Listening to soil

MARY REICHARD, HOST: Today is Tuesday, April 15th.

Thank you for turning to WORLD Radio to help start your day.

Good morning. I’m Mary Reichard.

NICK EICHER, HOST: And I’m Nick Eicher.

Coming next on The World and Everything in It: Listening to the land.

For most of us, dirt is just something we dig in to plant flowers or rinse off after we do. But for a few researchers, it's the key to a healthier future. And what they found is there’s a relationship between the soundness of the soil and the sound of the soil.

WORLD’s Mary Muncy talked to some researchers trying to understand what’s going on below the surface.

JAKE ROBINSON: We're just heading down the hill now.

MARY MUNCY: Jake Robinson and his team are walking through the Australian bush near Flinders University, listening for loud soil.

ROBINSON: We're looking for insects really.

Robinson is a microbial and restoration ecologist: Basically, he studies microorganisms and how to restore damaged ecosystems. Right now, he’s doing that with sound. As a general rule, the louder the soil, the healthier it is.

ROBINSON: We'll go out, gather our equipment, head to the field, and, yeah, put the probes in the ground, set the recordings up, and gather the data.

So far this morning, they’ve tried a field and a termite mound, and it’s been pretty quiet.

ROBINSON: Let’s try near the lake.

CHRIS CANDO-DUMACELA: Yeah, there’s water there.

ROBINSON: Let’s do it.

That’s Chris Cando-Dumancela. Another researcher. South Australia is in the middle of drought, which means there’s lots of stressed and quiet soil.

ROBINSON: We're gonna place our probe under a rock. Now, it's a bit more… the microclimate is a bit more moist.

They put their headphones on and wait:

CANDO-DUMACELA: Still rather quiet.

ROBINSON: Still rather quiet here.

CANDO-DUMACELA: What am I hearing? A duck.

ROBINSON: The underground duck.

CANDO-DUMACELA: There are some different I reckon there's some subtle pops.

Maybe some clicks too.

CANDO-DUMACELA: There's no orchestra, but there's a couple of couple of instruments going.

Those instruments are mostly invertebrates digging, pushing, or skittering across the soil.

CANDO-DUMACELA: The majority of species on Earth lives in soil, they've literally formed the soil and creating all sorts of complex habitats.

Soil sound research is new. Cando-Dumancela, Robinson, and their team were some of the first people to publish a paper on it a few years ago.

They found that in general, when soil is healthy, it generates a diverse soundscape, full of pops, clicks, and sometimes slithery worm or snail sounds.

Back in the lab, Cando-Dumancela, Robinson, and other researchers try to figure out how to use that knowledge to help stimulate healthier soil.

ROBINSON: A bit like going to the doctors, where they might put a stethoscope on your chest, listening to your heart and your lungs and, you know, give you some health diagnostics. We're kind of trying to do the same thing for soil.

They’ve discovered that while loud soil is generally healthier than quiet soil, it isn’t necessarily the healthiest. Loud soil might just mean there are too many ants or too many worms. They have to analyze the types of sound to determine which species are actually there.

Often they sort through them with an algorithm, but you can hear worms pushing soil as they move.

ROBINSON: We're getting quite good at actually telling the difference between, say, a snail, compared to a worm, compared to a millipede, compared to a spider.

By some estimates, 40 percent of the world’s soil is degraded—meaning reduced biological or economic productivity—and just about all of life depends on that soil in some way, whether for food, a home, or both.

Sometimes the degradation happens through bad farming practices or things like noise, light, and chemical pollutants.

ROBINSON: It essentially changes the composition of the microbiome in the soil.

If soil’s microbiome is damaged, Robinson says there are a few ways to try to repair it.

One of those is trying to build up organic matter through compost or other natural soil amendments, and it’s possible that culturing bacteria to implant into the soil could work, too.

ROBINSON: Another experiment of ours is actually playing sounds to microorganisms, and it stimulates their growth.

One organism they’re working with is fungi that stimulate the growth of plants.

ROBINSON: We just experimented with a very kind of monotonous, monotone sound. It was eight kilohertz at 80 decibels. So that's the kind of the volume, the power of the sound, which is similar to a kind of urban street volume.

They’re not sure why, but it worked.

ROBINSON: Someone's put forward the hypothesis that fungi, fungi are the first things that colonize dead wood, you know, when trees fall in the forest. So they think they might have evolved a mechanism to detect the vibrations of trees hitting the ground so that they can then colonize those logs.

Other people think it might be about the same frequency as rain hitting the ground.

In any case, now they’re experimenting with different frequencies and volumes to see if they can stimulate more growth or even find sounds that inhibit pathogens.

Back in the field, Robinson and his team are done listening for today. They pack up their equipment and hike back to the university.

ROBINSON: There's a lot of symbiosis going on between the invisible and the visible world.

CANDO-DUMACELA: The knowledge we're getting out of this has completely changed the way that I speak to people about soil.

They say most people think of soil as dead… Something to build on or maybe play in, but Robinson says that besides the invertebrates, there are microbes in the soil that we can’t see or hear without equipment.

ROBINSON: We're kind of just, you know, highlighting the fact that soil is actually a living conglomerate of life.

Something Robinson says should be stewarded, not dominated.

ROBINSON: If you think of it more as like your family, I suppose then you know, you kind of have a responsibility to help each other out.

Reporting for WORLD, I’m Mary Muncy.

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