Biochar in winemaking: better soil, healthier grapes
The Azores occupy a unique position in the world of wine: the only place in Europe where viticulture takes place on volcanic basalt rock, surrounded by the Atlantic Ocean. The vineyards of Pico — recognised as a UNESCO World Heritage Site — produce the distinctive Verdelho wine, a wine with a saline, mineral character rooted in the island's exceptional soil conditions. But that same soil presents winemakers with significant challenges: high acidity, rapid leaching of nutrients due to intense rainfall, and a limited capacity to retain moisture during dry summers.
Biochar — the carbon-rich material produced by heating biomass in a low-oxygen environment — offers a promising answer to these challenges. And on Pico, the raw material is literally growing on the hillsides: the invasive Pittosporum undulatum, which threatens large parts of the island, provides the ideal biomass for high-quality biochar.
What makes Pico's soil so special — and so challenging?
Pico's vineyards are laid out in a labyrinth of lava rock walls, known locally as currais. These protect the vines from the powerful Atlantic winds and create a microclimate that promotes grape ripening. The soil itself is young, volcanic, and relatively poor in organic matter. pH values typically range between 5.0 and 6.0 — on the acidic side for optimal viticulture.
This acidity limits the availability of essential nutrients such as phosphorus, calcium, and magnesium. At the same time, frequent heavy rainfall rapidly leaches nitrogen and potassium from the root zone. The result: winemakers must fertilise regularly, increasing costs and raising the risk of over-fertilisation.
How biochar improves soil chemistry
Biochar acts as a permanent soil amendment. Its porous structure — comparable to a microscopic sponge — provides an enormous internal surface area to which nutrients and water can adhere. In the context of viticulture, the following effects are most relevant:
Enhanced pH buffering. Biochar typically has an alkaline pH (7.5–9.0), depending on production temperature and biomass used. Adding 2–5% biochar to Pico's soil can gradually raise the pH towards the optimal range of 6.0–6.5, increasing the availability of phosphorus and trace elements without the need for artificial liming.
Improved water retention. Research from Wageningen University demonstrates that biochar can increase the water-holding capacity of light, volcanic soils by 15–25%. For Pico's winemakers, this means reduced irrigation needs during dry summer months and less drought stress for vines during heat waves.
Reduced nutrient leaching. The negatively charged surfaces of biochar bind positively charged ions such as potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺). This significantly slows leaching, reducing the need for fertilisers and decreasing the risk of groundwater contamination.
Stimulation of soil life. Biochar's pores provide a sheltered habitat for beneficial fungi and bacteria, including mycorrhizal fungi that improve root absorption of phosphate and water. In trials with vines in southern Europe, biochar addition led to a 30–40% increase in mycorrhizal colonisation.
From Pittosporum to vineyard: the PicoChar cycle
What makes the PicoChar approach distinctive is the closed loop created when biochar from Pittosporum undulatum is applied in Pico's vineyards. The invasive tree — which threatens local biodiversity and competes with native vegetation — is actively removed and converted into biochar through pyrolysis at temperatures between 450°C and 600°C.
This temperature range produces a biochar with a high content of stable aromatic carbon (>70% C), a well-developed porous structure, and a neutral to slightly alkaline pH — ideal for Pico's acidic soils. Furthermore, the pyrolysis process produces bio-oil and pyrolysis gas, which can serve as an energy source for the process itself, making it nearly energy-neutral.
Applying Pittosporum biochar in Pico's vineyards creates a double benefit: the invasive species is controlled and the soil quality of the UNESCO-listed vineyards is improved. The carbon that Pittosporum captured during its growth is stored in the soil for hundreds of years — a concrete contribution to climate mitigation.
Practical application: dosage and method
For viticulture on volcanic soils, we recommend the following approach:
| Phase | Dosage | Method | Timing |
|---|---|---|---|
| Initial soil improvement | 10–20 t/ha | Incorporate to 30 cm depth | Autumn, before growing season |
| Annual maintenance | 2–5 t/ha | Shallow incorporation or mulching | After harvest |
| Targeted root zone improvement | 5–8 t/ha | Trench method along rows | Early spring |
Important: biochar works best when 'charged' with compost or liquid fertilisers before application. Dry biochar has a high adsorption capacity and can temporarily draw nutrients from the soil in the first weeks after application. Allowing the biochar to mature with compost for 2–4 weeks (ratio 1:3) prevents this effect.
What winemakers on Pico can expect
Based on comparable projects in volcanic wine-growing regions (Canary Islands, Etna region in Sicily), the following effects are realistic after 2–3 growing seasons:
- A measurable improvement in soil pH towards the optimal range for viticulture
- A reduction in irrigation requirements of 10–20% during dry summers
- A reduction in fertiliser needs of 20–30% through improved nutrient retention
- An increase in microbiological activity in the soil, visible as improved soil structure
- Healthier vines with greater resistance to drought and soil-borne diseases
The effect on wine flavour profiles is an interesting area of research. Early results from Italy and Portugal suggest that biochar can enhance the minerality of wines — a quality that would be particularly valuable for Pico's Verdelho.
Conclusion: an investment in the future of Pico viticulture
The combination of an invasive species management challenge and the soil challenges of Pico's vineyards makes biochar an exceptionally fitting solution. PicoChar offers winemakers on Pico an EU-recognised agricultural amendment that structurally improves soil quality, reduces dependence on external inputs, and contributes to carbon sequestration in the soil.
Are you a winemaker on Pico or one of the other Azorean islands and want to know how biochar can improve your vineyard? Contact us for a free consultation or request a free soil analysis.
Sources: Lehmann & Joseph (2015), Biochar for Environmental Management; Glaser et al. (2002), Soil Biology & Biochemistry; Wageningen University, Biochar in Viticulture Research Programme (2021); European Biochar Certificate (EBC) Standards.