Click, crackle and pop: healthy soil makes more noise, scientists find | Soil

Ever wondered what the Earth sounds like? New research suggests healthy soil has a distinctive soundtrack of its own – the crackles, pops and clicks of ants and worms bustling around underground.

Scientists from Australia’s Flinders University listened to microphones planted in the ground to see if invertebrate instrumentals are a good indicator of biodiversity and soil health.

Land filled with plants and tiny animals carried diverse underground sounds, while cleared land only had bland white noise, they found.

“It’s a bit like going to the doctor,” the ecologist Dr Jake Robinson said. “They put a stethoscope on your chest, take a health check, listen to your beating heart … we’re doing something similar in the soil.”

He said the effectiveness of the microphone method could make it easier for researchers, conservationists and farmers to find and fix soil degradation.

Soil is home to more than half of Earth’s species and the source of nearly all of 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,” Robinson said.

Insects and other invertebrates build up soils, improve their nutrient content and prevent erosion, so their presence is a good indication of soil health. Soil full of worms carries low bubbly sounds, while lighter, six-legged ants make frequent higher-pitched clicks, Robinson said.

“A millipede has lots of tiny legs and they make little tapping sounds, whereas the snail has a more slimy glide sound,” he said.

Because the noises cannot be heard by the human ear, scientists 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 metres away and stand in silence.

“You have to stay super quiet, obviously, because you don’t want to create any confounding sounds,” Robinson said.

In the study published on Friday, Robinson and his colleagues reviewed hundreds of hours of recordings from 240 locations around Mount Bold in South Australia, near Adelaide, adding to previous research in the UK.

The new study confirmed the acoustic method worked just as well as traditional methods of checking soil health, which include expensive DNA testing or destructive methods such as digging up the soil or laying traps for invertebrates.

Dr Vanessa Pino, a soil scientist at the University of Sydney, said researchers would welcome the musical method.

“It requires a lot of effort to be sampling and counting invertebrates, so we’re always after ways to infer information in a more straightforward way,” she said.

The acoustic method is cheaper and less invasive, and may pave the way for back yard diversity testing. “We’re trying to democratise it, so everyone can just buy their own little recorder and microphone,” Robinson said.

Audio tech may even be able to improve soil health. Robinson’s forthcoming research found playing certain sound frequencies can speed up growth of fungi and bacteria that fend off plant diseases.

Future application of Robinson’s work could see the diverse soundscapes of healthy soil played back into degraded land to activate helpful fungal growth and rejuvenate the Earth.