29-07-2025
Basalt dust can act to increase soil pH values
An Anglo-French research study has found that dust created by crushing basalt rocks can significantly enhance soil pH values.
The same work also suggests that spreading crushed volcanic rock on farmland could help capture carbon dioxide from the atmosphere — and even boost crop yields — but its success depends on local soil conditions.
Researchers from Rothamsted Research in England and INRAE in Bordeaux, France, along with the UK's National Oceanography Centre, tested the effects of basalt rock dust – a by-product of quarrying – on two types of agricultural soil.
The team applied two different quantities in pot experiments — at the equivalent of 80t/ha and 160t/ha— to both sandy and silty clay soils, monitoring their impact on soil chemistry and ryegrass growth.
The technique, known as 'enhanced weathering', aims to accelerate the natural breakdown of silicate rocks, a process that removes CO 2 from the air and stores it in the soil.
Advocates say the technique could become a valuable tool in tackling climate change while improving soil health.
Soil pH values
The results of the study show that basalt can be an effective soil amendment, especially on nutrient-poor or slightly acidic soils
Specifically, the study found that basalt applications raised soil pH — a key indicator of fertility — by around 0.8 units.
The rock dust also released valuable nutrients like potassium, which significantly increased plant growth in sandy soils.
However, the uptake of some minerals, such as phosphorus and trace metals, declined due to changes in soil chemistry, particularly in soils that were already nutrient-rich.
Rothamsted's Stephan Haefele said: 'These results show that basalt can be an effective soil amendment, especially on nutrient-poor or slightly acidic soils.
'But there is no universal outcome – local soil characteristics play a crucial role.'
The findings highlight the need for site-specific assessments before rolling out enhanced weathering on a large scale. While the approach holds promise for reducing atmospheric carbon and improving agricultural productivity, it is no silver bullet.
However, the research adds to a growing body of evidence supporting the use of rock dust in regenerative agriculture, a practice increasingly seen as a frontline defence in the climate crisis.
Basalt deposits in Ireland are primarily found in counties Antrim and Derry with some occurrences extending into parts of Donegal, Monaghan, and Louth.
These are part of the North Atlantic Igneous Province and were formed during the Paleogene period, specifically around 50-60 million years ago.
The Antrim Plateau comprises a basalt layer that overlies limestone.
