ABC Listen.
Hello, Nige here.
And today on Imagine This, it's apple season.
There's lots of apple trees.
And there's lots of apples on the ground.
Yeah, I'm on a farm doing some picking.
Want to give me a hand?
Yeah.
Yeah.
Here's a good one.
Can I eat this?
Yeah, for sure.
Help yourself.
Yummy.
What else goes here?
Fruits.
Strawberry.
Yeah, there's strawberries, rhubarb, garlic and onions.
Pretty amazing.
It all comes from the ground under our feet.
From Julia.
And that's what today's question is all about.
Hi Nidge, I'm Evie and I am seven years old and I want to know how is soil made?
Hmm, that's a good question.
Soil is kind of everywhere, but where does it come from?
Maybe soil comes from plants and some because it maybe helps them grow.
Yeah.
Soil comes from insects.
Maybe.
Comes from the ground.
Maybe compost.
I think I need some brain food for this.
It's important to tune edge.
Oh no, there's no bin.
Just chuck it on the ground.
Isn't that littering?
Nah, it'll turn into soil like compost.
I need stuff like fruit, not plastic.
Are you sure?
I don't think soil is made of apple cores, is it?
Maybe.
I don't know.
We should ask a soil scientist.
Did someone say soil scientist?
Professor Sam Grover.
Hello.
Couldn't help but overhear your wonderful soil questions.
Sam leads the Soil, Atmosphere, Anthroposphere Lab at RMIT.
Anthroposphere.
No.
Sam and her team know all about the connections between soil, the environment and people.
That's right.
I can help you with those soil questions if you'd like.
Yes, please.
Hmm.
It'll take too long to get back to the lab, though.
So how about a bit of imagining instead?
Yeah.
We can follow Nige's apple core on its journey through the soil.
Ah, so I can put it on the ground.
It's not littering?
Well, I wouldn't chuck it anywhere, like on the road or a footpath.
But in some soil under this tree is just fine.
Pop it there, and let's imagine we're as small as an apple seed.
Everything is so ginormous and big.
The apple core is as big as a house.
And I don't think that I will be able to eat one.
Snitch, don't eat that.
Oh, gross.
What?
Now we're tiny, there's way more to eat.
But it's on the ground.
Come on, five second rule.
It still tastes good.
You're not the only one to think so.
Can you hear that?
It could be coming towards the tree.
It sounds like... It sounds like lots of feet.
It's a stampede!
Close.
It's a millipede.
Whoa, it's as big as a roller coaster.
It's a roller coaster, but it's a roller bug.
And it's going to take us for a ride.
Quick, jump on.
It's really bumpy everywhere.
The bumps in its back are like seats on the roller coaster.
Little critters like millipedes, worms, beetles and slaters are called detritivores or decomposers.
They're the clean up crew at this top layer of soil.
Something tells me they don't clean up with mops and vacuum cleaners.
Maybe something in their body just helps the soil to come into soil?
Yes.
Decomposers help decompose things.
They eat old bits of plants, like this apple core.
They'll eat other animals that have died.
Even poo.
That sounds disgusting.
Do they eat owl poo?
Remind me not to have dinner with a slater anytime soon.
Yucky to us, but vital for healthy soil.
Hang on tight.
We're going under.
Woo!
Yeehaw!
Looks like lots of tunnels.
Whoa, look out!
Earthworm on your right!
Yes, these tunnels made by worms and other insects are an important part of healthy soil because they let air, water and the roots of plants move through it.
Wow, there is so much life down here.
You have no idea.
There can be more life in just a single teaspoon of soil than there are human beings on Earth.
That's really cool.
I can see a worm, ants, millipedes, beetles.
I think I can see her.
Is that an earwig?
There's a lot of bugs.
I can't see billions though.
Where's everyone else?
You're about to find out.
What's that?
Larvae.
Bug babies.
Are they eating... Hey, is that my apple core?
It's too soon to be your apple core.
But they might be finishing off one that dropped off the tree a few weeks ago.
Maybe they eat food and then poo it out as soil?
Yes.
These larvae are making something called frass.
Frass?
It's basically poo.
Because I think it helps...
The plants grow.
That's right.
It looks like a dark powder, and it means that the trees and other plants can also get the nutrients from things like this apple.
So soil is made from apple cores.
It can be, yes.
Soil is lots of tiny bits of rock mixed with air and water and a dash of organic matter.
Organic matter?
So that's things that used to be alive, like old leaves, fruit that's fallen off trees, even animals and bugs that have died.
So soil is rock and water is dead stuff?
It's made of lots of alive stuff too, like these guys.
The bugs count as part of the soil?
For sure.
Soil's an ecosystem.
It's a community of all these alive and unalive things working together.
They're hungry babies.
Sure are.
They eat a lot and, well, they poo a lot too.
And that's where we're headed next.
Oh, no.
Oh yes, time to imagine being smaller than a baby.
Bugs bum.
Remember when you asked where everyone else was?
Well, here they are.
I can see bacteria, so many Yes.
At the microscopic level, soil is full of bacteria, fungi, archaea and viruses.
I can see billions now.
It's a microbial metropolis.
They're germs.
Don't viruses make you sick?
Some can, but most of the germs in soil are harmless to humans.
What are they all doing?
Well, this is the next layer of soil making.
Your apple core was eaten by bugs and then the bugs pooed it out, and now the microbes are eating the poo.
Ew, why?
Because it's good for their diet?
It's full of good soil stuff.
And then when they pull it out, it grows more grass?
That's right.
Germs break down the leftovers from the insects into their very smallest parts.
Elements like carbon, nitrogen, phosphorus.
What was that?
That sounded like thunder.
Must be raining up there.
Oh, muddy puddles.
Water is another important part of making soil.
Water from rain and rivers and even melted snow from mountaintops.
Over many, many years, it breaks down rocks into smaller and smaller pieces.
We've learnt about that.
It's called erosion.
Big rocks turn into sand, salt and tiny pieces.
They're called minerals.
The soil is kind of sparkly.
Are they the minerals from rocks?
Yes.
They're the smallest parts of a rock.
Cool.
What's happening over here?
It looks like all the nutrients are heading this way.
Careful, Nidge.
Don't get caught up in the... Help me!
A giant underground spider's got me in its web!
Save yourself!
It's not a spider web, Nidge.
It's called hyphae.
You've just tripped over in the mycelium.
It's not sticky.
Just stand up.
Oh, fuck.
I knew that.
What's mycelium?
It's like the roots of a fungus.
They spread through the soil and work a bit like a telephone for trees.
So the trees can talk to each other?
Kind of.
It's all about sharing nutrients.
Ring, ring.
Avocado tree here.
Hello, Avvo.
What can I do you for?
Got any sperm or nitrogen?
Ah, for sure.
Need any sugar while I'm at it?
No, thanks.
I'm free.
Helpful fungi.
Thank you, thank you.
I try my best.
Not you nerd, the fungus.
And this is all part of making soil?
Yes.
Remember how I said soil is a community?
Everyone we've met the millipedes, the microbes, the mycelium.
They're all working together moving nutrients through the soil to keep everything alive.
Everything?
Yes, even us.
We're getting sucked up by a tree's roots.
Up we go.
Hey, we're back to our normal size.
And we're sitting in the apple tree.
So we're back to where we started.
Yep, when a tree's roots are in healthy soil that's full of nutrients and mycelium, and bugs and good germs.
Water mixes it all together and the tree can drink it up through its roots.
It's what helps to make really healthy plants and super tasty fruit.
Like apples.
So my apple core became part of the tree again, to make more apples.
Yep.
It's a slow process, though.
It can take a hundred years to make just a few millimetres of healthy soil.
And it has a lot to do with what's happening on the surface.
What do you mean?
Well, soil often gets treated like dirt.
We need to look after our lovely soil just as much as we look after the sea or the sky.
You can throw banana peels in the compost and it makes nutrients to help the garden so it can grow.
Well, you could like get a worm farm and then put like lots of soil in there.
You can get a plant and get some soil and tuck it in nicely and smoothly.
Lovely.
It's fun to have a relationship with soil.
That might be gardening or composting or using soil for painting or making mud pies.
So, Evie, soil is made from lots of tiny bits of rock.
Like sand.
And sparkly minerals.
Mixed with air and water.
And lots of organic matter.
Apple cores.
Leaves.
And bugs.
First, decomposers like worms, beetles and millipedes munch it all up.
And then they poo it out to make what's called frass.
Then germs like bacteria and fungi break it down even more into even tinier stuff like nitrogen and phosphorus.
Plant food.
Nutrients.
These nutrients can then move through the soil with the help of water and mycelium.
Like a telephone for trees.
Helpful fungi.
Which helps to grow more things and make even more soil.
Healthy soil is a rich and bustling community.
It's a whole underground world.
Working hard to keep everything on land alive.
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