Differences between biochar and charcoal

I thought this was a good explanation, showing the differences between the two:
John S
PDX OR

https://www.wastex.io/post/biochar-vs-charcoal

What caught my eye was this:

"Biochar's pH can vary more widely than charcoal, typically ranging from slightly acidic (around 4.6) to moderately alkaline (around 9.3). This variation depends on the feedstock used and the production temperature. "

Creating a low pH (acidic) biochar would be extremely useful. But what feedstock? What temperatures?

I have read that what you put in matters a lot.  Coniferous wood makes a very different end product than hardwoods.  I remember them saying that it was preferable in some places to make biochar out of conifers. I think it was because the conifer soil is normally very acidic, so it can put your soil out of whack.  I guess if you have alkaline soil and you don't want it to get more that way, conifers are probably a good idea.  We have very acidic soil here.

John S
PD XOR

Yes, all the literature seems focused on "how to fix acidic soil with biochar."

My searches on "how to reduce biochar acidity / pH" basically boil down to "add elemental sulfur." Which helps me not.

I wonder how the source above came up with their information. Some more details (or links) would be very helpful for those of us trying to reduce pH in our soil.

EDIT: I mistyped above -- my goal is to increase biochar acidity / reduce pH. Apologies for being unclear.

Biochar pH is going to be a function of two main variables: Feedstock mineral content, and highest treatment temperature. Hardwoods tend to have more minerals than coniferous species, so the biochar will have more embodied ash and a correspondingly higher pH. Softwoods like pine and fir don't produce nearly as much ash and yield a more neutral or even acidic biochar.

At lower temperatures, the reactions of pyrolysis form various hydrocarbons that bond to the carbon molecules of the char substrate. These are reactive, often acidic, and tend to lower the pH of the biochar. Higher process temperatures destroy most of these substances and leave behind more pure nonreactive carbon along with the minerals, so the resulting biochar will be more alkaline.

I'm a little surprised at that cited article's claim that charcoal is higher in pH. I would expect products made at low temperatures (to retain more of the hydrocarbons for easy lighting and greater heat value) to be more acidic in the same way biochar is. Also, the realistic range for biochar production is more like 350-750 C. Below that the pores are plugged, and once you get around 800 degrees the structure turns to graphene sheets and porosity decreases due to the flattening effect.

If you're trying to fix acidic soils, go for hardwoods and high temperatures. If your soils are alkaline (or you're growing acid-loving plants) then stick to conifers and keep the temps down. Post-treatment like composting or washing with rainwater will also lower the pH of the finished product.

Excellent answer, Phil.

John S pdx or

John Suavecito wrote:
I thought this was a good explanation, showing the differences between the two:
John S
PDX OR

https://www.wastex.io/post/biochar-vs-charcoal

Hi,
In my opinion, the link provided does not offer an accurate explanation of the differences between biochar and charcoal.
They are essentially equivalent materials, except that biochar is produced at higher temperatures and therefore has completely clean internal “channels” and is functional immediately after application. In contrast, charcoal is produced at much lower temperatures, and its “channels” are not completely clean at first—they are filled to some extent with unburned residue. This residue must be broken down by bacterial activity, a process that can take months or even years.
If charcoal is used as a substitute for biochar, it must be finely ground. It can be obtained from companies that produce charcoal for barbecues, where this fine fraction is essentially “waste” for these companies’ main business during the charcoal sorting process. As for the durability of both types of charcoal, there appears to be no difference between them.

I completely disagree.  Charcoal has wood inside it. It's made for burning. BIochar is made for agriculture.  When you crush charcoal, the wood comes out. It will rot fairly quickly. Biochar stays the same for hundreds of years.  Biochar is a home base to set up healthy microbes that will help your soil.  Charcoal still has lots of tannins and other chemicals in it. BIochar is mostly just carbon, which is being sequestered.

John S
PDX OR

I have wondered if aromatic residues in char might contribute to the long term soil building qualities by preserving organic matter that would otherwise have been oxidized and metabolized?

John Suavecito wrote:I completely disagree.  Charcoal has wood inside it. It's made for burning. BIochar is made for agriculture.  When you crush charcoal, the wood comes out. It will rot fairly quickly. Biochar stays the same for hundreds of years.  Biochar is a home base to set up healthy microbes that will help your soil.  Charcoal still has lots of tannins and other chemicals in it. BIochar is mostly just carbon, which is being sequestered.

John S
PDX OR

Hi John,
Thank you for your comment!
I think we actually agree completely. It’s just a minor language barrier and terminological mix-up on my side. (By the way, as a small joke—I realized your last name "Suavecito" translates very easily into my native Czech language, but it cannot be translated literally into English very well, so we both have to deal with language barriers here!)
I actually had to consult my AI assistant (!) about this to understand where the misunderstanding was. The robot immediately explained to me that in America, when you hear the word "charcoal," you naturally think of standard commercial grilling briquettes. You are 100% right about those—they are produced at lower temperatures and are full of unburned wood cores, tars, tannins, and chemical additives.

I would NEVER put that into my soil either. It would damage the microbes and rot quickly.When I used the word "charcoal" in my posts, I was strictly referring to pure, raw lump carbon from high-temperature pyrolysis with zero chemical additives. In my native language, we use the same word for both, which caused this confusion.
I understand now that in English, this pure material must be called "biochar" once it is intended for agriculture.
I will make sure to use the correct term "biochar" from now on.

Thanks for keeping the standards high and helping me clear this up!

For me, it's such a long-term project that I don't mind if the charcoal is incompletely burned. It all gets buried in the garden anyway and mixed with all the plant matter. Maybe it takes a year or a few years to charge, I am fine with that. Last fall I dug a trench in the garden and cut through a layer of ash and charcoal from my fireplace. That layer was completely filled with roots. The plants clearly liked growing into that layer.

The original terra preta was simply cooking fire waste and burning off fields to clear them for planting. A process that took hundreds of years.

Great clarification, Pavel. Now , you have me curious about what Suavecito means in Czech.
John S
PDX OR