BioChar Characteristics

Since 2007, when this page was first sketched into place, we've made dramatic improvements in our understanding of what terra preta is, what biochar is, and what it's function is in the soil. Some of the better references and resources are given below.

Biochar Testing Labs

Online Resourced Dedicated to Characterizing Biochars

UC Davis Online Biochar Database

Soil and Materials Science Centers

For the latest articles from Scientific Journals go to Science Direct and search for Biochar Characteristics.

The International Biochar Initiative has a great FAQ and set of characteristics information about Biochar.

Characteristics and Function of Charcoal
From: Makoto Ogawa, Effects of Soil Microbial Fertility by Charcoal in Soil

  1. Porous substance with high water and air holding capacity; Suitable habitat for some microbes and plant growth, good material for soil amendment, absorption of chemicals and humidity control
  2. Alkaline; Neutralization of acidic soil and improvement of chemical components of soil and selection of microorganisms
  3. Non organic matter ; Exclusion of saprophytes and propagation of autotrophic and symbiotic microorganisms, free living nitrogen fixing bacteria, root nodule bacteria, Frankia and some mycorrhizal fungi
  4. Low mineral content ;


As I understand it, adding fresh charcoal to the soil would have an initial effect of removing nutrients from the soil. After the sites are fillded up, the typical 'Terra Preta' effect would add on.
Adding nutrients to the char previous to the addition to soil would reduce/reverse this initial effect.
For example, adding urine.
Does anybody have any idea of the specific adsorption capacity for charcoal on nutrients?

Folke G

Folke G

I have run several experiments to see how much nurtients hardwood and softwood charcoal can absorb.
I have been able to store upto 10% w/w of a water soluble fertilizer solution on dry weight of charcoal.

At this level it could burn the root hairs on young plants if it were to be immediately released.
Fortunately the charcoal slowly releases these nutrients on an as needed basis to the plants.

Urine is rich in Nitrogen ( Ammonia, Urea ) and Phosphorus and binds well with charcoal. In some places charcoal urinals are used to reduce pollution and odor. The contents are then added to the compost heap.


I am still learning a ton of stuff about biochar. But I do know that yes, you are right about raw or fresh biochar extracting the elements out of the surrounding soil initially. This takes a while to turn around, say 2 to 3 years. Each feedstock, however, and correct me if I am wrong, has a different chemical make up, even though the final product of pyrolysis is mostly carbon. Ergo it will have a different level of requirement in attracting elements. I am currently involved with an experiment using biochar that was treated (soaked) in Worm Biol, and biochar that was untreated. It has been in the soil one year, and in three weeks I will be taking soil samples for analysis. I will take samples again in one year's time. My hypothesis is that I will find the nutrients (elements) in the soil with treated biochar showing higher rates of availability than with the soil with untreated biochar. But I need to know if it is the Biol influencing this availability or if it is that the biochar was "satisfied" and that a change in nutrient availability is actually the result of the biochar additions.
Your comment was posted in 2007, so I am sure that there is a whole lot of information on this very subject that you can find.


Rip Winkel

I live in the South of France near Toulouse. Around 4 years ago I stocked around 36 cubic metres of Plane Tree wood-chips about 2 to 3 finger size in the ruins of a building which had less than 2 centimetres of charcoal and a small quantity of broken tiles on the ground (bare earth) remaining from a fire that gutted the building around 10 years earlier. The wood-chips had been exposed to rainfall for around 2 years since the polythene covering had started to degrade with the sunlight. I noticed at that time that it was infested with wood-eating beetles, dark red in colour, around 5 centimetres long with a rhinoceros horn structure on the front of the head. I found a large number of them together with their larvae, around 3 centimetres long and about 1 centimetre thick. I ignored this for a couple of years but last October I decided to clear the area which had a generous growth of nettles and blackberries. I discovered that the wood-chips had been transformed into around 6 cubic metres of black compost, such as is sold around here as 'terreau', of a very high quality. I noticed particles of charcoal on the surface and throughout the mass and occasional beetle carcasses.

My experience with wood-chips suggests that this degree of decomposition is unusual without adding manure, urine, soil and other 'lighter' organic matter; and without turning the mass. I suspect that, with the help of the beetles to distribute the charcoal, the charcoal acted as a compost accelerator.

I find no reference to such an effect but my understanding of Biochar gives me the idea that this could be the case. I intend to repeat the experience with and without the application of more conventional compost accelerators. I will keep you informed.

Does anyone else report such an effect?

I have been using "campfire charcoal" in my wood chip pile, compost pile and the cow manure pile.
In all cases composting was grealty improved and speeded up. What was notable that the earthworms in the manure pile only lived in a narrow 10 to 15 cm band. However when ~5% screened ( < 1cm ) charcoal was mixed in,...the whole pile ~1/2 meter thick was infested with worms throughout. This happened within 4 weeks.

WOO's worms has been usiing 25% charcoal in vermicomposting with very good results. Just check th pH of the charcoal.
Earthworms don't like alkaline environments.

I noticed that in the Amazonian terra preta there was reportedly large ammounts of pottery shards as well as charcoal. The intact pottery in the region was very advanced. I think the car came from these kilns AND I THINK THE POTTERY SHARDS ACTED IN A WAY SIMILAR TO THE BIOCHAR! A POROUS PLACE FOR MICROORGANISMS, WATER HOLDING, but maybe no sequestering of gasses or maybe so.

I read in the gardening with biochar section that using wood from bamboo, pine needles or Acacia will give biochar with negligible liming capacity. Is there a list of organic materials that will give biochar with little liming capacity? Are there ways to threat biochar to avoid this effect?