Several studies have gradually established that the properties of glacial rock flour from Greenland make it especially useful in enhancing the fertility of agricultural soil in Africa. However, a new study shows that adding glacial rock flour does not improve the ability of soil to retain water, and another explanation is therefore needed.
Over millennia, the Greenland Ice Sheet has abraded the bedrock, creating a fine-grained sediment known as glacial rock flour.
This has many useful properties, such as removing CO2 from the atmosphere and being eminently suitable for mixing into soil, thereby improving the quality of agricultural soil.
Rock flour washed out from under glaciers also explains why the Northern Hemisphere has some of the world’s best agricultural land.
This land was formed during the last ice age, when glaciers eroded the underlying bedrock and deposited large quantities of glacial rock flour in the soil in Europe and North America, which still benefits agriculture today.
Researchers have long known that the minerals in the crushed rocks make glacial rock flour suitable for enhancing the quality of agricultural soil, but the researchers thought that the rock flour also improves the ability of soil to retain water and thereby improves the conditions for plant growth.
However, a new study refutes this theory. Although glacial rock flour appears to improve plants’ ability to withstand drought in fields in Africa, this is not because glacial rock flour improves the ability of soil to retain water.
“This is not unduly surprising, but it is still very useful because it forces us to reconsider and to find other explanations for why glacial rock flour enables plants to cope better when they lack water,” explains a researcher involved in the research, Minik Rosing, Professor, Globe Institute, University of Copenhagen, Denmark.
The research has been published in the European Journal of Soil Science.
Increasing crop yields by up to 50%
Glacial rock flour is present throughout Greenland, and researchers have recently become aware that this may be an easily accessible and abundant resource that can help to mitigate both climate challenges and food scarcity in Africa.
Research by Minik Rosing’s research group has shown that glacial rock flour can increase crop yields by up to 50% in Ghana and by up to 30% in Denmark. In addition, one tonne of glacial rock flour spread on a field can absorb 250 kg of CO2.
In the new study, the researchers aimed to improve understanding of how glacial rock flour benefits plant growth and its role in plants’ ability to tolerate drought.
“We performed many experiments with glacial rock flour to learn more about its properties and potential, but here we specifically examined how it affects soil water retention,” says Minik Rosing.
No effect
In Ghana, the researchers investigated whether soil in pots retained water better if glacial rock flour was mixed into the soil. This could explain how plants growing in a mixture of glacial rock flour and soil perform better during extreme drought than plants growing in soil alone.
However, mixing soil with glacial rock flour only marginally improved water retention. There must be another explanation for the improved plant growth.
“We observed a small effect, but it was not large enough to explain the difference,” notes Minik Rosing.
Another possible explanation?
Minik Rosing has another potential explanation for how plants thrive better in soil with glacial rock flour.
Perhaps the plants tolerate drought better when the soil has more nutrients and they thus can use less energy and less of the scarce water to extract the nutrients.
Previous studies from Minik Rosing’s research group have shown that using glacial rock flour improves plant growth more than irrigation does.
However, using both glacial rock flour and irrigation achieved the best results.
“We conclude that glacial rock flour improves the ability of plants to tolerate drought, but we cannot yet explain how and future studies will need to do this. My own guess is that this results from the plants having to use less energy to absorb nutrients, and we will find out whether this theory can be substantiated in new studies,” explains Minik Rosing.
“Limited short-term benefits of glacial rock flour for enhancing the physical quality of tropical arable soils” has been published in the European Journal of Soil Science. The Novo Nordisk Foundation supported the research.
