What Is Biochar
Biochar is a carbon-rich material similar to charcoal that is made by heating organic materials - such as crop residues, wood, bamboo, manure, or other plant-based matter - in a low-oxygen environment, a process known as pyrolysis. The term biochar is used to distinguish it from charcoal when it is prepared for use as a soil amendment, for storing soil carbon, managing organic waste, or recovering energy. Interest in biochar has grown rapidly as farmers and policymakers seek ways to build long-term soil health while also addressing climate change.
The scientific literature on biochar now spans decades and thousands of studies. When incorporated into soil, biochar can influence key properties such as pH and nutrient retention, soil structure, and overall carbon content. In some systems, these changes improve crop performance; in others, they do not. Outcomes vary widely depending on soil type, climate, feedstock chemistry, application rate, and experimental design, making biochar a highly context-dependent amendment. This variability is emphasized in studies exploring global response variability and in work examining how soil constraints govern site-specific performance.
This process of making charcoal, called pyrolysis, converts living or once-living organic matter into a stable, carbon-rich material with a highly structured form. Unlike most organic matter, which breaks down relatively quickly in soil, biochar can persist for decades or longer. Because of this long lifespan, biochar is often described as a way to store carbon in soils rather than releasing it back into the atmosphere.
This series explores the scientific evidence of biochar for agriculture and climate mitigation, with a focus on conditions relevant to temperate agricultural systems like ours in the Northeast United States.
How We Got Interested
Like many people, we first encountered biochar through the story of unusually fertile, charcoal-rich soils in the Amazon basin known as Terra Preta de Índio. These “dark earth” soils contain elevated levels of stable carbon and nutrients compared to surrounding highly weathered tropical soils. Radiocarbon evidence suggests these soils developed over long periods of human occupation, with charcoal fragments forming a durable component of their carbon profile.
Early interpretations suggested that intentional charcoal additions contributed to long-term soil fertility and carbon persistence. That interpretation inspired interest in biochar as a modern analog. However, more recent research has emphasized that Terra Preta soils likely resulted from a complex combination of geomorphic processes (e.g., alluvial sediment deposits) and anthropomorphic impacts (e.g., charcoal and human waste deposition) over long time periods.
The Terra Preta story remains important. It demonstrates that human management can influence soil carbon over long time horizons. It does not demonstrate that applying biochar can replicate those soils, especially over the short-term.
From Early Farm Use to Formal Research
When we began Arthur’s Point Farm, we were working with soils that had experienced years of conventional use and exhibited low organic matter and nutrient limitations. Biochar appeared to offer a way to rebuild soil carbon while potentially improving nutrient retention and water-holding capacity. We were also motivated by its potential as a natural climate solution.
We purchased a retort kiln and began producing biochar on-site using downed wood and cutoffs from a local mill. Over time, we incorporated biochar into our compost systems, nursery beds, tree planting rows, and potted nursery production. Compost is a well-established soil amendment with documented effects on soil structure, nutrient supply, and plant growth. Our early experience suggested that compost produced visible plant responses, but the independent contribution of biochar was less clear.
That uncertainty led to more formal inquiry through a USDA Sustainable Agriculture Research and Education grant. The results form the basis of this web series.
