Volcanic rock dust is gaining attention in agriculture as researchers test whether finely ground basalt can improve soil pH, nutrient availability and longer-term soil resilience.
Field trials in several countries are beginning to build an evidence base, including a UK study showing that applying around 20 t/ha of basalt increased yields by about 15% and lifted soil pH.
As more trials emerge, questions are emerging about availability, cost, application rates and whether the material can realistically support crop performance at commercial scale. This Q&A looks at what is known so far — and where the uncertainties still lie.
What exactly is volcanic rock dust?
Volcanic rock dust, generally made from finely ground basalt, is a mineral-rich powder produced by crushing and milling volcanic rock. Basalt is widely available and naturally rich in calcium, magnesium, potassium, silicon and a suite of trace minerals. Once applied to soil, it gradually releases these nutrients through weathering. Research has shown increases in plant-available Ca, Mg and Si within roughly two years of application.
How does it work in the soil?
Basalt’s main effects are tied to nutrient release and pH moderation. Because it contains Ca and Mg, it can behave somewhat like a mild liming material, helping to raise soil pH and improve nutrient availability.
It also has potential for managing carbon. When basalt weathers, it reacts with COâ‚‚, forming bicarbonates or carbonates in soil water. Research into enhanced rock weathering suggests that large-scale use could contribute to carbon sequestration, although the accounting and verification framework is still evolving .
Weathering rates depend on particle size, soil type and climate. Finer particles release nutrients more quickly, and wetter, temperate environments tend to accelerate the process.
What does the research show so far?
Studies vary, but several consistent themes are emerging. Field trials in temperate agricultural soils have shown yield improvements, pH increases, and better nutrient uptake without evidence of heavy-metal accumulation in crops. Some trials have reported significant changes in soil chemical attributes – particularly calcium, magnesium and silicon – within 22 months. However, effects on potassium availability are inconsistent, and responses tend to be stronger in acidic or low-fertility soils.
There is also growing interest from producers looking to reduce fertiliser costs. Trials in Australia, for example, are examining basalt’s potential to offset high fertiliser prices. Overall, evidence is positive but still limited by the number of long-term, multi-year trials.
How widely is it used, and how big is the market?
Volcanic rock’s use in mainstream agriculture is currently limited, and while the value of the market is expect to increase, for now it is likely to remain a niche product.
The market was worth around USD 58 million in 2024, with projections suggesting it could reach USD 111 million by 2033. For comparison, global fertiliser markets run to tens of billions of dollars, which shows how early-stage basalt adoption still is. Most commercial use today is found in regenerative and organic sectors, horticulture, and research-led farming businesses.
How available is volcanic rock dust, and what does it cost?
Basalt is geologically abundant and quarried widely. Many suppliers in the UK and Europe already produce fine basalt powders for agriculture and horticulture. Availability is generally good, though product fineness varies and costs depend heavily on source proximity.Â
How is it applied, and which soils benefit most?
Most research trials use 10–40 t/ha, with 20 t/ha being common. It can be spread with standard lime or fertiliser equipment, although the bulk means multiple loads for larger farms.
Basalt tends to perform best in acidic soils, where its liming effect is strongest. Sandy soils with low nutrient-holding capacity may also respond well. Heavy clays or alkaline soils often see slower changes. Climate matters too: wetter regions typically achieve faster weathering.
Farmers should also check mineral profiles and trace-metal concentrations, as not all basalt sources are identical. Studies so far indicate low risk, but verification is important.
Can it be a substitute for fertiliser or lime?
Only partially. Basalt releases nutrients slowly, so it cannot replace nitrogen or fast-acting fertilisers. It may help reduce the need for lime in some situations, and it can contribute useful micronutrients and silicon, but nutrient management programmes still need to be balanced alongside it.
Most growers trialling basalt treat it as a long-term soil-health amendment rather than a direct fertiliser substitute.
What should farmers consider before trying it?
A small on-farm strip trial is the safest route, ideally spanning multiple seasons to capture slow-release effects. Monitoring should include soil pH, calcium, magnesium and silicon levels, alongside yield responses and any changes in fertiliser requirements.
Cost calculations must include spreading and haulage. Because the material is bulky, farms far from basalt quarries may struggle to justify the economics.
Long-term benefit is the key question: improving soil structure and pH can pay off, but not every farm will see an immediate yield return.
Key facts
- Basalt rock dust supplies calcium, magnesium, silicon and trace minerals through slow weathering.
- Field trials have reported yield gains and pH increases at application rates around 20 t/ha.
- Benefits tend to be strongest in acidic or low-fertility soils where pH and mineral availability are limiting.
- Transport often represents the largest share of total cost due to high tonnage per hectare.
- Commercial use remains limited, with a global market value of about USD 58 million in 2024.
