Which is better - large chunks of biochar? Or lots of little pieces?

I'm sure the answer is in the book - or any one of the books available - but since I'm new to the conversation AND there's a chance to win a book, I figured I'd start here and offer an opportunity for folks to flex their knowledge.

And, I wanted to make an haiku:

Carbon farming love
Burnt offerings make gardens sing
For thousands of years

The first question I have to ask is, "what do you want to achieve?"

There is a broader point that the problem is that the field is a mess, scientifically speaking. Few studies have been conducted, and of those few around half found little or negative effect on soil carbon (it's thought the addition of so much carbon stimulates the microbes that turn it straight back into CO2). In some cases where it did show an increase in soil carbon it was compared with adding nothing to the soil (as opposed to using other common amendments such as mulching or green manuring), and nothing is known about how it holds up long term.

When you throw in the likelihood of publication bias it looks like the claims made about biochar may be grossly overblown. There are some studies out there that do show very positive results, but there are all kinds of issues with selective promotion of those studies, among other issues.

So, the short answer to your question is that even if a proper study has been conducted that might give a clue to the answer to your question, the results may not be generalisable to your land and environmental conditions, may be ambiguous in terms of carbon storage even if there were short term improvements in yields, and there may be a contrary study that was never published. So, if someone does come along with a study comparing big chunks of biochar to using lots of little pieces, that still a) may not apply to you and b) you don't know if there is a contrary study that isn't being mentioned (unless you can trust the poster to have done a thorough literature review, which I have not, although others have) or was never published. Even if you tell me what you what you want to achieve, the answer is still "it depends on a lot of factors, and the answer may not be known".

Then there are the environmental impacts of widespread use of biochar, and you can read George Monbiot on that here: http://www.theguardian.com/environment/2009/mar/24/george-monbiot-climate-change-biochar

There are responses to this, which are worth a read. Whatever the results (and the science remains, as I say, ambiguous), the commercial production of biochar is not a good idea, and that seems most likely to be the source of larger chunks of biochar. So, if you have suitable agricultural waste, by all means turn it into biochar and get someone with suitable training to come and design a trial to compare the results using your biochar with doing other things on contiguous land in your conditions on your land, and be sure to publish the results, even if they were not what you hoped for, because that tells us something about the use of biochar and pointers for further research. Buying commercial biochar produced as a result of planting trees is not as environmentally friendly as you may have been led to believe, so please don't do that, and do something else instead.

As Neil indicated, the story is not a done deal when it comes to biochar. I follow some biochar discussion groups, and the researchers and field people on them all agree that biochar is not one simple product, nor is it beneficial across the board. Research is still in its infancy stage. As since there are businesses and people's egos involved, there is no shortage of attempts to discredit or attack what is perceived to be the competition. It makes it difficult for farmers to get accurate information.

Some of the significant variables...
...what material is being used to make the biochar
...what temperature is used in the "burn"
...what sort of stove or retort system is being used to create the char
...whether it not the char is quenched, and if so, with what
...how it is applied or incorporated
...what the soil type is that the char is being applied to
...what the climate situation is on the farm
...(And your question), what is the size of the particles.

There seem to be no definitive answers yet.

That being said, I make some biochar from tree trimmings for use on my own farm. I've dug chunky char into wet ground and it seems to help with drainage. I've added it in a more finely chopped up size (I use a stick blender in a five gallon bucket of urine/compost tea) to my compost or directly to the garden beds. I truely can't tell if it makes a difference because I use an assortment of soil amendments at the same time. But the biochar treated areas look and feel nicer than the non treated areas. And I don't see any detrimental issues from its use.

Let me show off my mental simplicity 😉. We burn a variety of native wood in our stove - oak, pecan, elm and box elder. Nothing processed or treated. The resulting charcoal is as close to bio char as we're going to get. What are the advantages and any disadvantages to spreading this plain old charcoal (just charcoal, not ashes) on our gardens?

Judy Bowman wrote:Let me show off my mental simplicity 😉. We burn a variety of native wood in our stove - oak, pecan, elm and box elder. Nothing processed or treated. The resulting charcoal is as close to bio char as we're going to get. What are the advantages and any disadvantages to spreading this plain old charcoal (just charcoal, not ashes) on our gardens?

In small quantities it's unlikely to do any harm and may well do some good. I'd suggest mixing it with compost when you use that as soil remediation. The damage seems to have been caused when adding large concentrations of biochar in some circumstances. That's unlikely to apply to the kinds of quantities coming out of your stove (although you might want to look at efficiency if you are producing charcoal, not ash).

Taking a note from Mother Nature, I don't see any problem with adding your charcoal to the soil. Mother Nature does it all the time with forest fires. In fact, forest fires use to be far more common, so charcoal was a natural component to the forest soil.

My projects are many and my time is short, but one of the things I would like to do this year is make a fairly large amount of biochar and add it to the bedding in my chicken coop all winter. I'm hoping it will absorb odors and when I compost the bedding in the spring, it will be added to my gardens.

Judy Bowman wrote:

Neil Layton wrote:

In small quantities it's unlikely to do any harm and may well do some good. I'd suggest mixing it with compost when you use that as soil remediation. The damage seems to have been caused when adding large concentrations of biochar in some circumstances. That's unlikely to apply to the kinds of quantities coming out of your stove (although you might want to look at efficiency if you are producing charcoal, not ash).

Thanks. We do have less than 100% efficiency with our wood cook stove, but we don't mind producing a little charcoal along with the ash. We save it to use for grilling in the summer, etc. so it's actually part of our overall system of things.