water and nutrients will be way better in sandier soils.   Pathways for different mycelium and other microbes can move more readily throughout the soil.  Even when I'm charging it before using it, I'm sure that it becomes charged better than if I didn't crush it.  The internal porosity of the char is nowhere near 100%.  I don't have an exact number, but it's nowhere near that.  

Sure if your organic material is already 2 cm or 1 inch across before you burn it, crushing it may not help as much.   If you have animals that will crush it, great.  Not everyone has that.   Biochar is not a sponge.  It's more like a clod of earth than a piece of glass or a sponge.  There would be some internal porosity, but not approaching 100%.  Besides, my homemade stuff is activated with steam.

Refusing to consider the value of crushing it doesn't make it worthless.

John S
PDX OR

John Suavecito wrote:Biochar is not a sponge.  It's more like a clod of earth than a piece of glass or a sponge.  There would be some internal porosity, but not approaching 100%.  Besides, my homemade stuff is activated with steam.

Refusing to consider the value of crushing it doesn't make it worthless.

John S
PDX OR

So your personal belief is that biochar has negligible internal porosity? That does explain the difference of view here.

The porosity of biochar is extensively studied by much better scientists than myself, and is one of the key figures considered when people are trying to make "good" biochar - specifically because the pore structure is believed to be key to nutrient exchange and storage. It acts very very much like the structure of a sponge on a molecular scale, and all of those internal surfaces are sites where nutrients can lightly bind and so be protected from leeching from the soil.

Scanning electron microscope images of biochar pore structure



This pore structure is on the scale of micrometers, beyond what can be observed by the naked eye. Those internal pore surfaces have vastly greater total than the external surface area, and total surface area is the key factor for nutrient storage and exchange.

I didn't say negligible.  That's not what I said, and I don't appreciate it.  

I said not 100%.  I appreciate it when I am quoted correctly.  A clod of earth has porosity too.  

As I said, many materials can go into the internal pores, but many can not go through biochar into the internal pores.  

Crushing it increases the types that can and are likely to enter the biochar.

John S
PDX OR

I am no longer interested in this argument.  It doesn't feel productive about sharing points of view.   I have agreed with you on many points.  You have agreed with many of my points.  You say that my mathematical calculation of surface area is flawed when showing that it does have more surface area, but the same calculation done by others is fine if the goal is to prove that there is no increase in surface area.  I don't think that makes sense.  

I would prefer that people go back to sharing ideas about biochar.  I don't want to annoy others on this forum who are actually experimenting and trying to figure out how this works, and to share it with others.   I'm done with this argument.

John S
PDX OR

I think it's an important thing to consider for one's context and biochar use

My personal context, production style and use:

I live on sandy soils with stones throughout, our climate gives brutal winters and hit dry growing seasons with most moisture on the shoulders when plants and microbes are less happy or active.

I produce in a "cone pit " that is really more of a trench, I break my material up with a shovel as it burns to facilitate better coal formation and no airflow in the core of the pit, then drench when finished.

I use the char in bedding, any stinky spots I have, to "thin out" seed mixes and make broadcasting cover more ground ahead of animal impact. and largely as a carbon source for my compost collection program, based on 5gal buckets

I don't crush for a couple of reasons:
I don't desire to risk breathing it in.
Dust would largely get blown away and collect unevenly where the wind distributes it, this still happens with chunks a bit.
I don't want to do the extra work.
My current method replaces need foe wood chipping equipment and I wouldn't want to bother with equipment for biochar.

And from my understanding, Crushed char increases surface area for microbes.
mathematically this seems factual.
though increase would not be linear as it would with non porous materials and I don't care to calculate it.
However I do believe that larger chunks of sponges is an accurate analogy, I have heard that chunky char holds moisture better and that is a large goal of mine because more consistent moisture will acc9mplish biological goals in my region more effectively than a simple increase in surface area would

I have screened fines for animal supplements, and would consider doing so as a means of acting as a carrier dust for mychorizal innoculants, crushed char would likely be a good option for these means also

I've tried using bio char/ compost mix without crushing first and it worked fairly good, I found roots growing right through the chunks of bio char. The next season I tried crushing some biochar sifting the compost more, and had even better results. Now what I like doing is crushing 80-90% of the bio  char I'm gonna use and leaving the rest as medium size chunks that roots can penetrate. This may get adjusted in the future as I try things out.

Yes, my chunks are just way too big straight out of the burn to avoid crushing: 2-5" in diameter.   I crush them somewhat, but I have to remove the bags from the driveway after a bit because they will get too much like powder.  I don't like the dust either.  Optimal for me is from like a centimeter in diameter to an inch in diameter.  We get very dry in the summer.   I do spray water on the biochar in the summer to keep the dust down if I'm not ready to inoculate/charge it yet.  I use liquid inoculant so there is no dust after charging.   Then I cover it with mulch when it's in the ground so it won't dry out there either.

John S
PDX OR

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This is an interesting topic which could be discussed by asking gentle questions and accepting that there are many right answers depending on so many nuanced factors - soil type, material availability, goals, time

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