Discovery and history
When people talk about biochar today, it can sound like a cutting-edge innovation against climate change and soil degradation. But its roots reach far into the past—a fascinating story of observation, tradition, and rediscovery.
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Terra Preta – the legacy of Amazonian cultures
Across the Amazon there are areas that long puzzled soil scientists: Terra Preta do Índio—“black earth of the Indigenous.” These soils are dark, friable, extremely fertile, and rich in charcoal particles. In a region where native soils are often nutrient-poor and easily leached, Terra Preta seems like a contradiction. Its remarkable fertility has remained stable for centuries, resisting the heavy tropical rains that usually wash nutrients away.
Archaeological evidence shows these soils did not arise by chance but through deliberate human practice. Over long periods, Indigenous communities mixed charred plant residues with organic wastes like food scraps, animal bones, manure, ash, and even pottery shards. The result was a stable, nutrient-rich habitat for plants and microorganisms. This knowledge was passed down through generations—a quiet yet remarkably effective cultural technique.
Early scientific attention in the 19th and 20th centuries
European explorers and missionaries reported unusually fertile Amazonian soils as early as the 19th century, but systematic study began in the 20th. Dutch soil scientist Wim Sombroek published Amazon Soils in the 1960s, describing Terra Preta’s extraordinary properties and proposing that these were human-made soils—a revolutionary idea that challenged the prevailing notion of soils as purely “natural” systems.
Sombroek’s work inspired a generation. In the following decades, researchers like Johannes Lehmann, Bruno Glaser, William Woods, and Eduardo Neves combined archaeology, soil science, and ethnology to trace Terra Preta’s origins. Lehmann’s work at Cornell University in the early 2000s was pivotal in linking traditional practice with modern soil science.
From old knowledge to a global movement
As Terra Preta research grew, it became clear that the principle—pyrolyzing biomass, stabilizing it in soils, improving fertility—could be replicated worldwide. Researchers experimented with wood, rice husks, corn cobs, and nut shells. At the same time, the climate benefits came into focus: once charred, biomass no longer releases its carbon quickly as CO₂ but locks it away for centuries.
Around this time the word “biochar” emerged—a blend of “biological” and “charcoal”—to distinguish it from barbecue charcoal and emphasize its agronomic and scientific context. By 2006/2007 the International Biochar Initiative (IBI) had formed, and continues to advance research, standards, and networking.
Traditions beyond Amazonia
While Terra Preta is the best-known example, similar practices existed elsewhere. In Japan, “sumiyaki” has for centuries involved adding small amounts of plant charcoal to agricultural soils. In parts of West Africa, ash and charred residues have been integrated into farming systems. These parallels show how deeply rooted the idea is: using fire and charcoal not only as fuel, but as a soil improver.
Rediscovery in the 21st century
Today biochar is studied globally—from small garden projects to industrial-scale plants. The historical thread runs unbroken from Indigenous practices in Amazonia, through 20th-century soil science, to the present. Biochar’s “discovery” is less an invention by any single person than a rediscovery and refinement of ancient knowledge that has gained new meaning in the light of modern climate and agricultural research.
What is biochar
Biochar—known in German as Pflanzenkohle—is produced by heating organic material without oxygen, a process called pyrolysis. The biomass doesn’t burn; it carbonizes. Typically this happens between 350 and 700 °C. The end product is a highly porous, black carbon that differs chemically and physically from ordinary charcoal.
Unlike fuel charcoal, biochar is designed to improve soil. Its countless micro-pores act like a sponge, storing water and holding plant-essential nutrients. These pores also provide habitat for microbes. In this way, biochar becomes a hub in the soil—retaining nutrients, buffering moisture, and offering shelter for soil life.
Chemically, biochar is very stable. Fresh plant residues decompose quickly and release CO₂, but biochar can persist in soils for centuries or even millennia. Stability depends in part on production temperature: higher temperatures create more condensed, resilient carbon, while lower temperatures tend to yield surfaces that interact more with nutrients.
Feedstocks matter too. Wood, straw, nut shells, rice husks, and corn cobs each produce chars with distinct traits. Wood-based chars often have larger, structure-stable pores; agricultural residues can yield finer structures with higher cation exchange capacity. “Biochar” is thus an umbrella term—performance depends strongly on the feedstock and process.
For soils, this means biochar is not a classic fertilizer. It doesn’t supply large immediately available amounts of N, P, or K on its own. Its strength is to hold nutrients introduced via compost, manure, or fertilizers and release them gradually. Think of it as a nutrient buffer that stabilizes the soil environment. It also helps retain moisture—especially valuable in light, sandy soils where water leaches quickly.
Biochar can influence soil pH as well. Often slightly alkaline, it can temper acidic soils—useful in regions facing acidification from rainfall or intensive agriculture.
In short, biochar is far more than “burnt wood.” It’s a natural, high-performance material that permanently improves soil properties, supports soil life, and serves as a long-term carbon store.
Making biochar – three approachable methods
1. Slow pyrolysis
This is the industrial approach. Biomass (e.g., wood, straw, nut shells) is heated in large kilns for hours. Without oxygen it doesn’t burn, it carbonizes. Alongside biochar, usable gases and oils are produced, for energy or as feedstocks.
In a nutshell: plants go into a big oxygen-free “oven” and come out as both char and energy.
2. TLUD stoves (Top-Lit UpDraft)
Robust metal tubes or larger metal containers—such as ducting or food-grade pails—are used to build a compact pyrolysis stove. Key point: a minimum diameter of about 10 cm (4″), ideally 15 cm (6″) so air can flow and wood gases burn cleanly. You light the biomass at the top; the flame front slowly moves downward. The gases burn cleanly above while char forms below. You quench with water at the end.
In a nutshell: a small, top-lit stove that gives you a clean cooking flame above and finished biochar below.
3. Kon-Tiki or flame-curtain kilns
You work in a conical pit or metal cone. Start a small fire at the bottom, then add biomass in layers on top. The geometry pulls the flame upward and combusts gases immediately, keeping smoke low. Lower layers char while fresh material on top burns. Finally, quench the char with water.
👉 A Kon-Tiki lets you turn prunings, brush, and wood scraps into substantial amounts of clean biochar without expensive gear.
A fire that leaves more than ash
When we made our own char, it honestly felt like a giant campfire—just deeper and more deliberate. We dug the pit extra deep so we could build up enough layers. We’d collected material for weeks: lots of deadwood that had once protected the soil under heavy clearing machines. Using it now solved two things at once—tidying and freeing a piece of the property, reducing fire risk from drying wood, and producing valuable biochar. Layer by layer we added wood, watched the flames dance, listened to the crackle—almost like sitting by a fire, but with the sense that something lasting was forming: char that would gift our soil with fertility for years.
Why “charging” matters
Fresh biochar is empty at first—no nutrients, just surface and pores. If you add it straight to soil, it can soak up nutrients that plants might need.
Charging means pre-filling the char with nutrients and microbes before it touches the garden. There are several ways:
- With compost: mix char into the compost heap. Through decomposition it absorbs nutrients and soil life, becoming a “nutrient reservoir.”
- With manure: blend biochar with animal manures. The pores take up nitrogen and other nutrients.
- With liquids: soak biochar in diluted urine, compost tea, or homemade ferments (e.g., comfrey brew). These liquids infiltrate the pores and “load” them.
Prepared this way, biochar behaves not as a nutrient thief but a nutrient source, slowly releasing fertility over time while offering a home for microorganisms.
When char comes to life
We didn’t put char straight into the beds—we fed it first. In large bins we mixed water, urine, compost tea, and comfrey brew. For several weeks the char soaked; we stirred it regularly and topped up nutrients. You could literally smell the process: sharp at first, then gradually neutral, earthy, alive. That’s how we knew it was ready. Only then did it go into our beds—as a reservoir that lifts soil life instead of holding it back.
Research – effects and potential
Yield gains
In tropical, nutrient-poor, or sandy soils, biochar acts like a water-holding sponge that also keeps fertilizers from leaching. Jeffery et al. (2017) analyzed 100+ studies and found average yield increases around 25%. The effect is most visible under drought or heavy rain. Even in more fertile European soils there’s value—stabilizing yields and buffering heat-stress summers by improving water retention.
Climate benefits
Biochar is extremely stable. Crombie & Mašek (2013) show that higher pyrolysis temperatures create aromatic carbon structures that resist decomposition for centuries. That makes biochar a true carbon sink—carbon stored in soil instead of released as CO₂. It’s one of the few approaches that couples farming with long-term carbon removal.
Lower greenhouse gases
Nitrous oxide (N₂O) is a powerful greenhouse gas—up to 300× CO₂. Studies such as Cayuela et al. (2014) and Kaur et al. (2023) show biochar can cut N₂O emissions by 30–50%. Mechanisms include changes in soil physics and the microbiome, leading to fewer gaseous losses and more retained nitrogen—especially valuable in intensively fertilized soils.
Soil life
Han et al. (2023) show biochar strengthens microbial communities. Its pores become habitats for bacteria and fungi—particularly useful under drought, because tiny reservoirs of moisture and shelter remain in the char. The result is a more resilient soil food web that supports plants better.
Limits & risks
Spokas (2010) cautions that biochar won’t do much in already fertile clay soils. Fresh, uncharged char can even cause startup losses by tying up nutrients. Poor processes (smoldering, PAH formation) pose risks too. In short, how biochar is made and used matters as much as the fact that it exists.
Application – when & how to get biochar into the soil
When?
Spring: Best only with pre-charged char so plant growth isn’t suppressed. Young crops benefit immediately without nutrient drawdown—heavy feeders like tomatoes or brassicas respond especially well.
Autumn: Char has the winter to become colonized by microbes. Combined with fall compost or mulch, it sets the stage for a particularly fertile spring.
How?
- Top-dress & work in: Broadcast biochar and lightly rake or cultivate it in. The finer the pieces, the more evenly it spreads. In sandy soils you’ll notice real gains in water-holding.
- Build it into beds: When establishing new beds—raised or hugelkultur—work pre-charged char into the rooting zone from the start so it can bind and re-release nutrients immediately.
- No-till gardening: In systems without digging, sprinkle biochar into the mulch or top compost layer. Rain, earthworms, and microbes gradually carry it down. It’s the gentlest, most soil-friendly method.
- Raised beds: Biochar serves as a long-term component, preventing nutrient leaching low in the profile and stabilizing moisture—great when raised beds dry out fast in summer.
- Hugelkultur mounds: Highly effective, as char works together with buried wood and organic matter, buffering moisture and nutrients while upper layers decompose.
- Containers and pots: Biochar improves water retention—especially helpful in hot spells when containers dry rapidly—keeping conditions more even for roots.
- Agroforestry alleys: Incorporated along tree and shrub rows, biochar steadies soil structure over the long term and supports deep roots with more consistent moisture and nutrients.
- Vineyards and orchards: Char can loosen compacted soils, raise water-holding capacity, and support perennial vigor over years.
These images powerfully show how vigorously the shrubs planted in our soil-biochar mix have developed—from first shoots to robust bushes with abundant fruit. We were harvesting in the first, at the latest the second year. We explain how we built the beds in detail here: What is Homesteading?
Thoughts by the fire
When we think back to our first “Kon-Tiki campfire,” it was more than an experiment. It was an evening of crackling flames, steaming embers, and the realization that something new can grow from seemingly useless deadwood: a treasure for our soil. For us, biochar is not just a research topic, but a tool that brings together ancient knowledge, modern science, and the joy of gardening.
Every layer of char we spread was a step toward more living soil, less reliance on synthetic fertilizers, and more resilience in our plants. And we know this too: every bit of carbon that stays in the ground is a small contribution to the climate.
Maybe your journey starts with a tiny TLUD stove, or with a few shovels of char in a raised bed. Maybe it becomes a larger project with compost, manure, and fully charged biochar. However small the beginning—it’s a beginning. And the wonder of char is that it lasts.
References
Cayuela, M.L. et al. (2014): Biochar’s role in mitigating nitrous oxide emissions. Agriculture, Ecosystems & Environment.
Crombie, K., Mašek, O. (2013): Pyrolysis characteristics and stability of biochar. Biomass & Bioenergy.
Glaser, B., Woods, W.I., Lehmann, J. (2004–2009): Sammelbände und Artikel zu Terra Preta und Biochar.
Han, Z. et al. (2023): Biochar effects on soil microbial communities. Frontiers in Environmental Science.
Jeffery, S. et al. (2017): Meta-analysis of crop yield response to biochar. Agriculture, Ecosystems & Environment.
Kaur, G. et al. (2023): Biochar and greenhouse gas mitigation. Science of the Total Environment.
Lehmann, J., Glaser, B. et al. (2003–2007): Biochar for environmental management. Cornell University.
Rittl, T.F. et al. (2021): Biochar reduces N₂O emissions in agricultural soils. Global Change Biology Bioenergy.
Sombroek, W. (1966): Amazon Soils.
Spokas, K. (2010): Review of biochar research and uncertainties. Sustainability.
Woods, W.I. et al. (2009): Amazonian Dark Earths: Origin, Properties, Management. Springer.
