Could ‘glacial flour’ boost crops – or poison farmers? Maybe both.

The combined challenges of a growing human population, environmental degradation and rapid climate change have sent researchers scrambling to find alternatives to artificial fertilisers.

Using ground-up rock to fertilise fields is one potential solution, and nothing grinds rock more efficiently than giant glaciers scraping their way down mountainsides and across valley bottoms.

Best of all, previous research indicates that using rock dust - ‘glacial flour’ - released by glaciers as fertilizer could boost crop yields and at the same time remove large amounts of carbon from the atmosphere.

Some scientists have proposed shipping huge amounts of glacial flour from Greenland to farmers in Africa and beyond to help to feed the world and meet global net-zero goals.

Toxic soybeans

New interdisciplinary research led by a postdoctoral researcher affiliated with the iC3 Polar Research Hub suggests that policy makers should proceed cautiously with such plans. 

The team of researchers collected glacial flour from two sites, one in Iceland and the other in the Himalayas and used it to fertilise soybeans, one of the most commercially valuable and widely cultivated global crops.

Following application of glacial flour to the soil, the team found that soybean crop yields roughly doubled, photosynthesis and plant stress levels were improved, and the beans had greater nutritional value.

Glacial flour achieved these effects by acting as a source of nutrients and micronutrients to the soybeans.

However, although the yields were better, the beans fertilized with Himalayan flour accumulated potentially dangerous levels of arsenic. 

“Our study provides compelling evidence that glacial rock flour has the potential to be both a source of fertility and toxicity to agricultural croplands,” explained Sarah Tingey, the lead author of the study. 

“It all depends on the bedrock beneath glaciers, which differs strongly from one region to the next. If the source rock contains high levels of toxic elements, such as arsenic, applying this glacial flour as a fertilizer could result in heavy metals being absorbed by plants and entering the food chain.”

Large-scale threat to human health?

The relevance of the study may extend far beyond the deliberate spreading of glacial flour onto fields, the authors warn. 

They highlight that 100 million people in South Asia have been exposed to arsenic through water from groundwater wells in what a World Health Organisation publication has called “the largest poisoning of a population in history”.

Glacier-derived sediment deposited across low-lying flood plains in the subcontinent may be the source of that arsenic.

Balancing benefits and risks

Previous work has exclusively focused on glaciers in Greenland whose bedrock is very different to that found at the study sites in Iceland and the Himalayas. 

“There is potential for using glacial flour as a source of nutrients to enhance the yields and nutritional value of crops, particularly as a measure to resolve micronutrient malnutrition in rural communities,” Sarah Tingey explained. 

“But we need to be careful not to accidentally expose smallholder subsistence farmers to potentially dangerous levels of toxic metals.”

 Large gaps in knowledge remain

While the new study provides strong evidence for arsenic accumulation within the narrow confines of its setting, its authors caution that further research is needed to resolve multiple unknowns related to glacial flour’s potential benefits and dangers.

Their research only involved glacial flour samples from two locations, one plant species, and one crop cycle grown under controlled indoor conditions. The potential long-term weathering effects of glacial flour could not be evaluated.

 “We urgently need to better understand the potential toxicity of soils within deglaciated landscapes and on glacial sediment floodplains,” the team writes, noting that Himalayan glaciers are the source of major Asian rivers that irrigate crops that feed up to 38 million people. “This is of particular importance for communities residing in the Punjab floodplain and the high Himalaya.” 

“Future research should include analysis of a wider range of lithologically contrasting flours, scrutiny of the biogeochemical mechanisms controlling nutrient release from mineral matrices, trials over single and multiple cropping cycles, and a consideration of both crop yield and trace element bioaccumulation impacts,” the study recommends.

“By leveraging the beneficial aspects of glacial flour application and mitigating potential risks, there is potential in harnessing glacial flour to sustainably bolster food security in the face of climate change,” the study concludes.

Sarah Tingey is a postdoctoral researcher on the iC3-affiliated METALLICA project, which is currently examining the release of heavy metals from glacier meltwater in the Arctic. She is based in Tromsø, Norway and can be contacted through her website or on Instagram.

The publication “The potential for glacial flour to impact soil fertility, crop yield and nutrition in mountain regions” is available open access in the journal iScience. The flour used for the study was collected from Sólheimajökull (Iceland) and Chhota Shigri (India). The study was conducted at the School of Geographical Sciences  of the University of Bristol and funded by the Cabot Institute.