Biochar crystal lattice

What are the benefits of biochar for the soil?

Many of biochar’s benefits stem from its unusual porous structure, which provides an incredibly large surface area for the material. A well-made biochar can have a surface area of ​​over 185 square meters per gram. In comparison, the portion of the tennis court used for singles matches is 195 square meters.


Biochar is composed of a porous, carbon-rich base that enhances soil vitality by:

 – Improved infiltration and water retention;

– Prevention of leaching of nutrients from the soil;

– Diversification and increase in the number of beneficial soil microorganisms

– Reducing the acidity of the soil – for example, by removing unwanted aluminum ions, thus raising the pH of very acidic soil.

– Retention of fertilizers in the soil and adsorption of beneficial ammonium ions.

As a rule, most agricultural enterprises do not naturally destroy a large amount of natural waste generated from the fall of leaves and fruits, as well as from wood waste that is formed as a result of logging. And at the same time, modern agriculture based on chemistry significantly reduces the carbon content of the soil. Nitrogen fertilizers in combination with soil cultivation accelerate microbial respiration, burn carbon in the soil faster than it is replaced. Due to the loss of their original soil organic carbon and fertilizers derived from organic materials, soils are almost constantly fed on mineral nutrients and pesticides to maintain their previous yield levels.

Is it possible biochar could replace some of this missing soil carbon? Nature produces megatons of biochar through natural forest fires in forests. Prairie fires can also generate a lot of biochar. There is a practice of planned fires of separate forest belts, in order to obtain charcoal in a natural way and increase the resistance of trees to natural fires.

Overall, biochar can act as a phenomenal agricultural catalyst, working synergistically with microorganisms and other soil components to improve soil fertility in the long term. The researchers reported a 30–300% increase in yields.

Biochar is made by heating biomass without oxygen. This process is called pyrolysis, which involves drying the biomass and then releasing flammable vapors.

So what explains the effectiveness of biochar? Let’s examine the pore structure of biochar under an electron microscope.

The resulting coal resembles a blackened, compressed version of the original biomass. But now there is very little oxygen in it. Microscopically, it inherits most of the structure of the original biomass. The only difference is that it has been converted from lignin, cellulose and hemicellulose to one of the carbon allotropes. What you will find is a collection of scattered graphite crystals based on hexagonal carbon rings with some remaining hydrogen and oxygen, as well as minerals (ash) that were in the feedstock. They are very resilient and take a long time for microbes to break down, which explains the biochar’s long lifespan.

Fused carbon rings form a special bond with each other that allows electrons to travel internally in the molecule, creating electrical properties similar to those found in engineered carbon materials such as graphene sheets and metal nanotubes. Depending on the pyrolysis temperature and the final state of the elements, biochar can be an insulator, a semiconductor, or a conductor of electricity. The electrically active condensed carbon rings are an excellent base for redox reactions, which are important for soil biochemistry, acting as a catalyst. As soils, microorganisms use aromatic substances as an electron donor. Biochar helps bacteria exchange electrons with each other, improving their effectiveness as a microbial community.

Due to its pores and electrical properties, biochar is capable of both absorption and adsorption. Absorption is a function of the pores. Large pores absorb water, air and soluble nutrients just like a sponge. Adsorption is dependent on surface area and charge. The surface of biochar adsorption materials is used as an electric sponge by means of electrochemical bonding.

Porosity is manifested on many scales, from large vessels and cellular structures preserved from the original biomass to nanopores formed by tiny molecular dislocations. The amount of porosity depends mainly on the starting material, particle size and the highest pyrolysis temperature. Temperature determines how much volatile components (hydrogen and oxygenates) will be removed and how much pure carbon graphite is formed. Typically, the porosity increases as more volatiles are removed. In addition, at temperatures approaching 1000 degrees Celsius, the pores begin to break down or melt. For this reason, the highest pyrolysis temperature point is a key variable to be aware of when producing biochar for a specific purpose. The porosity will also depend on the feedstock, as feedstocks with a high ash content, such as grass, react to heat in a completely different way than feedstock with a low ash content, such as wood or bamboo. For wood raw materials, porosity usually peaks at around 750 degrees C.

And that’s not all! At temperatures of 400-500 degrees, wood resins do not burn, but harden and cover the pores of charcoal with a thin layer. The cured resins are highly ion exchangeable, i.e. an ion of any substance easily attaches and then is firmly held, and is not washed out even by rains. But, the substance so firmly held by the surface of the coal is easily absorbed by the roots of plants or hyphae of mycorrhizal fungi. Surely you are familiar with the term “symbiosis”? So: bacteria living in the soil and on the roots of plants secrete enzymes that can dissolve minerals. The resulting ions are captured and retained by the biochar resin, and plants, as needed, “remove” these ions from the coal with their roots and feed.

A considerable amount of nutrients enters the soil with rain or water for irrigation. Most of the elements are also captured and retained by the charcoal. As a result, it turns out that the soil, with the biochar introduced into it, is able to feed the plants by itself, without fertilizers.

From the above, we deduce, for convenience, the unique properties of biochar:

  • An excellent storehouse of macro and microelements, nutrients;
  • Increases the porosity of the earth thousands of times;
  • Accelerates plant growth;
  • Increases the availability of Ca, Mg, P and K in soil;
  • Maintains soil moisture;
  • Stabilizes the soil;
  • Increases the fertility of the land;
  • Prevents the earth from sticking into lumps;
  • Serves as a transport route for mycorrhiza and bacteria, accelerates the intake of nutrients by the roots;
  • Increases total biomass;
  • Stimulates the fixation of symbiotic nitrogen in the root system.


How long can biochar last?

Biochar is capable of providing long term soil vitality and lasting hundreds to thousands of years. For example, dating of radioactive carbon carried out on terra preta soil in the Amazon region, which is still in use today, showed that carbon was formed from 500 to 7000 years ago (identified as before 1950 AD).

Biochar’s extraordinary longevity stems from the fact that it contains aromatic carbon compounds that are tightly bonded to each other and impart exceptional chemical stability.