Biochar is a special kind of charcoal that seems to have many benefits as a soil amendment. It holds water, acts like a fertilizer and grows bigger plants. While doing all this it is also eco-friendly and sequesters carbon in the soil for many thousands of years. Sounds like a win-win-win.
What is biochar? Are the claimed benefits real? Should gardeners be using this product to amend their soil? Let’s check it out.
What is Biochar?
Everyone agrees it is charcoal made from pyrolyzed plant-based organic matter including such things as manure. The term biochar is quite new and was coined by Peter Read in 2005.
Several sources including the UC Davis biochar database and Wikipedia say it is charcoal that is primarily used for soil amendment and not for heating. That is interesting, but does not really describe what it is.
It is created in a low, or no, oxygen environment so that it maintains its fine grained structure.
The International Biochar Initiative says it’s produced at low temperatures and then goes on to define this as <700°C. The UK Biochar Research Center says it should be made above 250°C in a zero oxygen environment. “In general higher pyrolysis temperatures mean a smaller amount of char, but containing a greater proportion of highly stable carbon”. Others say it needs high temperatures, over 500°C.
Biochar vs Charcoal
We have all seen charcoal and maybe even used it in a barbecue (real charcoal, not the briquettes). How does this differ from the new biochar?
After much searching all I can determine is that the end use determines the name of the product. Some sources hint at the fact that the manufacturing processes are slightly different to produce products with different characteristics, but nobody gives details.
A report by the Illinois Prairie Research Institute says Biochar is not a new product, just a new name for material that is used to amend soil. In fact it says biochar covers a wide range of products including char, charcoal and soot.
This certainly would explain why nobody seems to be able to describe the difference between charcoal and biochar. It is charcoal when used for burning, and biochar when used to amend the soil.
Biochar Varies a Lot
Biochar is a variable product and its chemical and physical characteristics depend very much on the input ingredients, the process used to pyrolize it ( temperature and length of heating) and any chemical treatment after production.
This makes it difficult to make any definitive statements about its use.
Claims for Biochar
The claims made for biochar include:
- increase yields
- increase fertilizer efficiency
- remove pollutants and pesticides
- mitigate climate change
- increase soil moisture
- increase soil pH
- increase soil microbe populations
- increase cation exchange of soil
Most of the studies that have led to these claims have been done in the lab and very few field tests exist.
Both charcoal and biochar absorb chemicals. They do have negatively charged sites which increases the CEC (cation exchange capacity) but if they absorb pesticides or nutrients then this can be detrimental to plants since it makes these products less effective. We also know that activated charcoal, which is used to scrub chemicals, gets saturated and needs to be replaced. I would expect that Biochar in soil will also become less effective over time, but nobody mentions this. There are no long term studies.
Biochar does increase the pH of soil and holds more water, neither of which are benefits in alkaline clay soil. It does increase microbe populations.
One review of current studies reported, ” In biochar studies reviewed, half reported an increase in plant yield after adding black carbon or biochar, while 20% noted decreases in plant yield, and 30% reported no difference in plant yield from the addition of biochar.”
A review of a large number of studies concluded that the application of biochar can be both positive or negative depending on the parameter being measured, and that it is site specific. “This review has indicated many benefits, complexities and effects of biochar; however, more research is needed”
Field studies are mixed on the yield issue with some showing an increase and others showing a decrease. Some studies show positive results when used with fertilize, or on acidic, low fertility, soils.
A four year study looking at growing vegetables in a simulated back yard garden, at three different sites, found mixed results; some increases in yield and some decreases in yield.
It is important to keep in mind that the characteristics of Biochar vary a lot and soil plays a key role in determining how it might affect yield. It is therefore not surprising to see mixed yield results.
It is clearly not the cure-all bullet some claim it to be.
How Does Biochar Affect Microbes?
The effect depends on the type of soil and crops. Wood-derived biochar can have short term positive effects but amendments can also reduce microbial biomass. Biochar can increase pH resulting in a modified community, which may not be beneficial.
Charging Biochar
Many sources recommend that you charge biochar before using it. This can be done by mixing the biochar with compost, or just adding it right into a compost pile and composting the whole thing. You can also soak it in manure tea or just add some synthetic fertilizer to the biochar.
I am not surprised charged biochar works better. All of the active negative sites on the biochar will now be saturated with nutrients. When it is added to soil, it can add nutrients to the soil and make them available to plants. On the flip side, un-charged biochar is like a magnet. When added to soil it sucks nutrients away from plants, at least for a short period of time. This may explain why some studies show a decrease in plant productivity when the soil is amended with biochar.
Are the reported increased yields due to the added fertilizer?
Does Biochar Sequester Carbon
Even if biochar does not increase plant growth, it is believed to be a really good solution to our CO2 problem. If plant material is left to compost, it produces CO2. If it can be turned into biochar, and then added to soil, it will essentially bury our CO2 problem.
The efficiency of this all depends on how long biochar remains in its charcoal form. People have suggested it is very stable and will last thousands of years but there is almost no science to prove this. A report from the Earth Island Institute says, “Field trails proved rare; only five such studies were found, which between them tested biochar on 11 different combinations of soil and vegetation. In only three cases did biochar result in any additional carbon sequestration. In most cases, there was either no measurable difference in soil carbon, or even a reduction in soil carbon. These results from short-term studies —none spanned more than four years — fly in the face of repeated claims that biochar will sequester carbon in soils for tens, hundreds or even thousands of years.”
A recent peer-reviewed study revealed that 72% of the carbon was lost in the first 20-30 years. “There is little basis for confidence that charcoal will retain carbon in soils“.
There are also environmental costs for collecting the raw material, creating the biochar and redistributing it back to soil. Maybe the whole process is not ecofriendly?
Organic Matter or Biochar
One of the big benefits of biochar is its ability to hold onto positively charged nutrient cations (calcium, potassium, magnesium, etc). Clay and organic matter do the same thing. The organic matter turns into humus which sequesters carbon long term, but maybe not as long as charcoal.
One has to wonder if it might be better to just add the organic matter to soil and let nature take care of things?
Biochar as a Byproduct
Most producers of commercial biochar are more interested in producing biofuels and biochar is a waste product for this industry. Using it for soil amendment in this case may be eco-friendly.
Can You make Biochar at Home?
Some sources say you can’t make it at home because you can’t get things hot enough and control oxygen well enough. It is clear that simply burning things in a fire or in a pit won’t make good biochar, and if it is not made properly it can release harmful gases such as methane and carbon monoxide.
Others have designed special DIY stoves that seem to make reasonable biochar, although the process is not tightly controlled. Campfires can reach 1,100 °C, so a properly built system could reach the temperatures needed. Stoves built with two chambers, one for burning to make heat and one for making the charcoal in low oxygen conditions might work. With the right system you can make biochar at home.
Since there is no clear definition of what biochar is, I guess it is hard to say you can’t make it at home. But keep two things in mind:
- Just because you make some black charcoal does not mean it will have any of the properties reported for biochar. Its properties depend on how it is made.
- If it is not made properly you will be creating more pollution than you save.
It really is better not to make your own.
Biochar in a Potting Mix
Biochar has been shown to inhibit seed germination so it should not be used in a seedling mix.
It can be used to replace some of the peat moss in soilless mixes where the increase in pH counterbalances the acidic nature of peat moss.
Should Gardeners Use Biochar?
Biochar has been shown to have some benefits in the garden and it might be a good amendment for soilless potting mixes, but here is the problem.
Biochar is not one product. It can be made from many different input ingredients, in many different ways. The result of each process is a different product with its own special characteristics. There are no standards so you can’t pick up a bag and say, “this is the one that produces good results in my soil type”.
You are left with buying a bag of something and hoping it works.
You have the same issue with buying compost – who knows what is really in the bag?
But there is one big difference between compost and biochar. Unlike biochar, compost decomposes in a few years. A bad batch of compost is a short term problem. Biochar may not last a thousand years, but it certainly lasts a lifetime. What do you do if you add a bad batch to your soil?
Many studies have shown that too much biochar is harmful to plants and soil. You can’t correct this problem without removing the soil.
It may be more beneficial in acidic soil where the increase in pH is desirable. It has also been shown useful in reducing compaction in lawns and poorly drained soil.
If you want to try it, start small and use some test areas. Keep the amounts small. Document the product you use so you can buy the same product again.
I think I will sit on the sidelines and stay away from it, for now. Compost seems to offer most of the same benefits without the downside.
Biochar or charcoal can slow down decomposition of organic matter or fertilizer. It would not be beneficial to apply them in temperate climate as which fungus and bacteria will release less nutrients due to slowed down decomposing matters. It is beneficial to add in subtropical or tropical climates as they have problems with organic matters decompose too fast. That is why scientists found terra preta in Amazon basin where plants grow better.
How does biochar slow down decomposition of organic matter?
It is not going to slow down the decomposition of fertilizer, since fertilizer is already in an ionic nutrient form.
My understanding is that when produced properly in a near oxygen free environment the resulting char or charcoal is basically carbon with minimal contaminates remaining and virtually no Ash so ends up the same ie carbon regardless of what it started out as therefore pure char should not vary as you suggested.
I did not suggest this – I am simply reporting what the experts in this field say.
One of the principle benefits of biochar (at least in theory) is that it provides massive surface areas for growth and retention of microorganisms. It also can hold moisture. These benefits are directly related to the physical characteristics of the biochar. With complete pyrolosis, biochar is a carbon skeleton of the starting material. The physical characteristics of that skeleton is highly dependent on the physical characteristics of the starting material. However, there may also be chemical differences too, IF the ash residues are not completely removed. Again, the physical properties of the biochar can affect how readily those ash residues are separated from the biochar product. I concur with author’s original statement- biochar quality is highly variable.
Sorry, I know this is an old article…
When I was researching biochar, the main specifications seemed to be high surface area carbon structure.
Different preparations would somewhat affect that and of course certain methods more “ideal” for whatever circumstance.
So that’s pretty the only way I look at it.
Anyway, I’ve used some local commercial biochar (with added phosphorus) and same char manually made. Pretty crude, just used soil I was going to combine it with anyway and water to “temper” the fire and lower oxygen somewhat.
I already have dark, very heavy clay soil as a base seemingly fairly high in potassium and magnesium, BUT….adding char/ash from around 5 – 20% seemed to offer benefits.
Essentially, as a crude example, I’d have the soil and char prepared, then I might mix in some fresh-ish stuff, compost, whatever fertilizer I deem necessary (such as calcitic lime coz of the clay) throw molasses, sugars, maybe some milk and random stuff at it. Then I’d just mix that, let it age for…maybe even only a few days and use it to great effect, so far.
Cheers.
It seems that ‘black soil’ has also been used in Africa, and other places, to ‘enrich’ soil. As I understand it, an early explorer found a large population, cities et al when exploring the Amazon, and others who came many decades later, found no one. Agronomists in the modern era determined that tropical soils are/were too poor to support agriculture that could support a large population… the first guy must have been ‘mistaken’. Then, recently, signs of former ‘cities’, etc have been found, and terra preta also ‘discovered’, which could explain how they grew a lot of food in one location over a long period (before alien diseases taking them out).
This refers to normally very poor tropical soils, where ‘compost’ disappears almost instantly in the hot, moist, biologically hyper-active environment. In our cooler temperate region, compost can last for… a couple of years? (That leaf pile shrinks dramatically!) So, I think terra preta might help in my (maritime WA US) very sandy, tending acidic, soil, but probably not as dramatically as it does down south. (Although, my soil becomes very dry in our long warm summers.) BTW, I don’t think questions re: biochar can be answered by standard science … the ‘natural’… er, real world is too multi-dimensional.
Charcoal used as a filter removes undesirable particulates from air or water. It is proven, it works very well. that is why it has been used for that purpose for a very long time. In soil it works the same only the result is nutrients, bacteria, and water are retained where the plants can put them to good use. In my mind, that’s a win no matter what process is used to make it, or what you call it.
Only if it actually works.
Thank you for your review of the material. I still can’t get my mind of what is biochar, or charcoal. I don’t know why it would be better or different than coal or coke. Coal comes from plants just like the raw material for biochar or charcoal, except that it was heated and compressed by natural forces. Coke is coal heated in a oxygen free environment, the same way as biochar and charcoal is made. So is it really different?
The other thing I can’t get my mind around is why do all the effort to make biochar. First you have the gather the feed stock along with the material to fire the process. You throw it in a specially made chamber and heat everything up. Then you let is cool down. Then you have to break it up. Then you need to charge it with something. Finally after all that you need to till it into the garden. Whew! What a lot of work.
Alternatively, I could grow a cover crop, mulch it, add Calphos, kelp meal, and other mineral supplements. I would then let microbes, earthworms, pill bugs, and whatever incorporate it into the soil. It will eventually become humus and maybe last 20 years. Each year adding more cover crop etc., more humus. Seems like a lot less work to do that.
Some good points. Growing stuff is also a good solution. The idea of using biochar is that it is a very long term solution to sequestering carbon. Growing things is only short term, unless people are around to do it for a long time.
I think coal does not have the same nutrient absorbing characteristics as biochar – but have not looked into it.
I’ve seen some references to research regarding Terra Pretta soils in the Amazon River Basin over the years which incorporate a variety of material inputs including charcol, and was the basis of early indigenous agriculture there. I’ve presumed that the biochar trend was partly inspired by this. I’ve been warned by 2 soils specialists that Biochar is not a magic bullet for me and my gritty soil. Both primarily criticize the point you brought up re:nutrient draw or lock up. I was told locally available organics and mineral products are more predictable and safer, but those Loma Pretta soils, carbon sequestration etc. still grab my interest.
A combination of the ‘placebo’ effect and the ‘attention’ effect might account for most of the positive value. I add a certain amount of charcoal from the Bar-B-Que because I think it provides another growth medium for various soil biota. I also add small amounts of sand, clay, peat, manure, and compost it all in my worm composter.
I’m hoping that providing various growth media will add to soil fertility reasoning that soil that is fertile for a wide variety of biota will also be fertile for my veggies and the larger animals, especially birds, that feed on soil insects.
We are about to start up a production of bamboo biochar and as the process of building the entire factory is still in a stage where we can correct and modify…. please let me know what do you think ?
What best suggestions you may supply in terms of what kind of bamboo biochar we should produce to make sure we render a good service to the community and that it will be a success. We are also looking for experts to add to our team , so anyone wanting to join or at least have an interview is highly appreciated and welcome. Thanks Roberto
I am inclined to think that the idea of “real” biochar is more of an administrative designation than one of “scientific designation”. While most of the biochar you find follows various processes of manufacture, the structural and chemical characteristics that lend benefit to specific agricultural or soil/water balance functions remain the same.
Water and runoff absorption, as well as horticulture use attributes can be easily compared to other products used for the same purposes.
If you are purchasing biochar for agriculture or remediation, look for a seller that specifies the qualities you seek. Ph is easily measured, and if sold as a soil amendment or composting material, most states require registration and labeling of NPK.
Absorbing surface area can be measured with water displacement (in a post aqua-phobic state). After measuring, amendments can be adequately calculated for entry or for runoff/water management purposes.
None of this is recorded on the label of most biochar sold, especially online.
Add in live fungus/bacteria inoculation and it is easy to see that the market for biochar does have vast room to expand, but the end user education is being neglected at the expense of customer confidence, both through a lack of information, and the end consequences of its use under these conditions.
The term “organic” still has an inconstancy in terminology as well. Organic in the USA and Canada are different, with Canada opting out of the certification of crops grown with sodium nitrate fertilizer, the US allows it, in the USA no antibiotics for livestock – under certain conditions Canada allows it. Canada has land availability rules for livestock, the US does not, your hydro hemp is organic in the US, but not in Canada. Let’s not talk about 100% organic, organic, made with organic, or the terribly misused term “natural”.
I readily endorse biochar use, but like any soil remedy or amendment, it must be made to match the soil type and purpose. Most people’s eyes glaze over when you ask them if they know their hardiness zone and soil type… That’s why they go ahead and spray “Natural” Garden bottled Roundup on their veggies, not knowing it is isopropylamine salt of glyphosate.