Sprinkling of Rock Dust May Improve Soil Health and Crop Yield

Adding basalt rock dust to farmers’ fields could help soils to store four times more carbon dioxide (CO₂) and increase crop yields, according to new research by academics at the University of Sheffield.

The study, published in Global Change Biology, found that adding the dust increased yields of the cereal crop sorghum by as much as 20 percent. A single application of basalt enabled the soil to absorb between two and four tons of damaging CO₂ over five years – four times more than untreated soils – suggesting the method also has potential to mitigate the climate crisis.

Removing greenhouse gases from the atmosphere, along with slashing emissions from fossil fuels, is crucial to meeting the Paris Agreement target of limiting global temperature rises to 1.5C above pre-industrial levels. According to the UN’s Intergovernmental Panel on Climate Change, cropland and grassland soil has the potential to store up to 8.6 gigatons of CO₂ per year – equivalent to almost 1.5 times the annual emissions of the United States.

The team of scientists at the University of Sheffield’s Leverhulme Centre for Climate Change Mitigation, affiliated to the Institutes for Sustainable Food and Energy, used the University’s world-class controlled environment facility to conduct the experiments.

Basalt contains at least six nutrients that are essential for plant growth and very low concentrations of toxins. The study found adding it to the soil increased yields of sorghum - the world’s fifth most important crop for food and animal feed – by up to 20 percent. This was achieved without the use of phosphate and potassium fertilizers – making the method suitable for organic farmers.

The basalt also helped to mitigate soil acidification. This is usually treated with agricultural lime – the production of which accounts for two percent of agricultural greenhouse gas emissions in the United States.

The mining, grinding, distributing and spreading of the basalt could effectively reduce the carbon removal rates by 10-30 percent – but the research shows this would still leave the technique as effective as other land management practices designed to address climate breakdown.

Michael Kelland, PhD Researcher at the University of Sheffield and lead author of the study, said: “Our results suggest adding basalt rock dust to fields could help our soils to soak up four times more damaging carbon dioxide from the atmosphere.

“This simple technique could also reduce the need for fertilizers and agricultural lime – cutting carbon emissions and lowering costs for farmers.

“Our study is a first step towards rolling out this climate mitigation method across the cereal fields of Europe and North America. The benefits for our climate, food and soil security could be significant.”

Professor David Beerling, Director of the Leverhulme Centre for Climate Change Mitigation at the University of Sheffield and co-author of the study, said: “These results from controlled environment studies are an important first step towards understanding how a carbon dioxide removal strategy called enhanced weathering might work with basalt, an abundant silicate rock, and croplands.

“Our study used a relatively high application rate of basalt as a ‘proof-of-concept’ test for this carbon dioxide removal approach. Our encouraging findings emphasize the need for large-scale field trials with this rock fertilizer.”

Reference

Kelland et al. (2020). Increased yield and CO₂ sequestration potential with the C₄ cereal Sorghum bicolor cultivated in basaltic rock dust-amended agricultural soil. Global Change Biology. DOI: https://doi.org/10.1111/gcb.15089