Machine spreads rock dust on fields
Photo: UNDO/ Newcastle University
By Gary Hartley

Volcanic rock dust boosts yield, soil pH and crop nutrients in UK trial

Adding volcanic rock dust to arable soils in temperate climates like the UK’s could be a sustainable way of boosting yields, raising soil pH levels and helping agriculture reduce its carbon footprint.

A project exploring the application of volcanic rock dust to farmland aw average yield increases of 15% in just a year, as well as elevated soil pH levels — a change that enables crops to access more soil nutrients.

In a first-of-its-kind study in the UK, carbon dioxide removal company UNDO teamed up with Newcastle University and its Nafferton Farm site to test the effects of applying 20 tonnes per hectare of finely crushed basalt on fields growing spring oats under two different cultivation programmes.

The soil carbon sequestration benefits of adding volcanic rock dust to soils are increasingly well known: A 2020 Nature paper made the case for enhanced weathering to play a large role in CO2 removal on the world’s croplands. Meanwhile, more recent work has underlined that the approach could work under any climate conditions, even extreme drought, and that multiple benefits can be seen when silicates from volcanic sources are used on saline soils.

Adding to evidence

The Newcastle research sought to build on this evidence base by exploring its effects on yield and soil pH when applied to a typical UK crop. The team collected grain samples during harvest and soil samples 256 days after the basalt was applied, and in results published in the journal PLOS ONE, they found that yield was on average 15% higher (9.3% and 20.5% between ploughed and plots using direct drilling respectively).

Soil pH was 0.2 and 0.29 units higher in the basalt-amended plots compared to controls where the material was not applied — an effect due to alkaline products being generated as the rock minerals dissolve.

Basalt rock releases nutrients during dissolution, and the researchers found higher tissue concentrations of calcium, grain and tissue potassium in the crops grown when they applied rock dust.

Supplying plant nutrition

Jez Wardman, an agronomist for UNDO, said the study’s results are a result of the volcanic dust helping plants to meet their nutritional requirements from the soil.

“There’s nothing magic happening here,” he said. “At the site in Newcastle, something was holding the crop back, something of that interaction within the crop’s roots and the soil.

“Maybe there wasn’t sufficient nutrition in the soil already, or the nutrition wasn’t available, maybe there were issues with weather conditions and establishment, meaning the roots weren’t functioning as well as they could,” he said.

“Something that we did actually improved that. I think that’s the key thing to understand where the yield responses come from.”

The team acknowledge that results won’t be identical in every farm setting and are carrying out additional trials at a range of other sites in the UK. Further work using basalt is also ongoing on the fields of Nafferton Farm, including a new trial looking at regenerative methods of lupin production for homegrown proteins.

Chief Agronomist Jez Wardman of UNDO surveys spring barley crop. Photo: Courtesy of UNDO

Carbon markets change picture

While there’s mounting evidence pointing to the benefits of rock dust in arable systems, and a small group of proponents have been using it for decades, it hasn’t broken through into mainstream farming yet.

UNDO believes that its business model — where farmers stand to gain soil fertility and yield benefits at no up-front cost, while the company is compensated via voluntary carbon credit schemes — can widen the appeal to farmers.

“Going back perhaps even 20 years, farmers were buying the material themselves because they could see the benefits in terms of the nutrients that were released from it. What’s changed recently is the economics of the carbon capture side of things,” said Wardman.

“We’re capturing one tonne of carbon for every four tonnes of rock dust that we’re applying and in today’s carbon market, that changes the whole thing.

“Rather than the farmer actually having to put their hand in their pocket to buy this, the model that we’re taking to the farmers is that what we’re supplying the material to the farmer free of charge.”

Low risks, existing infrastructure

Rock dust available for cropland is a by-product of the mining and quarrying industry. When using materials from a particular quarry, they are first thoroughly tested, explained Wardman. The trial underlined there were no additional toxic elements taken up by crops in the plots where basalt had been spread – a concern that could be another barrier to uptake.

“We believe [widespread application of rock dust] is scalable because everything already exists, nothing new needs inventing or investing in. The quarries, the infrastructure to haul from the quarries to the farm to spread the material, and the land which can benefit from being spread on are all there,” Wardman continued.

Evolving challenges for farmers, as well government incentive schemes for regenerative practices and the National Farmers’ Union’s 2040 net zero target, have increased interest in investigating new approaches, said James Standen, Nafferton Farm director.

In the case of rock dust, the large-scale and professional approach of organisations like UNDO has added to its appeal, as compared to earlier days when the product was sold in dumpy bags.

“Rock dust certainly is not going to be the only product farmers use. It will be one of the range of products they use within a season or over a rotation,” added Standen. “I think that that’s what they need to build in, so hopefully this sort of data will help them.”

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