BIOCHAR: FUEL FOR THE SOIL
Órgiva - Andalusia
Imagine one of Europe’s hottest, driest regions, where climate change is accelerating desertification. In Andalusia’s Alpujarra, years of intensive farming have depleted the soil, and traditional practices like burning olive prunings have become risky in a drier climate.
That’s where Sierra Preta, a local non-profit, steps in. Using pyrolysis kilns, they safely burn agricultural waste, turning it into biochar: a charcoal-like substance made at high temperatures with little oxygen.
Biochar helps restore soil by retaining moisture, supporting plant growth, and cutting fertilizer use. It also locks carbon in the ground for centuries, helping fight climate change.
How is biochar produced?
At the heart of Sierra Preta’s work is a flame-curtain pyrolysis kiln: a large, trapezoidal metal container that turns olive prunings into biochar.
The kiln’s angled design (63°) regulates airflow. As the wood heats up, it doesn’t burn completely. Instead, it undergoes pyrolysis: flammable gases rise and ignite at the surface, while the material below is shielded from oxygen and transforms into biochar rather than ash.
This process doesn’t produce ash, but biochar: a charcoal-like material that stores carbon in the soil and improves its structure and fertility over time.
It starts with a small fire at the base of the kiln. Material is added gradually, layer by layer, until full. The oxygen-limited environment keeps emissions minimal: as seen in the photos, there’s barely any smoke. Once the fire reaches the top, it’s extinguished with water. The resulting biochar is dried, bagged, and ready to use — a low-tech, effective, and replicable way to turn waste into value.
How do local farmers get involved?
Sierra Preta offers three options: farmers can join the association (€30/year), rent the kiln, or deliver prunings to the team. In return, they receive a share of the biochar, while the rest is sold to support the project.
Who’s behind the Sierra Preta project?
Founded in Órgiva, at the foot of the Sierra Nevada near Granada, Sierra Preta was started by Lolo and Hanieka, residents of the Cigarrones community in the Río Sucio valley. Since the 1980s, people here have chosen a life rooted in nature, self-sufficiency, and mutual support, rejecting consumerist norms.
But this isn’t just an alternative lifestyle: it’s a concrete effort to regenerate the land. Through Sierra Preta, they promote biochar to restore soil health and help farmers manage agricultural waste sustainably.
The name Sierra Preta is inspired by terra preta, a fertile, carbon-rich soil created centuries ago by Indigenous communities in the Amazon through controlled burning. It remains one of the oldest known examples of soil regeneration: a model that connects traditional knowledge with today’s sustainability challenges.
Education is central to Sierra Preta’s mission. The team trains farmers on biochar’s benefits and how to use the kilns independently. The technology is simple, local, and meant to be shared.
The work of Sierra Preta is a clear example of how innovation can coexist with tradition, offering practical tools to restore the land and build a more resilient future, in balance with nature.