The sound of the worm is a distinctive growling and rustling. The ants resemble the soothing patter of rain. A passing, burrowing field mouse makes a sound like a squeaky dog toy being constantly chewed.
On a spring day at Rothamsted Research, an agricultural research institution in Herefordshire, skylarks and the M1 motorway compete for airways. But the attention here is on the soundscapes underfoot: a rich ecosystem with its own alien sounds. More than half of the planet’s species live in soil, and we’re just beginning to understand what they’re doing. Insect larvae, millipedes, centipedes and woodlice have other sound signatures, and scientists are trying to figure out which sound comes from which creature.
In an area divided into test strips, Carlos Abrahams pushes a sensor the length of a knitting needle into the ground. Wearing a pair of headphones, he listens to the “poor man’s rainforest”: a dark landscape of miniature caves, tunnels, and rotting matter boiling beneath our feet.
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“There are a few ticks and clicks,” says echoacoustic expert Abrahams of Baker Consultants, as he listens to them.
Abrahams and scientists from the University of Warwick are building libraries of underground sounds. The earth makes different sounds depending on the season and whether it is day or night. Research shows that sounds become richer even in the afternoon when the ground warms.
Dr. from the Crop Center at the University of Warwick. “Soil is so mysterious,” says Jacqueline Stroud. “It’s like opening the door and seeing what’s going on underground. “It’s a different way to explore the world.”
Until recently, soil was a relative blank spot for monitoring species abundance. Farmers and gardeners hoping to find out how healthy their soil is have had to do shovelfuls of digging and painstaking testing.
A study last year found that soil is the single most species-rich habitat on Earth, with more than half of all species living in it. But only some have been detected, and most are too small to see. Soundscapes are becoming an increasingly popular way to view the abundance of wildlife above, below ground and underwater.
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Noisy soil is generally healthier because it has more insects and worms moving around. Soil organisms change and improve the structure of the soil by passing nutrients between each other and creating a well-ventilated and diverse environment. These networks provide people with food, fiber, and clean water; Topsoil is where 95% of the planet’s food is grown.
Soils with less biodiversity are more fragile: they have lost the structure and connections that hold particles together. This means they are more likely to be washed away by floods or blown away by strong winds. An estimated 24 billion tonnes of fertile soil is lost each year due to intensive agriculture, according to the UN-backed Global Land Outlook study.
Relating to: ‘Vital to look after the soil’: Fears over UK earthworm population decline
Farmers have repeatedly requested more effective ways to measure the abundance of earthworms, a good indicator of soil health, according to the researchers.
Baker Consultants and the University of Warwick have funding for a two-year research project developing a recording unit prototype. The aim is to record soil sounds on a “big data” scale.
On the land Abrahams is testing, scientists are experimenting with more ecological farming methods, including crop rotation with legumes and a higher proportion of oats. In total, 70 scientists work on this small plot of land, divided into 66 plots of 24 m by 24 m; It is discovering new things about the structure of soil, viruses, microbes and fungi, making it one of the most studied soils in the world. “This is a unique open-air laboratory,” says Kim Hammond-Kosack of Rothamsted Research, which organized the experiments.
Abrahams and Stroud’s teams began their sampling efforts in Rothamsted in October last year. They take two recordings at each site each month and measure how activity above ground affects what’s happening in the soil.
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Dr Simon Butler from the University of East Anglia listens to soil before and after application of zebra manure in Eswatini (previously known as Swaziland). After application, the soil gushed with activity. “I never really considered the sound of soil, so it was fascinating to hear how the acoustic properties changed in response to the presence of fresh manure,” he says.
Since the sounds produced are in the lower range of human hearing, it is possible that there are sounds in the soil that we have not yet heard. Initial research conducted in Switzerland shows that soils produce the most complex sounds in spring and summer, while these sounds decrease in autumn and winter. Abrahams’ previous research showed that soils in restored forests in the UK had greater sonic diversity than soils in deforested areas. “As a general rule, the more diversity there is above ground, the more there is in the soil,” says He.
In January, researchers published what they believe is the first paper examining tropical forest soils, which are among the most biodiverse habitats on Earth. Like others, they documented multiple mysterious sounds. The next task is to create a library of earth sounds so they can decipher what they are actually listening to.
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