Biochar: What Is It and How Does It Help My Soil?

Biochar 101

Biochar, the GREEN Charcoal - the new face on plain black charcoal. As one researcher concluded “biochar [as we understand it] is at the end of the beginning and has the potential to play a dynamic role in the future of humanity and its societies. The “beginning” revolves mostly around the discovery and initial investigation of the charcoal rich “Terra Preta” soils of the Amazonian rainforests of South America. The realization that these biochar-rich soils 1) maintain balanced moisture levels during wide climate changes, 2) improve air permeability in otherwise dense clays soils, 3) elevate cation exchange capacity in otherwise sluggish soils, 4) increase buffering of soluble organic carbon, 5) and all the while facilitating synergistic interactions with soil microbes, seems all to good to be true. But, there is more. 6) Like activated carbons some biochars have activity levels high enough to act as detoxifiers of poisoned, sterile or dying soils.

As for its impact on the environment, it could actually be global. Biochar may even be part of the solution to man’s destructive impact on the thin veneer we call our atmosphere. Biochar may be able to somehow detoxify our earth ship’s air supply of excessive CO2 just as activated charcoal adsorbs CO2 in nuclear submarines and space stations. So what is biochar? Biochar is the relatively new word for charcoal derived from renewable carbon-based resources (biomass) such as wood, nut shells, corn stover, and switch grass, as opposed to non renewable fossil-based carbons such as coal and oil, rubber tires and plastics. Biochar is also that charcoal destined to be used primarily for soil enrichment. More technically, biochar is “thermally-modified biomass.” Biomas is living matter, or dead or decomposing matter that was once living. Biochar is what is left over when the volatile material in biomass is cooked off, and the remaining carbon has been structurally changed, such that it does not biologically decay as all forms of biomass eventually do. This unique characteristic allows biochar to remain stable in the soil for long periods of time. This modification process combines pyrolysis and carbonization. Pyrolysis is a chemical breakdown of organic material into gasses that boil off. Carbonization is the chemical buildup of carbon atoms into solid structures which remain. Burning Matchstick You might better understand this process by burning a wooden match. As the flame moves down the matchstick charcoal is left behind. These remaining carbon structures are extremely random yet equally stable chemically. Consequently this biochar is quite indigestible even for microbes. So…? Biochar, as a soil amendment is very stable. Unlike other raw material like fertilizers, additives, composts, or manures, biochar is not assimilated, transformed, or broken down, but remains in the soil through successive generations of biomass. This dry land reef, if you will, acts as both a water and nutrient reservoir during times of extended draught. Does biochar actually benefit soils and increase crop production? YES! Can biochar rich soils decrease the dependency on commercial fertilizers? YES! Can biochars sequester CO2? YES! Can biochars help to retain essential soil nutrients from being leached out by rain or irrigation? YES! So, where can I get some? As we leave “the beginning”, the interest in biochar, helped along by such diverse interests as economics, climate control, giant pumpkin growers, organic gardeners, development workers, researchers… has created its first hurdle - finding some biochar to experiment with. Having found a source how does one know if it is a “good” biochar or not? Sources Currently, of all the potential sources, there are only three that are realistically accessible to the individual, experimental farmer, or research school interested in using biochar. One is purchasing conventional lump charcoal; the second is small-scale use of simple drum retorts; and the third is making your own char residuals from Top-Lit UpDraft (TLUD) gasifying stoves.

Biochar from Lump Charcoal In a chapter entitled “Lump Charcoal from Commercial Sources” (H McLaughlin PhD, Paul S. Anderson PHD, Frank E. Sheilds, Thomas B. Reed PHD, All Biochars are Not Created Equal, and How to Tell Them Apart, August 2009) the author briefly explained the nature of charcoal briquettes. “Conventional lump charcoal was a widespread product prior to WWII, but has been replaced by charcoal briquettes after the war. Currently, most charcoal briquettes are a mixture of powdered devolatilized coal, a small portion of raw or carbonized sawdust, and intentional ash additives - intended to create the “complete charcoal cooking experience.” All that lovely white ash, indicating the coals are ready for cooking, is limestone, straight from the mine. Nowadays, lump charcoal is a boutique cooking fuel, which is gaining popularity and distributed almost anywhere outdoor cooking supplies are sold, including most hardware stores. It is generally made from clean wood scraps, such as residues from furniture making, and appears as solid lumps that still exhibit the grain of the original wood. While it is not inexpensive, lump charcoal is certainly affordable in the smaller quantities that a home garden might require to achieve recommended biochar levels in the soils of 3 to 10 weight percent of the soil mass in the root zone.

However, an underlying issue remains: Is lump charcoal a good candidate for use as a biochar?” The author gathered a number of samples of popular retail lump charcoal and analyzed their respective activity levels – that is, how much adsorption capacity did each lump charcoal have. Two things were clear from the study. 1) not all charcoals/biochars are created equal. 2) the process of carbonization has a direct bearing on the respective activity levels. One of the selling features for cooking lump charcoals is the ability to light easily. To achieve this some producers cook the wood quickly at low temperatures (below 450°C) which leaves behind higher levels of low molecular weight combustibles which help the lump charcoal ignite more easily. But… These low molecular weight components compose most of what has been termed as “mobile matter”. According to the author this soluble mobile matter has two important features when reviewing biochars. “First, there is evidence that mobile matter leaches into the soil and provides a soluble carbon source, which can cause a short-term nutrient deficiency for the plants by stimulating soil microbe growth that competes with the plants for available nitrogen.” This initial draw down on certain soil nutrients can be crucial for some plants and could determine whether a crop will mature in time for harvest or not.  The mobile matter level in lump cooking charcoal is a concern because the charcoal is expected to light without the addition of liquid charcoal starter.

Consequently the carbonization process may be regulated so as to achieve more of these low molecular weight volatiles (mobile matter), which may be counterproductive when thinking of an ideal biochar. Second, the elevated amounts of mobile matter are likely to disappear within a single growing season and not contribute to the long-term properties of the soil. As such, the mobile matter portion in biochar is bought and paid for, but represents less long-term value as a soil amendment. Water and ash provide similarly reduced long-term value in the biochar, but most people recognize that situation and purchase accordingly. NOTE: As a work around to this potential draw down on soil nutrients CHARCOAL GREEN® BIOCHAR PLUS begins as a pure biochar then is inoculated with beneficial soil microorganisms and enriched substratesYou can see the RESULTS for your self. In addition to the Mobile Matter assay, Adsorption Capacity was tested because that is a crucial property of biochar that is created at the time of manufacture and is unlikely to improve over time. 15 randomly selected commercial lump charcoals were tested. In general, the best of the lump charcoals had adsorption capacities comparable with other wood biocarbons (not manufactured for the lump charcoal market). Unfortunately, the average lump charcoal mobile matter was over twice the average level of 10% for the biocarbons. Furthermore, it was apparent from extremely random percentages among the 15 samples that one cannot assume the mobile matter or adsorption capacities based on the relative bulk density of the end product. Eighteen samples of different lump charcoals produced by the same manufacturer were also tested for adsorption capacities to see how much lump charcoals might vary when produced under the same cooking process. The results showed that when different woods are cooked under the same process it results in a much more uniform range of adsorption capacity and relative density. Considering there was as much as a 700% (seven-fold) difference in adsorption capacities among the various samples of commercial lump charcoal, the authors stressed, these three main conclusions:

  1. Currently available biochars vary significantly in key properties
  2. Great attention should be taken to know the characteristics of any charcoals being added to soils, and
  3. Reports of the responses (whether favorable or unfavorable) of plants and soils to biochar applications are of questionable value without corresponding knowledge of the characteristics of the applied biochars.

NOTE: CHARCOAL GREEN® PURE BIOCHAR is produced from one of the above commercial lump charcoal that scored HIGHEST in activity levels! Charcoals from Small Retorts Many variations of small charcoal-making retorts appropriate for personal experimentation are discussed on the Internet, including: Charcoal from Gasifiers Again, there are a number of designs. While some larger prototypes have been developed most seem to produce minimal amounts of charcoal. But as the interest in biochar grows no doubt larger units will become more common. For the curious or the innovative these links may be a starting point. The “good feel” test Lastly is the hands on test. Properly carbonized wood forms a rigid, easily crushed material that lacks pockets of under- carbonized material. This material differs from the partially burned logs that linger after the campfire goes out. In addition, fully carbonized chars are also not particularly “greasy” to the touch. They are dirty and make copious amounts of black dust, but that dust will wash off one’s hands with just water. If it takes significant amounts of soap to remove the char powder from the pores of the skin, then the char has significant amounts of mobile matter, with the associated concerns discussed previously. Ignited, Quenched, Perished, Endowed Biochar, a new remedy for undernourished, depleted, sick, sterile or dead soils. Perhaps a remedy for the air we all breathe. Clearly the potential to be an economic catalyst for countless subsistence farming communities. As the famous Roman scientist Pliny said long ago of charcoal, so might it be said again of biochar today. “It is only when ignited and quenched that charcoal itself acquires its characteristic powers, and only when it seems to have perished that it becomes endowed with greater virtue.”

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