What Is Biochar? A Complete Beginner's Guide
Published by Sweethill Biochar
If you've recently come across the word biochar, you're not alone. Once known mainly within scientific and agricultural circles, biochar is now gaining attention from gardeners, farmers, environmentalists, and policymakers alike. It has been described as a tool for improving soil health, increasing crop resilience, storing carbon, and even helping to address climate change.
But what exactly is biochar, and why is it generating so much interest?
In this guide, we'll explore what biochar is, how it's made, where it comes from, how it works in the soil, and why researchers around the world believe it could play an important role in building more sustainable agricultural systems.
Whether you're completely new to the subject or looking to deepen your understanding, this guide provides an evidence-based introduction to one of the oldest—and most promising—soil amendments known to humanity.
What Is Biochar?
Biochar is a stable, carbon-rich material produced by heating organic matter, known as biomass, in a low-oxygen environment. This process is called pyrolysis.
Unlike burning, which rapidly converts plant material into carbon dioxide and ash, pyrolysis transforms much of the carbon within biomass into a stable form that resists decomposition.
The resulting material resembles charcoal in appearance but differs significantly in its intended purpose. While charcoal is generally produced as a fuel, biochar is designed to be incorporated into soils to improve their physical, chemical, and biological properties.
Modern biochar can be produced from sustainably sourced wood, forestry residues, hedge trimmings, agricultural by-products, and other forms of plant biomass. Regardless of the feedstock used, the goal is the same: to create a highly porous material capable of supporting healthier soils while locking carbon away for the long term.
A Brief History of Biochar
Although biochar may sound like a modern innovation, its origins stretch back thousands of years.
The most famous example comes from the Amazon Basin, where Indigenous peoples created exceptionally fertile soils known as Terra Preta, or "dark earth." These soils were enriched with charcoal, food waste, pottery fragments, bones, and organic matter over many generations.
Unlike many tropical soils, which lose nutrients quickly, Terra Preta remains remarkably fertile even today—centuries after it was first created.
Scientists studying these ancient soils discovered that the charcoal component played a crucial role in improving soil structure, supporting microbial life, and stabilising organic matter. This research inspired modern interest in biochar and helped launch decades of scientific investigation into its potential uses.
Today, researchers continue to study Terra Preta as an example of how traditional land management practices can inform modern sustainable agriculture.
How Is Biochar Made?
Biochar is created through pyrolysis, a thermal process that heats biomass in the absence—or near absence—of oxygen.
Because there is very little oxygen available, the material does not burn in the usual sense. Instead, it undergoes a series of chemical reactions that separate the biomass into three main products:
Biochar, the solid carbon-rich material.
Bio-oil, a liquid containing organic compounds.
Syngas, a combustible mixture of gases that can often be used to help power the pyrolysis system itself.
The exact characteristics of biochar depend on several factors, including:
The type of biomass used.
The moisture content of the material.
The temperature reached during pyrolysis.
The length of time the material is heated.
Lower temperatures generally produce biochar with more volatile compounds, while higher temperatures often create a more stable, highly porous structure. Researchers continue to investigate how different production methods influence biochar's performance in different soils.
Why Is Biochar So Porous?
One of biochar's most distinctive features is its extraordinary internal structure.
Viewed under a microscope, biochar contains an intricate network of tiny pores left behind by the original plant cells. These microscopic cavities create an enormous internal surface area.
Rather than simply existing as pieces of carbon, biochar particles function like miniature habitats within the soil.
These pores can:
retain water
hold dissolved nutrients
provide shelter for beneficial bacteria and fungi
improve air movement through the soil
reduce nutrient loss through leaching
This porous structure is one of the main reasons biochar can continue influencing soil properties for many years after it is applied.
How Does Biochar Improve Soil?
Unlike fertilisers, biochar contains relatively small amounts of plant nutrients. Instead, it improves the environment in which plants grow.
Scientists generally group biochar's effects into three broad categories.
Physical improvements
Biochar can improve soil structure by increasing pore space, reducing compaction, and improving aeration. In sandy soils, it may increase water retention, while in heavier clay soils it can contribute to improved drainage and root penetration.
Chemical improvements
The large surface area of biochar enables it to retain positively charged nutrient ions such as potassium, calcium, and magnesium. This property, known as cation exchange capacity (CEC), helps reduce nutrient losses and can improve nutrient availability over time.
Biological improvements
Healthy soils are home to billions of microorganisms. Many beneficial bacteria and fungi colonise the microscopic pores within biochar, where they are protected from drying, predation, and environmental fluctuations.
These microbial communities play an essential role in nutrient cycling, organic matter decomposition, and supporting healthy plant growth.
Biochar and the Carbon Cycle
Perhaps the greatest scientific interest in biochar lies in its potential contribution to climate change mitigation.
Plants remove carbon dioxide from the atmosphere through photosynthesis, storing carbon within their stems, leaves, roots, and branches. Under natural conditions, much of this carbon returns to the atmosphere when plants decompose or burn.
Pyrolysis changes this process.
Instead of allowing the carbon to cycle rapidly back into the atmosphere, pyrolysis converts much of it into highly stable carbon structures that decompose extremely slowly.
When biochar is incorporated into soil, this carbon may remain stored for centuries or even millennia, depending on environmental conditions.
This long-term storage process is known as carbon sequestration and has attracted growing attention from researchers and policymakers seeking practical methods of reducing atmospheric carbon dioxide concentrations.
Is Biochar a Fertiliser?
This is one of the most common misconceptions.
Biochar should not be considered a fertiliser.
While it may contain small quantities of minerals depending on how it was produced, its primary role is to improve the soil's ability to retain water, nutrients, and beneficial microorganisms.
For this reason, many growers combine biochar with compost, worm castings, or well-rotted manure before application. This process—often called charging or inoculating biochar—fills its pores with nutrients and microbial life, allowing it to integrate more effectively into the soil.
Where Is Biochar Used Today?
Research into biochar has expanded rapidly over the last two decades, with applications now being explored across many sectors.
These include:
home gardens and allotments
commercial horticulture
arable farming
forestry
vineyard management
ecosystem restoration
urban landscaping
compost production
livestock bedding and manure management
water treatment
construction materials
Scientists continue to investigate new uses for biochar, making it one of the most versatile materials currently being studied in sustainable land management.
Is Biochar a Solution to Climate Change?
Biochar offers exciting possibilities, but it is important to keep its role in perspective.
No single technology can solve climate change on its own.
Reducing fossil fuel emissions, protecting forests, restoring peatlands, improving energy efficiency, and adopting more sustainable farming practices all remain essential.
Biochar should be viewed as one part of a broader strategy—one that works with natural processes to improve soil health while storing carbon that plants have already removed from the atmosphere.
Its greatest strength lies in delivering multiple benefits at once: healthier soils, greater resilience to drought, support for soil biodiversity, and long-term carbon storage.
Looking Ahead
Biochar is a fascinating example of how ancient knowledge and modern science can come together to address some of today's biggest environmental challenges.
From the fertile Terra Preta soils of the Amazon to cutting-edge research into carbon sequestration and regenerative agriculture, biochar demonstrates that healthy soils are central to a healthy planet.
As research continues, our understanding of biochar will undoubtedly evolve. Yet one thing is already clear: improving the soil beneath our feet may be one of the most effective ways to build a more resilient future.