5 January 2017

New PhD-project aims to determine plant nutritional value of glacial rock flour


New PhD student Klara Cecilia Gunnarsen will be working with professor Andreas de Neergaard to determine the plant nutritional value of glacial rock flour from Greenland. Klara will be focusing on how plants respond to glacial rock flour application and how weathering of rock flour increases soil fertility.

The Greenland Perspective project "Glacial Rock Flour" investigates whether the massive amounts of fine mud deposited in many Greenlandic fjords and lakes can be used to replenish depleted soils. The ultimate goal is to improve the fertility of tropical soils and to create jobs and growth in Greenland.

Klara Cecilia Gunnarsen

Klara Cecilia Gunnarsen. Photo: Private

Before the project team can really begin to think about the mud as a resource for agricultural purposes, questions concerning the plant nutritional value of glacial rock flour are to be answered: Can weathered minerals from rock flour serve as nutrient sources for plants? How does soil type and plant species affect the plant response? Are all rock flour materials of equal value as a soil improving amendments?

Many questions remain 

In the coming years PhD student Klara Cecilia Gunnarsen at the Department of Plant and Environmental Sciences will be working on answering these questions. Prime focus of the PhD will be to investigate the interaction between plant and soil and the processes by which nutrients become available after rock flour application.

“Nothing is really certain regarding the plant response to glacial rock flour yet,” says Klara. “Some of the first experiments showed a higher uptake of phosphorus, magnesium and potassium, but how it is actually linked to glacial rock flour, is still unclear.”


“Some of the first experiments showed a higher uptake of phosphorus, magnesium and potassium, but how it is actually linked to glacial rock flour, is still unclear.”

Klara Cecilia Gunnarsen

Klara explains that there might be a great difference between the types of rock flour. The materials can have different properties, depending on which geographical areas they are taken from and how they have been deposited. There is a general distinction between sediments from the seabed and from freshwater lakes, but even within these distinctions the variation may affect how plants respond to the individual type of rock flour. The types of minerals and presence and availability of plant nutrients may vary from material to material. A handful of these materials have been characterized, but many still remain. Mineral characterization is important in order to understand the plant response to rock flour application.

Klara’s project aims to tackle some of these questions. Through pot experiments she wishes to examine the general plant response. She will start off by asking which nutrients become available for plants when soil is amended with rock flour. Klara also means to screen different types of materials and thereby map out, which types of rock flour amendments are able to give higher plant yields. In cooperation with Greenland Perspective’s Brazilian partners at ESALQ, University of Sao Paolo, Klara aims to make field scale experiments on depleted tropical soils part of her project.

Soil is not just soil 

This PhD project examines the plant nutritional value of glacial rock flour.

“The soil isn’t ‘just soil’", Klara explains. It contains water, plant roots, dead organic matter, bacteria, fungi and much more, making soil a complex material to work with. The biological, physical and chemical properties of a soil are determining for how nutrients are available to plants. The soils in Brazil are very different from the soils in Denmark, which may affect the plant response to rock flour application.

So far, rock flour has only been tested in depleted Danish soils and it will be interesting to see if rock flour amendments in other soils will give similar positive plant responses.

Klara’s PhD project will also contain an examination of the exchange of ions between rock flour and soil solution and between soil and plants. She is interested in understanding the mechanisms involved in enhanced nutrient uptake in plants by raising questions such as how ions released from rock flour interact with soil and whether plants use certain strategies to acquire nutrients provided through rock flour amendments.

Plant roots can excrete simple and complex molecules that can enhance solubilization of minerals. She will look into how root exudates can enhance weathering of rock flour. She aims to understand whether plant nutrients in soil can be linked directly back to the rock flour materials or if nutrients become available to plants due to other shifts in the soil solution equilibrium after rock flour application.

The goal is to investigate the questions in part by using a technique called DGT (diffusive gradient in thin films). The principle of this method relies on thin gels that are able to extract nutrients from the soil in a manner similar to plants. Klara has experience with this type of experiment from earlier work done in collaboration with BOKU, University of Natural Resources and Life Sciences, Vienna.  

Glacial rock dust

Glacial rock dust.

“It would be exciting to work with DGTs and build on my collaboration with BOKU again. They hold much experience and have contributed to develop the DGT method and advance the analytical methods for it,” she says.

Klara’s PhD is supervised by professors Andreas de Neergaard, Beatriz Gomez-Munoz and Lars Stoumann Jensen.