Ever wondered what the earth sounds like? New research suggests that healthy soil has a distinctive soundtrack of its own – the crackling, popping and clicking of ants and worms moving underground.
Scientists from Australia’s Flinders University listened to microphones planted in the ground to see if invertebrate instruments is a good indicator of biodiversity and soil health.
Ground filled with plants and small animals carried diverse underground sounds, while cleared land had only soft white noise, they found.
“It’s a bit like going to the doctor,” said ecologist Dr Jake Robinson. “They put a stethoscope on your chest, take a health check, listen to your beating heart… we do something similar in the ground.”
He said the effectiveness of the microphone method could make it easier for researchers, conservationists and farmers to find and correct land degradation.
Listen to healthy soil
Soil is home to more than half of Earth’s species and the source of almost all the planet’s food but more than 75% of soils around the world are degraded, according to Unesco.
“Restoring and monitoring soil biodiversity has never been more important,” said Robinson.
Listen to low-lying ground
Insects and other invertebrates build up soil, improve its nutrient content and prevent erosion, so their presence is a good indication of soil health. Soil full of worms carries low bubbling sounds, while lighter, six-legged ants often make higher-pitched clicks, Robinson said.
“A millipede has very small legs and they make little tapping noises, whereas the snail has a more slimy sliding sound,” he said.
Because the sounds cannot be heard by the human ear, scientists have set up microphones that pick up vibrations from contact with the dirt – then amplify the recording by 20 decibels. After placing the microphone, researchers move 20 meters away and stand in silence.
“You obviously have to stay very quiet because you don’t want to create any confusing sounds,” Robinson said.
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In the study published on Friday, Robinson and his colleagues took hundreds of hours of recordings from 240 locations around Mount Bold in South Australianear Adelaide, adding to previous research in the UK.
The new study confirmed that the acoustic method worked just as well as traditional methods of checking soil health, which include expensive DNA tests or destructive methods, such as digging up the soil or laying traps for invertebrates.
Dr Vanessa Pino, a geologist at the University of Sydney, said researchers would welcome the musical method.
“It takes a lot of effort to take and count invertebrates, so we’re always looking for ways to derive information in a more simple way,” she said.
The acoustic method is cheaper and less invasive, and could pave the way for backyard diversity testing. “We’re trying to democratize it, so everybody can just buy their own little recorder and microphone,” Robinson said.
Audio technology can even improve soil health. Robinson’s upcoming research has found that playing certain sound frequencies can speed up the growth of fungi and bacteria that ward off plant diseases.
Future application of Robinson’s work could play the diverse soundscapes of healthy soil back into degraded land to activate beneficial fungal growth and rejuvenate the earth.
