Biochar and Terra Preta: Ancient Soil Wisdom for Modern Farmers
- Joshua Brock
- 3 hours ago
- 7 min read
For thousands of years, farmers have been trying to answer the same question: how do we build soil that lasts? Today, one of the most promising answers comes from an ancient practice rediscovered for modern times — biochar.
From small organic growers to large commercial operations, farmers are turning to biochar to improve soil fertility, hold more water, and store carbon long-term. And the story of biochar begins deep in the Amazon, with the mysterious and remarkably fertile soils known as terra preta.
Let's take a quick look at the topics we'll cover in this article:
What Is Biochar?
Biochar is a form of charcoal made from plant and animal materials — wood chips, crop residues, manure, and other biomass — that are heated in a low-oxygen environment. This process, called pyrolysis, converts organic matter into a stable, carbon-rich substance that looks like fine black charcoal.
Unlike ashes from a fire, which are mostly minerals, biochar retains the carbon structure of the original material. When added to soil, it improves its ability to retain moisture, hold nutrients, and support microbes.
You can think of biochar as a long-term home for carbon and microorganisms — one that keeps on giving for decades, even centuries.
The Ancient Origins: Terra Preta of the Amazon
Centuries before modern soil science existed, the Indigenous peoples of the Amazon Basin were already enriching their nutrient-poor tropical soils using a method that scientists only recently began to understand.
They created what we now call Terra Preta, or “dark earth.” These soils, often several feet deep, are rich, black, and incredibly fertile — still supporting crops more than 1,000 years after their creation.
What makes Terra Preta so unique?
It contains high concentrations of biochar, along with compost, fish bones, pottery shards, and organic waste.
It holds three to five times more organic carbon than surrounding soils.
It continues to regenerate microbial life and fertility even after centuries.
In essence, Terra Preta is the living proof that biochar can build soil that lasts for generations. Modern biochar practices are inspired by these ancient methods — updated with scientific understanding and modern equipment.
Why Biochar Works: Key Benefits for Farmers
There are a variety of benefits for farms that incorporate biochar into their soil and sustainability practices. Let's take a look at the five most prominent ones.
Better Water Management
Soil moisture is one of the most important factors in crop performance — too little water stresses plants, too much reduces oxygen to roots. Biochar helps moderate both extremes.
Because of its honeycomb-like, porous structure, biochar acts like a moisture reservoir in the soil. In sandy soils, which drain quickly and struggle to hold water, biochar helps capture and store moisture that would otherwise be lost. This means crops can go longer between rains or irrigation cycles without stress. In heavy clay soils, which retain water but can become compacted and oxygen-poor, biochar creates micro-channels that improve aeration and root penetration. Water drains more evenly, reducing root rot and compaction issues.
For farmers in drought-prone areas, biochar can be especially valuable. Fields treated with biochar often show:
Better drought resilience
More consistent crop quality
Reduced irrigation frequency
Over time, these moisture improvements can make fields more resilient to shifts in weather patterns and climate extremes.
Nutrient Retention and Fertilizer Efficiency
Fertilizer is one of the most expensive inputs on the farm — and one of the easiest to lose. Nitrogen and other nutrients are highly mobile and often leach out of the soil during heavy rainfall or irrigation. Biochar helps hold nutrients in place.
Its porous structure and high cation exchange capacity (CEC) allow it to absorb nutrients like:
Nitrogen (N)
Phosphorus (P)
Potassium (K)
Calcium and magnesium
Trace minerals
Instead of being washed away, these nutrients remain in the root zone, where plants can gradually draw from them. This leads to improved fertilizer efficiency (your applied nutrients go further), lower fertilizer requirements over time, and reduced runoff into waterways.
For farmers managing manure or compost systems, biochar can capture nutrients during composting, reducing ammonia loss and improving compost quality. In short, biochar helps keep the fertility where you paid to put it — in your soil.
A Boost for Soil Life and Microbial Activity
Healthy soil is not just dirt; it’s a living ecosystem. Beneficial microbes, such as bacteria, fungi, actinomycetes, and soil nematodes, are essential for breaking down organic matter, cycling nutrients into plant-available forms, building soil structure, and supporting plant immune systems.
Biochar provides an ideal habitat for these organisms. Those microscopic pores create protected spaces where microbes can attach, reproduce, and form stable communities.
This is part of why biochar must be charged before use. Once filled with compost, manure tea, or fertilizers, biochar becomes a microbial hotel, storing both nutrients and life.
Over time, increased microbial activity leads to:
Better nutrient cycling
Enhanced root growth
Stronger rhizosphere (root-soil) relationships
More disease-resistant plants
This is the foundation of regenerative soil health!
Long-Term Carbon Storage and Climate Benefits
Most organic matter — crop residues, manure, plant roots — eventually decomposes, releasing carbon dioxide (CO₂) back into the atmosphere. Biochar is different. Pyrolysis converts carbon into a highly stable form that resists decomposition. When added to soil, this carbon can remain locked in place for hundreds to thousands of years.
This means every batch of biochar applied to soil permanently removes carbon from the atmosphere. Farmers can contribute directly to carbon sequestration — something once limited to forests and grasslands. In some regions, farmers are now earning carbon credits for biochar use — a potential future revenue stream as carbon markets expand.
But even without carbon incentives, the agronomic benefits alone make biochar a worthwhile investment.
Improved Crop Yields and Plant Health
Biochar doesn’t behave like a traditional fertilizer — it doesn’t “feed” crops immediately. Instead, it improves the soil environment, which allows plants to grow more efficiently and withstand stress better.
Farmers who use biochar commonly report:
Higher germination rates
Improved root development
Greater drought tolerance
More consistent yields across variable weather years
Additionally, biochar can buffer soil pH, reducing acidity in low-pH soils and allowing crops to access nutrients previously “locked up.” In highly weathered or depleted soils, this can be a game-changer. The result is a field that is more productive, resilient, and economical to manage over time.
Just like the ancient terra preta soils still producing crops today, biochar doesn’t “burn out.” It continues to support fertility year after year.
How Biochar Is Made
Feedstocks
You can make biochar from almost any dry organic material, including:
Wood chips or sawdust
Corn stalks, rice husks, or other crop residues
Animal manure
Nut shells or fruit pits
Avoid any feedstock that contains plastics, paints, or treated materials.
The Process (Pyrolysis)
Pyrolysis means heating biomass in the absence of oxygen. This can be done using:
Pit or trench kilns – simple, low-cost methods suitable for on-farm use.
Cone or barrel kilns – portable systems that provide better temperature control and consistency.
Commercial pyrolysis units – larger-scale systems that can also capture byproducts like bio-oil and syngas.
From left to right:
trench kiln (courtesy: naturechange.org)
barrel kiln (courtesy: appropedia.org)
cone kiln (top right | courtesy: thebiocharrevolution.com)
CharBoss air curtain incinerator (bottom right | courtesy: fs.usda.gov)
If you’re experimenting for the first time, start small with a cone kiln or barrel system.
Charging or Inoculating Biochar
Fresh biochar is like an empty sponge — ready to soak up whatever it can find. If applied directly to soil, it can absorb nutrients meant for your plants, temporarily reducing fertility.
To prevent that, farmers “charge” or “inoculate” biochar by pre-loading it with nutrients and microbes. You can do this by:
Mixing biochar with compost and letting it sit for a few weeks
Soaking it in manure slurry, compost tea, or liquid fertilizer
Combining it with worm castings or microbial inoculants
Once charged, biochar is ready for use and will begin supporting soil life immediately.
Applying Biochar on the Farm
Application rates vary by soil type and crop, but general guidelines include:
1–10 tons per acre for broad-acre crops
5–20% by volume in garden beds or potting mixes
Biochar can be incorporated into the topsoil, mixed with compost or manure, or even added during tillage or planting. Once it’s in the soil, it stays there — continuing to improve conditions year after year.
Bringing Ancient Wisdom Into Modern Practice
What makes biochar truly remarkable is how it blends ancient knowledge with modern sustainability goals. The Indigenous farmers who created terra preta weren’t thinking about climate change or carbon credits; they were finding ways to turn waste into fertility.
Today’s farmers can do the same. By producing biochar from crop residues, pruning waste, or manure, you can build richer and more resilient soils, reduce fertilizer and irrigation needs, turn waste streams into valuable soil amendments, and sequester carbon in the process.
It’s a solution that’s regenerative by design — restoring soil health, improving productivity, and helping address global challenges.
The Bottom Line: "It's In There!"
Biochar isn’t a quick fix, but it is a powerful long-term investment in soil health. Just as the terra preta soils of the Amazon have endured for millennia, the biochar you add today can continue benefiting your land for generations to come.
Whether you farm a few acres or a few thousand, biochar offers a chance to reconnect with a simple truth: Healthy soil is built, not bought — and sometimes, the best ideas are the oldest ones.
Joshua, his wife Jenn, and their dog Rooster live in PA. Joshua is the owner and operator of Hoffman Appalachian Farm, where they grow Certified Naturally Grown hops. Joshua has over twelve years of experience in growing crops, including growing in an organic system. In his spare time, he enjoys trail running, backpacking, and cycling.