Soil is full of amazing life with its own intrinsic value. Just like many other species, we humans benefit from it: Healthy soil not only provides food, feed, fiber and fuel, it also contributes to the stability of the whole Earth system. But living soils are at risk all around the world. So, in this episode, podcaster Anja Krieger and soil ecologist Matthias Rillig take a look into the sustainable future: How can we, as individuals and societies, nurture and restore the ecosystems of the soil? Get ready for the final episode of this series.

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TRANSCRIPT

Sound “Transversal Is A Loop” by Saša Spačal

Theme “Deep in the Soil” by Sunfish Moon Light

Matthias Rillig
You can only really conserve something if you feel its value. And if you understand what this is about.

Johannes Lehmann
We’re very often calling soil dirt. And dirt is really not soil, dirt is what you have on your clothes that you don’t want to have, soil is something different altogether. Soil is an ecosystem that sustains the Earth and humanity.

Yong-Guan Zhu
Wherever we live in this planet, we are connected by the microbial world. We should respect the microbial world, and we should harness the microbial world for our future!

Anja Krieger
Welcome to Life in the Soil, the podcast by the plant, fungal and soil ecology lab at Freie Universität Berlin.

Richard Bardgett
To me, a basic principle should be that soil is seen as a common good, and that we have a responsibility to maintain or even build the fertility of that soil for the next generation.

Katie Field
If you can sort of breed back this ability to make the best use of existing helpers in the soil, then there’s real gains to be made. And it could be that actually soil fungi helps us mitigate some of the effects of climate change.

Yong-Guan Zhu
Soil is the habitat with the richest microbial diversity on the Earth. So we should not under-appreciate the biodiversity under our feet.

Vocoder sings Life in the Soil

Yong-Guan Zhu
These communities, they can help heal these problems we are facing in modern days.

Anja
Hello friends of the soil, this is your host, Anja Krieger. Soil is full of amazing life with its own intrinsic value. Just like many other species, we humans benefit from it: Healthy soil not only provides food, feed, fiber and fuel, it also contributes to the stability of the whole Earth system. But living soils are at risk all around the world, as we discussed in the last episode. So, this time, we’re going to look into a sustainable future: How can we, as individuals and societies, nurture and restore the ecosystems of the soil? Get ready for the final episode of our mini-series on soil ecology!

Music – Building the Sledge by Blue Dot Sessions

Anja
Humans have always had a close relationship with the soil. Long ago, when people settled down and learned to grow and breed crops and animals, they started to shape landscapes and ecosystems. But in the middle of the last century, the rate of change accelerated. From the human perspective, it seemed like a big success story.

Katie Field
Since the 1950s, 1960s, when there was this agricultural Green Revolution, we call it, which is when there were huge leaps forward made in crop breeding in terms of increasing yield and reducing wastage and improving the efficiency of the food crops that we use today.
There were also huge leaps forward in technologies made. So things like producing fertilizers that would help your crops grow, pesticides, so that your crops weren’t eaten, and fungicides and things like that, that just overall improved the efficiency and effectiveness of agriculture in the way that we’re familiar with today.

Anja
That’s Katie Field. Katie is a professor of plant-soil processes at the University of Sheffield in the UK. You might remember her from our second episode, where she told us about the fascinating, age-old relationship between plants and mycorrhizal fungi.

Katie Field
What the breeders were inadvertently doing is actually selecting for traits in crops that aren’t conducive to forming mycorrhizal associations, or certainly not effective mycorrhizal associations. So, if you imagine you’re choosing a crop that’s going to be very responsive to a nitrogen-based fertilizer application or phosphorus-based fertilizers – it’s going to do well when it has a pesticide added to it, also fungicide in a similar way – actually, what you’re doing is you’re selecting a plant that doesn’t like to form an association with a fungus that’s going to help it get more nutrients in return for carbon because it doesn’t need to – because it’s in the soil next to it.

Anja
As we discussed in episode 2, most plants form relationships with mycorrhizal fungi, to trade. The plant provides the carbon, and the fungus feeds the plants with nutrients to grow. But if you are a plant that gets pampered by a lot of nutrients from your human farmer, you won’t need the fungus anymore.

Katie Field
And so, actually, by doing this, introducing these, what seems to be desirable traits in modern crops, is actually inadvertently selecting for plants that don’t form effective mycorrhizas. And that’s a real problem when we’re looking at issues facing agriculture today, in terms of sustainability.

Anja
So the development of industrial agriculture led to a situation where beneficial fungi can’t help plants thrive anymore. Instead, farmers offered their plants artificial, chemical inputs, like pesticides and fertilizers. But these new plant partners had to be constantly added to the soil. And they came with a lot of downsides.

Katie Field
So we know that fertilizer production and application has catastrophic impacts in terms of climate change. The manufacturing processes and the application processes, for instance, make up a horrifying amount of global CO2 emissions. They’re also really expensive. So farmers in poorer regions of the world potentially cannot get access to as much fertilizer as perhaps someone in a richer portion of the world has. And also, they’re damaging to the environment.

Music – Valantis by Blue Dot Sessions

Anja
In recent years, awareness of these issues has been growing. And around the world, farmers have started to rethink the way they treat their fields. They are reviving their soils, reducing chemical inputs, and discovering that this saves a lot of money. Feed the soil to feed the plants is the new mantra.

Katie Field
So I think in the future, if we were able to successfully harness fungal helpers in the soil to help us reduce our reliance on agricultural inputs, then we’d be looking at developing crops that form highly effective symbiosis with these fungi.

Music – Tidal Foam by Blue Dot Sessions

Marcel van der Heijden
By stimulating soil life we expect that the losses of nutrients by leaching can be reduced. So if there are a lot of mycorrhizal fungi in the soil, they can prevent that nutrients such as nitrogen are leaking out – but stay in the system. So that’s what we want to do.

Anja
Just like Marcel van der Heijden, many soil ecologists are looking for ways to restore the natural powers of the soil. Bala Chaudhary from DePaul University* in Chicago is an expert on fungi – you might remember her from episode 2.

*Correction (April 6, 2021): The audio version incorrectly states that Bala Chaudhary works at the University of Chicago. She’s an Assistant Professor at the Department of Environmental Science and Studies at DePaul University.

Bala Chaudhary
Oftentimes, the best thing to promote AM fungi in your soil is…first, to feed them. And so make sure you have lots of healthy plant hosts, native hosts that are there that can provide a carbon source for the fungi and then just don’t disturb them – so avoid soil disturbance and tillage.

Music – Alum Drum Solo by Blue Dot Sessions

­­­Anja
Tillage – yes, this iconic practice! You might have learned about the plow as one of the first tools in human agriculture. For a very long time, humans prepared the land this way. Oxen, horses and later the tractor dragged plows across the field to open and turn the top soil. Tilling has many benefits. It stops unwanted weeds from growing, mixes plant residues, seeds and manure, loosens the soil, increases water infiltration, and prepares the seedbed. But plowing and tilling also have huge side-effects, as we discussed in our first episode on the soil habitat. They destroy the intricate architecture of the soil, this complicated 3D structure of solids, pore spaces and tiny tunnels. That has led to the degradation and compaction of soils around the world, to erosion by wind and rain, and the loss of carbon to the atmosphere. This threatens many of the organisms in the soil. But there’s another way.

Marcel van der Heijden
The idea is to cover the land as much as possible. And this is usually very good for soil biodiversity. It increases the abundance of mycorrhizal fungi, it increases earthworms, so all beneficial soil organisms and it also can enhance the amount of carbon which is stored in the soil which would be good for climate change.

Anja
Marcel van der Heijden and his colleagues at Agroscope in Switzerland are conducting research on sustainable farming. They investigate the amounts of crop that can be produced through alternative practices such as organic or conservation agriculture. After the main crops have been harvested, cover crops can be planted. This supplies the soil with nutrients, stability, and protection from weeds and erosion in the off-season. In addition, more and more farmers are growing a larger variety of plants and crops.

Marcel van der Heijden
If farmers do more crop diversification, that means, for instance, crop rotation, growing different crops after each other or even mixing crops in the same field – this together with an increased cover, so longer time the soils are covered with crops, that’s very beneficial for agriculture, it has a positive influence on soil quality and sometimes also on soil carbon accumulation.

Anja
Marcel says it cannot be on farmers alone to make these changes. Governments need to make guidelines and rules to support farmers, and customers need to be willing to pay for food that’s produced sustainably. A tax on fertilizer and pesticide use could make chemical inputs more expensive so that farmers would only apply them if really needed. Organic farming and conservation agriculture are promising pathways – if they allow to feed enough people, Marcel says.

Marcel van der Heijden
I really like organic farming because a range of studies have shown that usually, it has a positive impact on biodiversity and on a range of environmental services. However, there’s also one weakness of organic farming and that is that the yields, and the yield stability is usually lower. That means the yield, the amount of food produced per hectare of land, is often 20 to 25% lower. So, I think it’s very important for organic farming to find ways to reduce this yield gap with conventional farming.

Music – Ether Ridge by Blue Dot Sessions

Maddy Thakur
Imagine a very warm day, and you have large trees. The microhabitats of those large trees would be the shadows that trees create for a lot of herbivores, which can come down and sit under those larger trees. If you remove those larger trees, you lose microhabitats, then you don’t have places for those herbivores. Now let’s think about soil organisms. A lot of soil organisms live in microhabitat. For example, earthworms create a lot of microhabitats where collembolans, fungi, oribatid mites, isopods, a lot of those organisms live on those tunnels made by earthworms. If you lose those earthworms, you lose those micro-habitats.

Anja
What happens when climate change brings stronger heat waves and droughts? Maddy Thakur told us about the impacts of climate extremes on soil organisms in the previous episode. One way to tackle this might be the practice of rewilding. The idea is to re-establish wild areas in nature, and protect the animals that shape the ecosystem. Like earthworms, which build pathways and shelters for other organisms – tiny microhabitats.

Maddy Thakur
And imagine, when you have those climate extremes, those organisms would really like to live in those microhabitats, because those microhabitats are cooler. Those microhabi-… ehm, cooler in terms of temperature. Well, they’re also cool, but also cooler (laughs) in terms of surrounding temperature. So there, they would go and find refuge, find the shelter. So rewilding has many such advantages of rescuing animals during a very, very warm day or a very, very dry day. So if you loose those organisms, which create those microhabitats – we call these organisms ecosystem engineers. So rewilding has to consider ecosystem engineers of various sizes.

Music – Ether Ridge by Blue Dot Sessions

Anja
Attention has focused mostly on the bigger engineers of ecosystems, like bison for example. The ingenuity of the smaller ones was often overlooked. If rewilding was also applied to the tiny life in the soil, this could have big impacts. If you protect the earthworm in places where it naturally lives, you’ll also protect many other organisms. Native earthworms digest organic matter and excrete it as a fertile material, so called wormcast. This way, they increase the overall health of the soil. Yong-Guan Zhu, a member of the Chinese Academy of Sciences, first learned about them as a child.

Yong-Guan Zhu
I grew up on a farm. So I play with soil, play with soil animals, particularly earthworm. So, earthworm usually was used as a animal feed for like, ducks or other animals. When I was a child, we learned to collect earthworms from the field and feed the ducks at home.

Anja
From the farm, Yong-Guan moved to the city to study biogeochemistry and environmental science. Like him, millions of people around the world have left the countryside.

Yong-Guan Zhu
Urbanization is one of the major drivers of environmental changes and also ecosystem changes. With the urbanization, the cycling of the material is to some extent broken, because many of the materials we excrete cannot be put back into the ecosystem where we get our food from. So, the soil ecosystem is not well-balanced in terms of nutrient input and the input of organic materials.

Anja
Every day, huge amounts of grain, vegetables, fruit, and meat from farms outside of town are delivered to hungry people in the cities. This way, the soils in the countryside are stripped of nutrients like phosphorus, and organic matter.

Yong-Guan Zhu
So, the problem is that for the urban population, we have to grow more food from the field. And to grow more food we have to use chemical fertilizers, like nitrogen fertilizers, phosphorus fertilizers. So, when we consume the food, we also bring these nutrients and concentrate these nutrients in the urban ecosystem – the wastewater treatment plants, the landfills. So, these nutrients end up in those areas. Ideally, they should go back to the field where we need the nitrogen and phosphorus to sustainably produce food.

Anja
So basically, we need a good system to recycle the nutrients between the cities and the farms.

Yong-Guan Zhu
To make the urbanization process sustainable, we must reconnect the urban ecosystem with the natural ecosystem. So, let the material move throughout this system in a closed loop, so that we don’t have the accumulation in one side and on the other side that we have to import nutrients from far away or from the atmosphere by chemical synthesis. So this is the problem we need to solve.

Anja
There’s a challenge: The organic waste from our cities’ wastewater treatment plants doesn’t only contain nutrients. It also contains pollutants and other chemicals, like the remnants of the drugs we are taking, and pathogens that could be resistant to antibiotics.

Yong-Guan Zhu
So, on one hand, we should try to recycle the urban waste material. But on the other hand, we have to make sure that this recycling is safe.

Anja
One way to do this, Yong-Guan told me, is to separate the nutrient cycle from the microbial cycle. In other words: Return the phosphorus and nitrogen to the fields, but without the bugs in it.

Yong-Guan Zhu
One major technology we have been developing is to turn sewage sludge into biochar by pyrolysis. So, it’s a technology that we heat the sewage sludge at a high temperature, say 500 or 600 degree with minimal oxygen supply. So, the organic material can be converted into more or less carbon. And this material still contains phosphorus and partly also nitrogen. And this material is quite porous and also very beneficial to the soil structure – so the indigenous beneficial microbial community can grow better in the soil without the invasion of those bacterias that might contain a lot of resistant genes.

Music – Stock Still by Blue Dot Sessions

Anja
This idea was inspired by a discovery from Brazil. In the Amazon, archaeologists found black and very fertile soils, full of biochar which is a type of charcoal. These soils turned out to be hundreds to thousands of years old.

Johannes Lehmann
Terra preta de índio, the black soils of the Indians, Amerindian populations from before the arrival of the Europeans and South America, have modified their environment to an extent, and specifically the soils, that we still today have large pockets of very fertile, very carbon rich soils throughout the Amazon basin.

Anja
Johannes Lehmann from Cornell University is fascinated by these ancient soils. Biochar can be produced from biomass such as leaves, crop residues, nutshells or animal manure. Heated under the exclusion of oxygen, it turns into an entirely new material that can last for long periods of time.

Johannes Lehmann
It’s a very exciting story of discovery and history. The collaboration between different scientific disciplines, archeology, geography, anthropology, and soil science and geology.

Anja
To explore these special soils, Johannes and his colleagues have travelled the Amazon region.

Johannes Lehmann
You can step out of your car almost anywhere in the central Amazon and ask somebody, a farmer, do you know any Terra Preta around here? And he says, or she says, yes, yes, just go a few kilometer over there, there’s a farmer who has a piece of land! And we visited many farmers. One farmer, I remember vividly, she told us, she explicitly was seeking out this piece of land because it had terra preta. And she said she always wanted to come here. Now she’s so happy she’s here. And since she moved there, she has fewer illnesses, she is happier, she can feed her children, not only because she feels that she’s producing more food, but also more nutritious food. And that makes perfect sense because these soils not only have a greater production capacity, but they’re also full of nutrients that we then also find in the crops that are grown on this land. Farmers know about it, the population, the rural population knows about this in this area. And for certain, the national research institutions in this region all know about it.

Anja
Were the ancient creators of these soils aware of what they were doing? There are good reasons to assume that they modified the soil on purpose, Johannes says. And in any case, the discovery of Terra Preta has important implications for the way we treat soils today.

Johannes Lehmann
Those soils are remarkable, not only because they are fertile, and they store a lot of carbon, but also because they tell us something about the interactions of humans with their environment and how they were able to modify their surroundings, to sustain what we now appreciate as being a very complex and sophisticated society. And that’s really exciting and should teach us a very important lesson of how humans can survive and thrive in a very challenging environment such as the central Amazon by smart soil management.

Music – Algae Trio by Blue Dot Sessions

Anja
As you can see, there’s no shortage of ideas to save the soils, from farming to rewilding to waste management to growing more trees and protecting the biodiversity aboveground.
But what can you do if you don’t run a farm, a forest or a wastewater treatment plant? Actually, a lot! Here are some simple steps I learned from the Global Soil Biodiversity Atlas.

Narrator (Kevin Caners)
· Look out for the organic products in your supermarket
· Consider leaving some branches and plant waste in your garden to compost naturally
· Try to reduce your rubbish, and recycle whenever possible
· Be sure to take any leftover prescription medications back to the pharmacy – and to never flush them down the toilet
· Look for ways to reduce your carbon footprint – consider switching to a green energy provider at home, and whenever possibly, use a bicycle or public transportation to get around
· Encourage your local authorities to take soil protection seriously, and let them know if you notice any problem areas

Anja
And there’s more. Don’t throw plastic in the biowaste, for example – so it doesn’t end up on the field. As individuals, we can be the movement on the grassroots level. But it will also be on politicians to act – and on citizens to demand soil protection. For Richard Bardgett from the University of Manchester, political action is really urgent.

Richard Bardgett
I think environmental policy absolutely has to act now, there is little time to ponder on this –
because ­­­­something like 30% of all soils on the Earth are degraded, and those trends are continuing. So we have a commitment – or need a commitment – to prevent further degradation and to restore those degraded soils. So that needs to be acted upon now, because the implications of that soil degradation for people are massive! They’re important in terms of food security, and also in terms of things like climate mitigation. I think one thing that could help here is if soil is seen as a common good. And this requires policies and support mechanisms at both a local and a national level to ensure that farmers and land users can actually invest in soil care, in order to ensure that the soil is left healthy, or even increased its fertility for future generations.

Music – Lahaina by Blue Dot Sessions

Matthias
Soil is not just this inert substrate in which you grow plants, so they don’t fall over! (Laughs) It’s a world on its own, it’s full of life, full of biodiversity, full of interactions, and it gives rise to some key processes and services for ecosystems, and also in the end for us humans. So I think the most important thing that we can achieve, or the most important message we can send is, you know, how fascinating soil really is. Because it’s not obvious at first sight, right, because you cannot see very much and most of it is hidden from our experience and our senses.

Anja
That’s Matthias Rillig, the soil ecologist who invited me into this adventure of a soil podcast.

Matthias
I think once that message is out­­­­ and more commonly accepted by people, (who) start caring about the soil – and I think this realization really has been happening in the last few years more and more – is my sense of it – both in the science world and also in society, I think there is a growing appreciation for the importance and significance of soil. So once this word is out, I think that it will be easier to implement changes that will benefit our soils. And there’s a number of things you can do. I mean, you can conserve the soils that are there by you know, setting aside areas or by stopping basically damaging management practices, for example, on agricultural soils or in other situations, in the city. Urban soils, for example. So you can try to remove negative impacts and conserve the soils that have not been affected yet, you know.

Sometimes that may be strange things that you would have to do. I just talked to a colleague of mine, Dirk Schulze-Makuch who works in the Atacama Desert, and he says…these soil are some of the driest soils on Earth. And there’s a specific microbial community that deals with these extreme drought. And for some reason, because of climate change, there is an increase in precipitation in this area. And so we’re… yeah, climate change is sort of threatening these communities, strangely enough, that are adapted to this extreme drought. And so how can we conserve them? How can we conserve soil – it’s not so easy, right? I mean, I think it requires a lot of thought. So conservation is one thing. But you can only really conserve something if you feel its value, and if you understand what this is about. So, that’s why I’m saying that the first step has to be creating this understanding. And then you can also conserve it once you better understand it. But what you can also do, you can also restore areas that have been damaged by, you know, pollution, by agriculture by, you know, being exposed to urban pressures. You can try to bring these soils and ecosystem back on a trajectory towards recovery. And, you know, restoration ecology is its own field. And many factors are important, what are the plants you use, what are the management interventions that you install, but in the end, it is definitely about also restoring the soil and its biodiversity. And I think that will, that’ll take some creative approaches to make progress.

Anja
Great, thank you so much for taking me on this journey through the soil – I had little clue about this environment and world before I met you, so I’m really thankful. And I hope our listeners also learned some interesting insights and maybe are now interested in learning more. So there’s a lot of stuff out there, literature and documentaries and all kinds of things that you can watch or read, to find out more about life in the soil.

Matthias
…and if you want to hear more, you can get in touch with us!

Theme Music

Anja
This was episode 6 of Life in the Soil with Katie Field, Marcel van der Heijden, Bala Chaudhary, Maddy Thakur, Yong-Guan Zhu and Richard Bardgett. Matthias and I would not have been able to make this podcast without our fabulous story consultants. So, for the credits, I’m handing over to them.

Moisés Sosa Hernández
Hi there! I am Moisés Sosa Hernández, and I try to unearth fungi that are hiding deep in the soil. On behalf of the whole lab, I’d like to thank our stellar cast of guest experts for sharing their knowledge with us!

Stefanie Maaß
My name is Stefanie Maaß and I study the cutest and fiercest of all soil animals – springtails and mites! My thanks goes to Sunfish Moon Light for composing the wonderful theme song.

Stefan Hempel
I’m Stefan Hempel and I focus on soil fungi, their communities and their interactions with plants. I’d like to thank the amazing crew at Blue Dot sessions for their beautiful music.

Eva Leifheit
And my name is Eva Leifheit. I work on mycorrhizal fungi, their role in soil carbon cycling and interactions with global change factors. Huge thanks to the BiodivERsA network for generously funding our podcast series!

Anja
…and we thank Kevin Caners, Maren von Stockhausen and Saša Spačal. Our team also includes Tessa Camenzind, Milos Bielcik, Joana Bergmann and Gaowen Yang. Just visit Rilliglab.org to contact us. That’s r-i-l-l-i-g-l-a-b-dot-org.

Vocoder sings Life in the Soil

This was our final episode, but do stay subscribed to our feed, just in case. Last but not least, thank you for caring about the life in the soil! Let’s keep celebrating it.

—End of audio—

FULL CREDITS
Produced by: Anja Krieger and the Rillig Lab
Funded by: Digging Deeper / BiodivERsA 
Guest experts: Katie Field, Marcel van der Heijden, Bala Chaudhary, Maddy Thakur, Yong-Guan Zhu and Richard Bardgett
Cameo voice: Kevin Caners, host of Elephant Podcast
Story consultants: Eva Leifheit, Stefan Hempel
Cover art: Maren von Stockhausen 
Theme song: Sunfish Moon Light / Future Ecologies 
Music: Blue Dot Sessions 
Sounds: Intro: Saša Spačal, “Transversal Is A Loop”

The Digging Deeper project was funded through the 2015-2016 BiodivERsA COFUND call for research proposals, with the national funders Swiss National Science Foundation, Deutsche Forschungsgemeinschaft, Swedish Research Council Formas, Ministerio de Economía y Competitividad and Agence Nationale de la Recherche.