What is Biochar?

Estimates for the amount of carbon that could be sequestered by biochar range from 1 gigaton to 35 gigatons per year.

There is an increasing awareness of biochar among the agricultural community and beyond, but what is it? David Butler, head of sustainability at Alltech, joins Ag Future to discuss the history of this porous piece of carbon, its application in agriculture and how it's now being used in products ranging from asphalt to jet fuel.

The following is an edited transcript of the Ag Future podcast episode with David Butler hosted by Tom Martin. Click below to hear the full audio or listen to the episode on Apple Podcasts or Spotify.

Tom Martin:            I’m Tom Martin, and I have some questions. What is biochar? How is it made? How is it used in agriculture? And how can it help with climate change?

All questions for David Butler, head of sustainability at Alltech. Thanks for joining us, David.

David Butler:           Thanks for having me, Tom.

Tom Martin:            So, let’s begin with those basic questions — and first, what is biochar, and how is it made?

David Butler:            Well, biochar is very similar to charcoal, really, but charcoal is specifically used as a fuel and biochar is not. It has lots of other uses. But it’s biomass that has been baked at a really high temperature in the absence of oxygen, so it’s essentially kind of crystallized carbon. All the volatiles are driven off and you’re left with this very, very porous piece of carbon.

Tom Martin:            Any idea who had the “eureka” (moment), for whom the light bulb went off, (or) how the process was discovered?

David Butler:            Well, I think people have been making charcoal for thousands of years, probably, as a fuel. But also, there are a lot of places in the world — especially in the Amazon — where you can find that biochar was used as a soil amendment.

                                And it might have been an accidental discovery. They would kind of bury and burn their waste, so they would be burning waste without oxygen, because they were burying it. And you find soils there that are very rich and black, even hundreds and/or thousands of years later, and that’s called terra preta soil, black soil.

                                And that’s, really, how they fed a very large population there: by enhancing the very poor Amazon soils with biochar.

Tom Martin:            So, they burned their trash and then buried it, and it continued to burn. Is it possible for that to happen without so much oxygen?

David Butler:           Yeah. That’s a really good question. So, it doesn’t actually burn in a lack-of-oxygen environment; it undergoes a process called pyrolysis. And what that involves is kind of breaking down this organic material, driving off the volatiles and reducing it, pretty much, to carbon and minerals. So, it’s not burning, because burning does require oxygen, and at the end of it, you’re just left with carbon dioxide and ash.

Tom Martin:            Huh. So, when you dig it up, what does it look like? What are its properties? What can it do?

David Butler:            Well, it really looks just like charcoal. And you know, there could — you could have relatively large pieces, or it could be almost, you know, microscopic size.

                                 And if you look at it under a microscope, you’ll see that it’s very, very porous. And if you think back to high school, maybe you looked at plant cells under a microscope, right? And so, you know what that looks like. There are all these kinds of spaces that are — they’re mostly liquid in the middle of the cell, and then you have the cell walls.

                                Well, you can imagine, if you baked that at hundreds of degrees, you would drive off all of those, all of those liquids and volatile compounds, and you would be left with kind of the skeleton of the plant matter — and that’s really a major, important property of biochar, is that it’s so porous, because it’s this organic-matter kind of crystal carbon skeleton.

                                And in addition to being very porous, or because it’s very porous, it has a huge surface area. So, it can hold a lot of water, but it can also hold nutrients like nitrogen, calcium, potassium and phosphorous. It can even hold toxic metals and kind of bind those up.

                                And it’s also a great home for microbes. It’s kind of like a little apartment complex for microbes.

Tom Martin:            [laughs] So, lots of implications there. Let’s look at a big one here.

According to the International Energy Agency, global warming could be kept to 1.8 degrees Celsius above pre-industrial levels if all the pledges and the promises that were made at that recent summit in Glasgow are kept. Scientists have said that warming needs to be kept at 1.5 degrees or below that to avoid the most disastrous climate consequences, but 1.8 degrees is still big news, given that, right now, we’re actually careening toward a 2.7-degree rise.

                                So, to what extent can biochar play a role in helping us get a handle on that rate of increase in (global) warming?


David Butler:           Yeah. That’s a really good question, Tom. And I think that a lot of people are trying to figure that out right now, because even though biochar is a very, very old technology, the biochar industry is relatively new and growing, and there are a lot of exciting things happening with the industry, but it’s still in its infancy, really. It’s still kind of tiny.

                                So, estimates for the amount of carbon that could be sequestered by biochar range from 1 gigaton to 35 gigatons per year. And that’s a huge range.

Tom Martin:            Yeah. What about agriculture? There are indications that it’s already being used in farming; is that correct?

David Butler:            Yes. And you know, it’s been used for a long time by farmers, and I think it’s getting more awareness now, and it’s starting to spread. And one of the fascinating things about biochar is that, because of its properties, it has many, many uses. So, there are a lot of ways to use it in agriculture.

Tom Martin:            Well, let’s explore that a little bit. When biochar is worked into the soil, let’s say, what are the benefits to the farmers?

David Butler:            Well, I mentioned that it holds water and nutrients, and it also is a place for microbes to live; it’s like a little ecosystem for microbes. So, all of those things are beneficial for the soil.

                                 And, first off, if we talk about water, if you have all these little pieces of biochar in the soil that kind of act like little sponges, and they hold water, which means that under times of drought, you have all of the water that’s been saved in the biochar. But also, when it rains very hard in an extreme weather event, then the soil can hold more water, so there’s less runoff and there’s less erosion.

                                So, it really helps with resilience on the farm, especially as we’re seeing more weather extremes due to climate change.

Tom Martin:            We hear so much about these large lagoons, especially in swine production. And so, what about manure management? How can biochar make a difference there?

David Butler:           Well, there’s kind of two ways to look at that.

For one thing, you can take the manure and convert the solids from the manure into biochar. So, that’s huge, because it allows you to stabilize all the carbon and the nutrients in that, in those manure solids, and you’re reducing the volume of them, and so you have a lot less material to deal with.

                                 And once you’ve converted it to biochar, of course, there’s no odor — it’s not going to leech any nutrients — and you end up with this very valuable product as a result: you have the biochar. And you can take that biochar and put it on your manure lagoon. You can use it in your bedding for cows or — you can use it in your bedding for cows, and that helps keep them dry and helps with hoof health and things like that.

And then, you can also take it and spread it on the fields. And it’s great to, you know, mix it in with the liquid portion of the manure that’s going to be injected into the fields, because it helps to absorb methane and hydrogen sulfide and, most importantly, ammonia — it keeps that manure from off-gassing ammonia, which means that you’re keeping the nitrogen in the manure, which makes it a better fertilizer, which means you don’t have to use as much synthetic fertilizer.

Tom Martin:            It sounds as though we’ve finally found a way to literally make a silk purse out of sow’s ear.

David Butler:           Yeah. I think that’s a good analogy.

Tom Martin:            Well, there seems to be a lot of excitement about biochar in the dairy industry. What’s driving that enthusiasm?

David Butler:            Well, I think one really exciting thing (is that) there are some people working on projects where they build small biochar kilns on the dairy, and they take the manure solids and they convert those to biochar. And in the process, they get renewable energy, because when you heat the manure, you also get synthetic natural gas. You can get bio-oils, and then you can take those and burn them to make renewable electricity, or you can convert them to diesel fuel or natural gas for heating or for transportation fuel.

                                There are even some companies working on a biochar process to produce green jet fuel.

Tom Martin:            I’m just sitting here listening to that, David, and thinking about the broad implications of what I’m hearing, and it sounds to me as though we’re talking about the possibility of an alternative to fossil fuels and a renewable energy source that could be in abundance and could be quite helpful in approaching this whole climate change issue.

David Butler:            Yeah. It’s certainly a very exciting piece of the puzzle. You know, I don’t know that it’s going to solve all of our problems, but it’s a technology that’s, you know, it’s available right now, and we just need to scale it up.

                                And in sustainability, people love to talk about things that are a win-win. Well, biochar is kind of win-win-win-win. There are so many benefits to it, and you’re getting renewable energy as you produce it.

Tom Martin:            Once you’ve created biochar on the dairy farm, are there other ways to use it?

David Butler:            Yeah. You know, so I mentioned that you can add it back to the manure, and of course, you can use it as a bedding material for dairy cows, but there are also people (who) use it as a feed supplement for their dairy cows, and that’s not currently allowed in most of the U.S. There probably needs to be a lot more research on that, but there are many countries where that’s being done, and some people report good benefits from that. And I’ve read that that can even reduce methane emissions from cows. I think, you know, there are a lot of kind of anecdotal solutions that claim to reduce methane emissions from cows, so there needs to be a lot of research done on that before we can really hang any hopes and dreams on that.

Tom Martin:            You touched on this earlier, but let’s explore this question for just a moment, because it tends to be kind of overwhelmed by all the discussion around climate change, but it’s equally as important to our well-being, and that’s water. How does the use of biochar improve water quality?

David Butler:            Yeah. That’s a really great question, because agriculture does have or can have an impact on water quality. So, we can look at that in two different ways.

When we talk about, you know, a field of crop land, then you want to make sure that your fertilizer is not running off every time it rains and ending up in the stream. And you know, if that happens on a large scale, then you can get algae blooms in streams but especially in lakes or even in estuaries in the ocean. So, it’s very important to keep those nutrients on the field and not allow them to escape into the waterways. And it also economically makes sense to keep your fertilizer on the field.

                                 So, biochar — because it holds nutrients, it prevents them from being leeched and washed away in heavy rain. And it holds them in such a way that the plant is able to extract the nutrients from biochar when they need it. So, you don’t have to use as much fertilizer, and that’s an important thing, too, because synthetic fertilizer has a very high carbon footprint. It takes a lot of energy to make fertilizer.

Tom Martin:            That is a pretty big implication, because runoff is pretty pervasive in so many ways.

David Butler:           Yeah.

Tom Martin:            We’ve talked about its agricultural applications, but can biochar be used to make other useful things?

David Butler:            Yeah, absolutely. And I think, (for) the biochar industry, a few years ago, the biggest focus was on agriculture, but it can be expensive to get biochar out onto a large-scale farm and work it into the soil. And so, there are other industries where it can be a lot cheaper to use biochar as an alternative product.

So, it can be used as an ingredient in asphalt. It can replace a certain amount of the sand or portland cement in concrete — and both of those substances have a really high carbon footprint. So, as those industries try to reduce their greenhouse gas emissions, they would love to take a carbon-positive portion of their product and replace it with a carbon-negative ingredient.

                                 It can also be used in plastics, cosmetics — just lots and lots of different products. But you know, the potential to put it in our roadways is huge. And the nice thing about that is if you’re using it in construction materials, then you can use biochar that’s maybe not of the same quality that you would need if you’re going to use it as a soil amendment. So, you can make biochar from sewage sludge, for instance — and that may have a lot of contaminants in it; you probably don’t want to put that in the soil.

Tom Martin:            Well, this seems, David, like one of those moments when something has been discovered that has so many applications, and important ones, in terms of our environment, our well-being. Do you feel that way? Do you feel like we’re on the — at the beginning of something really important here?

David Butler:            Yeah, I do. I think it’s very, very exciting, and I think that the biochar industry is really going to start to accelerate.

One reason for that is that, last year, the Intergovernmental Panel on Climate Change came out with a report saying, you know, “Here are some of the methods that we can use to draw carbon out of the atmosphere,” and biochar was listed as one of those. So, it provided legitimacy to this growing industry. And now, because of that, biochar is being added as a method to a lot of different carbon-offset markets.

Tom Martin:            So, it’s an alien term at the moment. Do you see the day when we’re going to be talking about biochar as something just normal in life?

David Butler:            Yeah, I think so. And another good indication that that’s coming is that Microsoft and Shopify recently included biochar in their net-zero plan. They’re buying biochar credits already.

Tom Martin:           How about that. Well, let’s keep following this.

David Butler:           All right.

Tom Martin:            All right. That’s David Butler, head of sustainability at Alltech. Thanks for joining us, David.

David Butler:           Yeah. Thank you, Tom.