Biochar is a fancy name for charcoal, coined because of the specific use of charcoal as a soil amendment rather than as a fuel. Like charcoal, biochar is the solid material left behind when organic material is burnt in low levels of oxygen. This can happen naturally such as when belowground peat deposits burn but more commonly is engineered by humans in special combustion chambers through a process called pyrolysis.
What happens in pyrolysis is that rather than combust completely to ash, as when we burn wood on an open fire, there is not enough oxygen for all the organic material to burn. Instead the organic material forms a resistant black substance that is almost complete carbon, the char, and liquid gas products.
When biomass smolders for a long time at low temperatures it generates mostly char and when the temperature of pyrolysis is higher and the process faster more gas is produced.
The actual structure of the char is like a honeycomb with air pockets between a fine matrix of carbon atoms.
What are the Benefits of Biochar?
When a plant grows it uses water and nutrients from the soil. Fine roots grow into the tiny spaces between the soil particles and nutrients flow across from the soil water into the cells in the roots. It is a world we cannot see that is dependent on microbial activity in those small soil spaces.
Biochar is carbon with a microscopic honeycomb structure with the actual size of the pore spaces dependent on the type of biomass used and the method of pyrolysis. This honeycomb structure is ideal for both holding water, providing micro-habitat for microbial activity and enhancing nutrient exchange between the soil and plant roots.
The carbon in char is stable and resists further degradation or decomposition even when it has been in the soil for hundreds of years – read article on best soil amendments for vegetable garden.
These properties make biochar an excellent soil amendment that can help improve poor or degraded soils.
What we call poor soil is soil that has low levels of plant nutrients, or has nutrients locked away in clouds that roots cannot penetrate, has low oxygen levels and is either dry or waterlogged.
All these conditions are hard for plants to prosper and this, in turn, limits soil biological activity as there are fewer organic inputs to sustain soil animals and microorganisms.
Healthy soil that supports plant production is:
has a stable physical structure
high in carbon and
These properties promote efficient nutrient exchange and strong plant growth.
Applying soil amendments can help improve soil health and biochar is one of the better amendments to apply because it:
helps retain water
improve soil water quality
reduces nutrient losses (leaching)
helps lower acidity
Together these benefits can also reduce the need for fertilizers and irrigation. The good thing is that these benefits can apply to the soil in your garden as well as an arable field.
The biochar opportunity
These options are now far more difficult as most of the usable arable land is already in use, fertilizer use is becoming less effective [and more costly], and genomics has already made its biggest gains.
Making matters worse is that a significant amount of agricultural land is degrading after many generations of crop production. In many areas, soil quality is declining with loss of carbon and nutrients and, at the extreme, is being lost to wind or water erosion.
The biochar opportunity is to achieve agricultural production gains through a focus on soil quality by adding carbon to the soil.
Biochar is ideal for this purpose. It is an inert form of carbon that would immediately increase the carbon content of the soil. The honeycomb structure of biochar increases the surface area of soil providing vital micro-sites for microbial growth and nutrient exchange. The honeycomb also helps retain moisture that, in turn, promotes biological activity.
An important bonus is that adding carbon to the soil is a form of carbon sequestration, an activity that will help offset greenhouse gas emissions.
Biochar is one of those rare opportunities to recover biomass that would otherwise go to waste and make a material that can help solve problems in agriculture and climate change mitigation.