The facts on biochar

Those of you who are highly knowledgeable about using biochar, I would appreciate you, addressing professor David Laird’s of Iowa State University ideas regarding its use.

I am especially interested in responses to his idea that to be affective, tons per acre are needed…not pounds per acre.

As the article says, biochar is not magic.

To put things in perspective:

“An acre furrow slice is the volume of soil in an acre of topsoil 6-7 inches deep. The estimated average weight of soil in an acre furrow slice is 2,000,000 lbs (1,000 tons).”

So ten tons per acre is 1%.

Robert, I’m not following you on the value of calculating the percentage. Could you explain a little more why that calculation is important? Or what is the significance of that percentage?

Hi AFHGlen,

I believe the signification of the calculation Robert Fairchild posted is along these lines:

It takes a lot of something (a soil amendment) to change the properties of a soil.

I recall such a calculation in the context of trying to change a soils properties. For example say you have a very sandy soil and you want to increase the clay content, perhaps to increase water holding capacity or CEC… it would take AN ENOURMOUS amount of clay to change it - and would likely not be economical.

The above really assumes you’re doing it on a large area (arable cropping etc) if you are talking about a couple square meters of garden or garden beds or a green house - it suddenly becomes more do-able.

I felt the gist of David Laird’s article was that he was responding to a post/ or article he’d seen about biochar where he was basically saying that based on his (extensive) research and experience he felt the person who had written the article was over selling biochar… and that (getting to your question) in the case of having an effect on areas such as acres of land… pounds isn’t going to be enough, one needs to apply tons.

I will prefix this by saying I do not consider myself “highly knowledgeable about using biochar”. I have worked in agronomy. When I googled “quantity of biochar needed to apply to be affective”
I found the following calculator:

The results of which go along with what David Laird and Robert Fairchild are saying

In the second article which came up called " Method of biochar application affects growth, yield and nutrient uptake of cowpea" they were using 5 tons / ha. (4532 pounds / acre).

The third article which came up was this one which states that the most suitable application rate of biochar was 10.1−20 t ha−1 or 2.01–4 %.

Anyways - as I said I am not a biochar expert, I did find (from superficial research) results that go along with David Lairds - basically being that one needs to apply lots of it (ton, and not pounds) .

One could look up “microdosing biochar” - I know people do that with fertilizers … but I feel its a different kettle of fish. I think you’ll find that to correct micronutrient deficiencies one could apply 10 - 40 pounds of a micronurtrient and (if it is limiting crop production) see a noticeable difference. Given that bio char is instead used as a soil amendment to "improve the key soil biological properties, mainly owing to their alkaline pH and structure, improving the soil porosity, aggregation, and water-holding capacity that promotes soil nutrient bioavailability and microbial growth (google search of: biochar as a soil amendment). I wouldn’t bother using small amounts of it on an acre scale…

While I’m not experienced with biochar - I’ve used wood ash a lot which often contains chunks of charcoal. Where I am - with really sandy soils, low OM and low K and P levels… being a bit acidic, and where wood ash is not valued and cheap. I’ve been using it and encourage others to use it as I’ve seen it give really good results. I would generally apply it at 3 ton/ha… and yeah… if I had a few pounds of it only (a couple sacks)… I’d likely put it on a few rows of crops (a strip) but in the same concentration in the hope that a difference would be very visible to the naked eye and encourage people to use it on a broader scale. If it was wood ash I’d encourage people to put it at 300grams per square meter…

Based on what I just read on biochar - I’d go for around 500g - 1 kg per square meter. (1.6 - 3.2 ounces / square foot … if I did my math right.

Do any of you make the stuff - how different from charcoal is it? why not just dump organic matter on your land - or leave crop residues or use wood ash or other cheap things people don’t want? If one has the choice to combust organic material (thorn branches etc) is one advantage of making biochar rather than just burning it and making ash that you can get more carbon into your fields?

Anyways - that’s enough from me - can we hear from someone experienced in using biochar?

AFHGlen, have you used biochar much? If you have please share what you know.

We have not been using nor making biochar but planning to begin very shortly. Like many of you, we do our composting by using the material as mulch around the plants. In the past when we could get extra amounts of wood ashes from local sources, we added those also as mulch around the plants. But we have switched, and now we add the wood ashes to our bokashi mix, hoping the micro organisms working in the bokashi will help break down the wood ashes. We also add volcanic rock dust to the bokashi mix also hoping the micro organisms will help to break it down releasing the minerals.

We are beginning to experiment making our own biochar using low-cost sawdust. Technically speaking, we are not using biochar. We are simply using small particle charcoal made with sawdust and by adding it to our bokashi process, the charcoal will get “charged”…filled with micro organisms and thus become biochar. In as much as we make 30 of the 55 gallon barrels of bokashi each month, that is a significant part of our fertilization program.

I initially asked the question beginning this thread because the professor contradicted what almost organic farmers profess… that even a few pounds of biochar per acre can make a difference. I am not sure what to believe but inasmuch as a large portion of the organic farming world believe in using biochar in relatively small amounts and inasmuch as it is not expensive in time or money, I’m willing to try it to see what happens.

I am interested in hearing from those with experience.

It seems to me one way to explain the discrepancy between the professor who says tons rather than pounds are needed per acre is the professor is working with degraded soil that has used artificial fertilizer for years and has very low organic matter. So, adding many tons of bio char to the soil, the biochar is functioning as organic matter…rather than as biochar.

With the addition of multiple tons of biochar, the organic matter is increased from near 0% to 1%, he sees a positive result. But on organic farms that probably have 6% or more organic matter in the soil, adding a small amount of biochar, it would function in a totally different capacity than organic matter and thus a small amount could have positive results.

Hi Glen,

Wow, you’re making 30 barrels of bokashi a month. That’s quite the operation. At 100 kg each that’s 3 tons a month. I imagine that gives you a work out!

I do feel I should mention in response to what you wrote about adding ashes to the bokashi in the hope that the bokashi will break them down, that if you look into it I think you’ll find that the vast majority of nutrients in wood ash are already water soluble.

Furthermore, and maybe you are already aware of this but ash is very alkaline and is so anti bacterial, anti-microbe, anti fungal that it is recommended by WHO to be used as an alternative to soap when soap is lacking

To put it in other words. If you add too much ash, I’d be worried that it could raise the pH so much that you’d lose a lot of the biological life in the your compost that you’re wanting to add to your soils.

Anyhow, you might already be aware of that and only be adding ash in small quantities or be keeping an eye on the pH.

All the best with it!

Regarding the “biochar” you are making. You post seems to imply that biochar gets its name from when charcoal gets “charged” with microorganisms.

I may be wrong but I don’t think that is actually the case… I believe biochar gets the “bio” in its name because its made from biomass, not because it is then “charged” with biological life in a compost heap. While I get that some in the organic farming community will write about “charging it”, it appears the industry is basically just talking about charcoal that is used as a soil amendment and to sequester carbon… This is clear on the website of the “International Biochar Initiative”.

What is biochar?

Biochar is a solid material obtained from the carbonization thermochemical conversion of biomass in an oxygen-limited environments . In more technical terms, biochar is produced by thermal decomposition of organic material (biomass such as wood, manure or leaves) under limited supply of oxygen (O2), and at relatively low temperatures (<700°C). This process mirrors the production of charcoal, which is perhaps the most ancient industrial technology developed by humankind. Biochar can be distinguished from charcoal—used mainly as a fuel—in that a primary application is use as a soil amendment with the intention to improve soil functions and to reduce emissions from biomass that would otherwise naturally degrade to greenhouse gases.

Thanks Dave for your informative and helpful post.

I was aware that ash has a high pH and is used in making soap, but I had not connected the dots that it could be detrimental to microbial life in the barrel. We only add about 1/2 a gallon per barrel. And often don’t add it because we don’t have it. Therefore, it might not be detrimental, however being water-soluble, it could be wasted effort however, it would save the effort of spreading it separately. I need to think about that.

Regarding the “bio” in biochar, you are correct that I thought the bio comes from the charging of the char with microbial life. I’ve read that in various places. It could be, that is one more area where there are a variety of opinions and points of view. As I say to students, “Organic farming is sort of like religion in there are various different opinions and each one thinks they are correct.” Thanks so much for sharing the IBI link. Will look at it shortly.

This list of material from the International Biochar Initiative may be helpful in discussions about biochar.

ECHO has a collection on Biochar that covers a broad range of investigations

Comments from network members providing information on their experiences are invaluable. Keep them coming!

Dave, IBI actually recommends adding biochar to compost as a way to make biochar a more valuable soil additive.

“Biochar straight out of the pyrolysis unit might take some time to reach its full potential in soil, because it needs its surfaces to “open up”, or “weather”. This happens naturally in soil, but the process can be sped up by mixing biochar with compost, for example. Nutrient retention with biochar is thought to improve with time, along with crop benefits. Mixing biochar with compost is a great idea, since apart from the ash (and there might only be small amounts of it in biochar), biochar is not a fertilizer in itself so the compost can provide nutrients which the biochar can help retain.”

I’ve been reading up on biochar, however have not used it yet.

What I have been seeing is recommendations for an application rate of 1-10%.

It is often recommended for the biochar to be “activated/charged” (mixed with something like compost, manure, worm castings, “tea”) prior to applying, and applied wet, because if it is applied by itself it will actually draw nutrients & moisture out of the soil and potentially have a negative impact on crops in the first year (while improving on subsequent years).

Studies on biochar have had mixed results, because some studies applied it without first charging it.

Additionally, qualities of biochar can vary (seed material burned, temperature of roasting), and soil type and conditions it is trying to resolve.

It is considered a “soil conditioner” rather than a fertiliser, it doesn’t break down in the soil like compost/manure, so provides permanent structure that many soils need, and it’s capacity to retain water, nutrients, and microorganisms means it soaks up excess that are then available to plants when needed. Compost/manure is great at providing nutrients however they break down quickly and any excess can be lost/washed away if there isn’t something like biochar or zeolite to soak it up (meaning there is more retained in the soil for dry times or less need for as much compost/manure in future).

I haven’t seen references to applying less than 1%, and unfortunately the link within the article you shared has a broken link.

Note: I have seen some reports that the higher level of biochar (10%) has a negative impact on worms, so I suspect the optimum would be 1-3%.

Thank you Luci for your post. Very interesting.
I wonder where those suggesting 1% to 10% can get that amount of biochar. I have never lived anywhere…in USA nor in other countries where that amount of biochar is available because that would be 10 tons per acre for 1% and 100 tons at 10%. Seems to me that can only be realistic in small gardens…not farms. Here in Honduras, we can buy dump truck loads of ash but not char. 10 to 100 tons of char would be valued at more than the land price.

We are preparing to begin making char using sawdust because the only place we can buy char is from those who make and sell charcoal…expensive. After sawdust, we will try coconut shells. Our first attempts were not successful because the aluminum vessel we were using melted. So, now we are preparing a steel vessel. My guess is, at best, we will be able to make 10 lbs a day. So, unless like many other additives used in organic farming where an exceedingly small about can make a big difference, we are wasting our time. But, many in KNF are using 0.0001% of their additives and enjoying success. I am hoping it could be the same with biochar.

We average making one 55 gal barrel of bokashi each day. We hope to begin adding one gallon of char to each barrel…thus a very small percentage. But, I think it is a worthwhile experiment.

Eager to hear if anyone has had success using modest amount of biochar.