Promising results have been achieved from a trial that applied basalt rock dust to spring oats, and the product is being offered free of charge to farmers in selected parts of the region. It is part of the drive to mitigate the effects of climate change.

A trial at Newcastle University’s Nafferton Farm, near Newcastle, showed an “encouraging” yield response to the application of basalt rock dust, according to Jez Wardman of UNDO. Set up in 2022, the carbon dioxide removal company partners with quarrying companies to spread rock dust on agricultural land in the UK and abroad.

“Our service supplies free basalt rock dust to farms close to designated quarries, and also covers the cost of application,” he said. “This captures CO2 and in return UNDO retains the value of the CO2 captured. It is a slow-weathering product, capturing 5 tonnes of CO2 equivalent over the following two decades, when applied at a rate of 20 tonnes per hectare.

“Basalt rock dust has an alkalising effect and it can help to manage the soil pH, although it should not be used to fully replace standard lime. Alongside the benefits to soil pH, it will also deliver several nutrients over the two decades, including useful amounts of potassium, as well as calcium, magnesium and a number of trace elements. It is approved for use on all agricultural land, including organic farming systems.”

It is early days for the product, but it is expected that application timing will follow a similar pattern to lime and be repeated every three or four years after soil sampling. Most eligible farms are situated along the A1and A68 in Northumberland.

“Our commitment to minimising our carbon footprint means that it is preferable that farms are within a 20-mile radius of the relevant quarries,” said Mr Wardman. “It is possible that the service may be extended to other areas in the future. Basalt rock has already been made available in many parts of Scotland, which also has a number of quarries which produce basalt rock dust as a by-product.”

Nafferton Trial

The trial involved the application of basalt rock spring oats in 2022. Some plots were direct-drilled and others were established using the plough, while the control plots were sown minus the basalt rock dust application. Tissue samples were collected from the plants at the peak of the season, with grain samples collected at harvest time. The soil samples were taken 256 days after the treatment application.

“The spring oat yield was 15 per cent higher overall on the plots where the product had been applied,” reported Mr Wardman. “The yield on the ploughed area was 9.3 per cent higher, with a 20.5 per cent increase for the direct drilled plots. The basalt rock dust also had an effect on soil pH after testing. The results showed an increase of between 0.2 and 0.29 pH units, compared with the control plots.

“Following tissue sampling, plants on the treated soil had higher concentrations of calcium, as well as grain and tissue potassium. This indicates the potential value of the product in terms of boosting crop nutrient availability, and it may improve crop yields. No toxic elements were found on the treated plots after analysis, and it had no negative impact on the natural environment.

“I was expecting enhanced performance where the basalt rock dust had been applied, but I was surprised that the results showed such a significant yield increase. The 2022 sowing season was unusually dry and plant root systems were sub-optimal in many cases. The additional potassium and other nutrients, coupled with the positive effect on soil pH, may have had a more marked influence compared with a normal year.”

Basalt rock dust

Basalt rock dust is a finely crushed silicate rock which is a by-product of the processing operation in quarries used to make asphalt and roadstone. Each particle measures less than 4mm and it is unaltered from the production phase to its journey from the quarry to the farm in wagon loads.

‘Rock weathering’ is the terminology used to describe the natural process which occurs when rainwater meets natural rock, explained Mr Wardman.

“The effect happens when CO2 in the atmosphere is dissolved in rainfall. It forms a weak carbonic acid, which gradually wears away the rock when it rains. This results in the formation of soluble form of carbon called bicarbonate ions, which capture carbon.

“This carbon capture can take many thousands of years if left to nature. However, the ‘enhanced’ rock weathering crushes the basalt, greatly increasing the surface area. This accelerates the carbon capture process when the product is spread on land. It plays a valuable role in mitigating the effects of climate change, because it acts as a nature-based carbon removal process.”