“Do you hear the earthworms coughing as they move through the dark earth”, it says in a nursery rhyme. In fact, in the absence of a lung, earthworms cannot cough. But how they slide through the floor can be heard. At least if you listen carefully. The art and science project “Sounding Soil” (in English: sounding earth) uses special microphones to make life underground audible. And shows that there is a lot going on there.
“In a handful of earth there are more living things than people in the world,” says Marilena Schumann from Sounding Soil, where various scientific institutions and the Zurich University of the Arts work together. Their microphones record frequencies close to the human auditory spectrum. Such frequencies are mainly caused by insects and earthworms.
In addition, a large number of plants, fungi and microorganisms such as bacteria live in the soil, which you cannot hear even with the microphone. The project researchers also do not record larger animals such as moles or mice; Schumann suspects that they would overdrive the devices. But one thing is certain: all living things together produce the layer of earth from which our food grows. A lot of exercise therefore speaks for a fertile soil.
Sometimes you can also see something of life underground above ground. But the diversity remains hidden.
(Photo: Frank Gaertner – www.facebook.co/imago images / YAY Images)
In order to convey a feeling for this diversity, Sounding Soil presents flower meadows, forest floors, compost and fields in public places. Every floor has its own sound. It cracks, crackles, scratches and squeaks. The scientists cannot assign all the noises, but they have already identified the originators of the squeaking: they are ants.
With their project, the researchers and artists also want to draw attention to the problems of soil. “The soil is our livelihood,” says Schumann. “But the way we treat it at the moment, it won’t last forever.” In addition to the sealing by the development, the compaction of the soil is a particular problem: “It’s just way too narrow,” says Schumann.
Compaction destroys soil as a resource
According to an international study from 2017, 68 million hectares of land around the world are affected by compaction. The reason is the use of large machines in agriculture. Roll them over the fields, compressing the ground into deeper layers. As a result, the water no longer seeps away properly, but instead flows away above ground – and in the process washes the top of the arable land, the top, fertile layer of the soil. When plowing, the soil is loosened, but this only affects the top layer. The subsoil is even more compacted.
The process also has an impact on life in the soil. Earthworms and other inhabitants of the earth feed primarily on the “litter”, of freshly dead organic material that normally remains on the surface. “If we incorporate this mechanically, the earthworms won’t get a hold of it,” says Karl Auerswald, Professor of Grassland Studies at the Technical University of Munich. Once incorporated, the material is broken down by bacteria within a very short time. Then the worms have none of it: “The earthworm cannot absorb it so quickly,” says Auerswald.
In addition, less air gets into a highly compacted soil. But: “Animals and plants also have to breathe,” says Auerswald. Because although the earthworm has no lungs, it needs oxygen, which it absorbs through the skin.
Therefore, there are fewer and fewer worms in arable soils, which further accelerates their erosion. The animals usually ensure water drainage into the depths through their tunnels. “A few hundred earthworms live in one cubic meter of healthy soil, that really matters,” says Auerswald.
The “buffer” is almost used up
The precious resource soil is therefore becoming scarce. Only 0.1 millimeters of new soil is formed every year. On arable land, however, the erosion caused by tillage and erosion is ten to a hundred times higher. “Ever since I was a student, there have been warnings about erosion and compression. Now I am at the end of my career and nothing has happened,” complains the 66-year-old.
According to Auerswald, a mixture of economic factors, convenience and short-term thinking is responsible. “The industry wants to sell big machines.” And the vehicles also find buyers: “It’s the same as with the SUVs, with farmers the tractor is a status symbol.” At the same time, it is relatively easy to fix problems these days, but this often creates new ones. “If the field is too wet, I just drain it. But maybe the field was the water reservoir for the environment, and it is then too dry,” says Auerswald, citing an example of short-sighted action.
The unsuccessful land policy also played its part in the increasingly severe dry spells, said Auerswald. Today it rains significantly less than before, in other phases it rains even more. The healthier the soil, the better it cushions such fluctuations, explains Auerswald – “it is our buffer”. When it rains, the water seeps into the deeper layers of the soil and is stored there. It is then released again in dry times. But Auerswald warns: “We treated this buffer badly, even though we urgently need it for climate change.”
Developments such as soil sealing through settlement, drainage of the landscape through roads and the draining of natural wetlands are added to the densification. In principle, the soil has been suffering for 200 years. In the last few decades, however, the problems have increased significantly. Current efforts to take selective countermeasures are a “drop in the ocean” for Auerswald. The Soil Protection Act, which came into force in 1999, also falls into this category for him: “A toothless tiger is still dangerous,” he says. “I don’t know of anyone convicted of soil erosion.”
One way to explore life in the ground is to listen to the sounds it makes.
(Photo: Biovision)
One of the goals of eco-acoustics is to better recognize, understand and experience all of these problems. In 2018, for example, researchers at ETH Zurich examined the noises made by the floor in the laboratory. In doing so, they not only detected the sounds of burrowing earthworms, but even those of roots that bored into a sandy substrate.
In the meantime, the scientists have already gone one step further: “We intend to use the acoustic emissions to follow the formation of the soil structure,” says Marine Lacoste, agricultural scientist and author of the study. This also includes physical processes, “we also consider, for example, the influence of the climate through wet and dry periods”. The compression could possibly also be made audible: “Compression leads to the movement of earth particles, we suspect that this generates noise.” The principle would be the same as with worms and plants, whose noises are also caused by friction.
As with Sounding Soil, Lacoste and her colleagues are faced with the problem of identifying the various noises and assigning them clearly to their originators: “We haven’t made it yet.”