Biochar is a highly porous, carbon-rich substance produced by heating organic matter in a low-oxygen environment – a process called pyrolysis. Biochar is known to improve soil quality and for this reason is frequently used in farming and gardening.
When added to soil, biochar can enhance its quality by retaining moisture, increasing nutrient retention, and promoting healthy microbial activity.
Biochar is believed to have been used in soil management for thousands of years in order to improve land fertility and crop yields. Anthropologists speculate that indigenous peoples in the Amazon basin created regions of fertile soil called “Terra Preta‘” (dark earth) by using biochar produced through ‘slash and char’ methods.
Biochar’s Physical Properties
The porous structure of biochar provides a large surface area for microbial habitats and water retention, improving soil health and aiding in carbon sequestration.
Biochar’s porosity and large surface area allow it to efficiently adsorb nutrients and water. This provides hydration and nutrient availability to plants and prevents nutrient runoff.
Soil aggregation is enhanced by biochar because it creates a microbial environment that generates organic compounds that bind soil particles together. Its porous structure prevents compaction and provides an aerated framework for improved soil structure and stability.
Biochar’s Chemical Interactions With Soil
Biochar can be used to maintain an optimal pH range for plant growth. When used as a soil amendment in acidic soils, it can help to stabilize the pH and prevent rapid fluctuations.
Biochar can help to neutralize alkaline soils with high pH levels by absorbing excess alkalinity. It can also immobilize or detoxify soil contaminants by trapping heavy metals and pollutants, preventing their mobility and reducing their bioavailability to plants and the environment.
How Biochar Benefits Microorganisms In Soil
The porous structure of biochar serves as an ideal habitat for diverse microbial communities. It creates an environment conducive to mycorrhizal fungi and nitrogen-fixing bacteria growth, which enhances plant immunity and nutrient uptake.
Biochar can deter certain soil pathogens by altering the soil environment. Some pathogens thrive in specific pH conditions, and biochar can modify the soil pH to make it less hospitable for certain pathogens. The presence of microorganisms outcompetes and suppresses the growth of harmful pathogens.
Pyrolysis is a process in which carbon-based matter is heated in an oxygen-deprived environment at very high temperatures (400-800 degrees Celsius or 750-1470 degrees Fahrenheit), causing it to thermally decompose into a charred substance. Limiting the amount of oxygen in the heating environment prevents combustion and allows the material to decompose into volatile gasses and porous solid residue (charcoal or biochar) through heating.
The characteristics of biochar depend on three factors used for its production: temperature, duration, and the feedstock.
- Higher temperatures during pyrolysis result in increased carbon content and surface area, and a greater release of volatile matter, which creates a more stable carbon structure.
- The duration of pyrolysis, known as residence time, affects the amount of decomposition. Longer residence time increases the breakdown of the feedstock, yielding higher carbon content and biochar stability, but excessively long residence times could lead to ash content or decreased biochar yield.
- The type of biomass used as feedstock to produce biochar significantly affects its properties. The feedstock’s lignin, cellulose, and hemicellulose content, in addition to its mineral composition, influence the pH, surface area, porosity, and nutrient retention of the biochar produced.
Pyrolysis alters the molecular structure of biomass by decomposing the material into simpler forms: char, oil, and gasses. After undergoing pyrolysis, the material is less volatile and is more structurally stable than the original feedstock.
Pyrolysis also changes the chemical composition in organic materials by eliminating the presence of reactive oxygen-containing compounds, resulting in a higher ratio of carbon to oxygen and a more chemically stable material.
Biochar Compared to Charcoal
Biochar, charcoal, and activated carbon are all carbon-rich solids produced through pyrolysis, but they are used for different applications.
The main difference between biochar, charcoal, and activated carbon is that biochar is intended for agricultural purposes, charcoal is intended for cooking and heating, and activated carbon is intended for water and air filtration and purification.
Biochar is more porous and has a larger surface area than charcoal, which allows it to improve the structure of soil, increase airflow, and house healthy microbes. Unlike biochar, charcoal may contain ash and chemicals that are harmful for plants. You can tell if the volatile gases from biochar production were allowed to condense onto the char because of the smell that remains. If your biochar has a ‘camp fire’ odor you may want to reconsider using it for soil health.
Biochar captures carbon from its biomass source material and keeps it from being released into the atmosphere, thus cutting down on greenhouse gas emissions. Charcoal decomposes much more quickly than biochar and releases its carbon into the atmosphere where it can contribute to global warming.
Environmental Implications: Carbon Sequestration and Beyond
Biochar acts as a stable form of carbon, which can be sequestered in the soil for potentially hundreds to thousands of years, contributing to long-term carbon storage and reduced atmospheric carbon dioxide levels.
Biochar provides an alternative to the traditional burning of bio-waste, mitigating greenhouse gas emissions like nitrous oxide and methane.
Besides offering direct benefits to soil and plant health, biochar has broader environmental benefits, such as providing a use for organic material that would be discarded and saving land that would be deforested for waste disposal.
Further Applications Derived from Science
Biochar has also been used to remediate polluted soils by trapping heavy metals and pollutants, which reduces their availability and mitigates their impact on the environment. Because biochar improves soil structure, nutrient retention, and water-holding capacity, it is often used for enhanced plant growth in agriculture, contributing to improved crop yields in cereal and grain, such as corn, and vegetables like tomatoes and peppers.
Beyond soil improvement, biochar has innovative applications in water filtration, where its porous structure is used to capture and filter pollutants out of water, including metals.
Biochar has also been explored as a supplement in animal feed for improved growth performance, animal welfare, and reduced methane emissions. In livestock farming, improved blood profiles, egg production, and ability to resist gut pathogenic bacteria have been attributed to the addition of biochar in animal feed.
Learn more about biochar and discover all of its benefits for yourself!