“Such a soil moisture field laboratory as the one here in Potsdam has no equal anywhere in the world.” — Interview with Prof. Sascha Oswald

In the DFG (German Research Council) research group entitled “Cosmic Sense”, Prof. Sascha Oswald is working on methods to determine soil moisture based on neutron density. This forms the basis for all agriculture and forestry and plays an important role in climate research. In this conversation, we talk about the desire to set new impulses in environmental protection.

Prof. Oswald, you actually have a doctorate in physics and as a professor at the Institute of Environmental Sciences and Geography at the University of Potsdam, you work with topics such as soil moisture, groundwater protection and microplastics. So how was it that you made the switch from physicist to geographer?

Actually, the orientation towards environment aspects had already been established in my diploma thesis. At that time I was already working on an environmental ressource, namely groundwater. During my doctorate, which I had started in Heidelberg, my supervisor had received an offer from the Swiss Federal Institute of Technology in Zürich (ETH). We had mutually come to an agreement: If he decided to go, I would go with him. We then moved to a department of environmental sciences there and I completed my doctorate. It was about the density and flow of groundwater, i.e. environmental issues. That’s how it started with the environmental sciences, which I continued to work on and research over the next few years until I was offered the professorial position at the University of Potsdam in 2009.

What fascinates you so much about water?

For me, it’s more about environmental protection on the whole. I was motivated by the fact that: Water is an important resource that is also utilised heavily. This interplay between science and application, how to protect the environment instead of exploiting it over and over again, is what intrigued me. We all rely on water. Both, here and in other countries. Over the years, however, my field of interest has expanded and now includes soils. Soils are often a rather marginal topic in the public eye. Despite the fact that what we depend on in order to survive, i.e. our food, grows in it. It is therefore essential to take care of this resource.

The topic of soil moisture sounds very specific at first glance and sounds like a somewhat niche topic. To what extent is the topic relevant for our understanding of the planet or in terms of climate research?

First of all, soil moisture, i.e. the water stored in the soil, is at the interface between the atmosphere and the earth’s surface. There is a lot of interaction going on there: On the one hand precipitation, and on the other evaporation via vegetation into the atmosphere. Soil moisture therefore contains, firstly, a pool of water for natural vegetation. This water is the very foundation of sustaining nature. It is equally important for agriculture and forestry. Recent years have highlighted the challenges we will come up against if there is not enough water available. Secondly: Soil moisture is important for the atmosphere and has an influence on weather patterns. It will help determine how the climate develops. Thirdly: The issue also includes seepage from the soil water reservoir, i.e. how much new groundwater is formed. That in itself is a question of equilibrium: Is there a surplus, or is there too little? If the whole thing changes, that will affect groundwater recharge.

In order to measure soil moisture, you have to take into account radiation from space, particle showers and neutrons in your research. How did you come up with this idea?

The first time I came into contact with technology was in 2002 at the Swiss Federal Institute of Technology in Zürich (ETH Zurich). A professor of soil physics gave me the impetus to take images of soil water with neutrons in the laboratory. The technique was still relatively new at the time. Then in 2008, an article was published by a team in the USA. They had used natural neutrons to detect soil water outdoors. That was quite exciting, because it showed that this was a new approach that could work. Here at the University of Potsdam, I then used some of the professional funds to build that up. In Europe, we were among the first to work with it and publish on it.

How does this method work?

Neutrons are particles that occur everywhere on the land surface in small quantities due to atmospheric particle showers. Water has an important property: It slows down neutrons, can divert them or capture them. With our instruments, we detect the neutrons of a certain energy range. Based on the number of neutrons, we can then determine how much water is present in the soil in the entire environment.

What are the advantages of determining soil moisture based on neutron density?

The other measurements are actually point measurements. We have different measuring principles. However, they are usually probes that are installed in one place in order to determine the soil moisture locally. The fact remains, of course, that the value is highly variable. You can see that clearly in a field: There are different textures and the vegetation is different. And there is a lot of movement due to plant roots or organisms. Soil moisture is therefore very heterogeneous and generally varies between a few percent and about 50 percent. This means that individual measurements are not of much value. You don’t know then just how representative it is.

You can, however, bury hundreds of probes, then you get a spatial impression and a better average. That puts us at a scale of about 100 metres. And the Cosmic Ray Neutron Sensing (CRNS) method is an order of magnitude above that. It averages over a radius of 150 to 200 metres. That’s about ten hectares over which you get an average soil moisture. There are only a few other methods that can cover such a scale, and they do not cover the same depth range. But we also integrate these different approaches and get the best out of the combination.

Do you have a goal that you would like to achieve in the next 5 to 10 years?

We are trying to expand. In the research group, we deployed a cluster of 20 CRNS probes, which then covered an area. This allowed us to cover a square kilometre for the first time. What we have achieved here in Potsdam in this regard is unparalleled worldwide. Now our goal is to record even larger catchment areas. That’s not possible at the moment because you don’t simply have 1,000 probes on hand. We would like to find solutions to cover a larger scale in the future. My wish would be to establish this kind of soil moisture measurement regionally and nationally and to obtain a more accurate picture of soil moisture. That would be a big step towards developing more accurate weather models, for example.

You wrote your diploma thesis in Heidelberg and completed your doctorate in Zurich. You worked for a company in Baden in Aargau, at the University of Sheffield and at the Helmholtz Centre for Environmental Research in Leipzig. Since 2009 you have been at the University of Potsdam in Potsdam-Golm. What do you think is special about the Potsdam Science Park?

The Potsdam Science Park is really special because the university’s natural sciences are all bundled here. There is a lot of development and activity over here. New buildings are being built, the area is expanding. We have the institutes of physics, chemistry and biology right on our doorstep, we are very close together, can exchange ideas and learn from each other. Potsdam is also ideally located and well connected. The entire capital region with Potsdam and Berlin is very lively, very active, there is a lot of research and a lot of conferences. And we benefit from the proximity to the non-university research institutions.

Which institutions do you work particularly closely with?

As an institute, we have very diverse collaborations with different institutes here. For example, there is the German Research Centre for Geosciences (GFZ), the Potsdam Institute for Climate Impact Research (PIK) and the Alfred Wegener Institute (AWI). I also work a lot with the Helmholtz Centre for Environmental Research in Leipzig, where I used to work. We have a close working relationship with them. It’s not on our doorstep, but it’s very close from a technical point of view, because they’re also researching the CRNS method there. We also work more specifically with the Leibnitz Institute for Agricultural Engineering and Bioeconomy (ATB). We have a test site in Potsdam-Marquardt where we have set up a cluster of several probes, a small science park for CRNS research, so to speak, where people from Berlin are also involved.

What do you wish for the Potsdam Science Park in the next few years?

For my working group, I have been wishing for more laboratory facilities for a long time. At the moment, however, there is a new building that we will move into. Overall, a lot is happening, which is reassuring. Space is still scarce, despite the new buildings, because the demand is so high. The availability of living space for students and staff is getting smaller by the day. That’s because the location is so appealing. But I also see that a lot is being done and I am curious to see what will happen here in the next few years.

Prof. Oswald, thank you for the interview.

This blog and the projects of Standortmanagement Golm GmbH in the Potsdam Science Park are funded by the European Regional Development Fund (ERDF) and the State of Brandenburg.

Photo: Cosmic Ray Neutron Sensoren (CRNS) © Prof. Sascha Oswald