SOPHIE: Today I'm meeting a scientist
who researches soil health in our environment.
But she's also got a passion for helping home gardeners
understand their soil
and therefore understand their gardens.
I'm visiting Emily Leyden at her home in Adelaide's inner north.
Soil is one of the most underrated and little understood ecosystems
on our planet.
If you think about it, it helps feed us,
it helps clothe us,
it filters and cleans our water and regulates our atmosphere.
It really is a truly wondrous material.
Gardeners generally put most of their time and energy
into soil improvement in the veggie patch.
I know I certainly have,
and I actually brought some of my soil along to see what you think.
Wow, so this is really amazing soil.
It's light and it's fluffy,
and that means we'll be able to have good air exchange with the roots,
water will be able to get into the soil but also drain away.
And you've obviously put a lot of organic matter
into this over the years.
I certainly have!
So I guess gardeners have to remember
that soil improvement is an ongoing process.
Absolutely. It's not a once-off thing.
So after every crop, you really want to be thinking about
improving your soil with things like
composts and manures and cover crops.
So you're obviously a keen gardener.
Yes.
How important is it to understand soil to develop a good garden?
Well, understanding your soil texture and your soil type
is really important because it's gonna determine
what plants work best in your garden.
And it can also help you understand how you can improve your soil
to get the best out of those plants.
So when you want to look at the soil in your garden,
you really want to dig deep below the topsoil,
so about 30 or 40 centimetres deep.
There are a couple of simple tests that you can do in your garden
that don't require any kits, lab equipment or tools.
The first is to figure out what type of soil you have
with a simple soil-texture test.
So what is soil texture?
Well, when you're looking at your soil texture in your garden,
you want to determine whether you've got a sandy soil or a clay soil,
or in the middle is your loams.
And how do you tell if you've got sand or clay?
Well, really simply, you just grab some of your soil
into your hands.
So here I've got a sandy soil.
Just add some water.
And as you're doing that,
you're wanting to look at how that soil is coming together.
As you can see here with my sand,
it's taking a while to form into a ball.
It is hanging together a little bit,
but you can see how it's falling apart really easily.
And that gives us an indication that we have a sandy soil.
So, coarse particles. Coarse particles.
And so if we have this in our garden,
the things we need to be aware of
is that when you put water on, it's gonna drain really easily.
There's not much clay in here
that holds onto things like nutrients or water.
OK. So do you do the same with other sorts of soils?
Absolutely. So here I've got some soil from my garden.
So this would be classified as a loam,
and loams have equal quantities of sand, silt and clay.
And you just keep working it.
Keep working it till you've got a nice ball
that's not too wet and not too dry - just right.
What I'm gonna do now is I'm gonna try to make it into a ribbon.
And I do that by just rubbing it in my hands.
You can see it is still holding together,
but it does shear apart.
And you can see there. Mm-hm.
That means it's got some clay but not too much.
But it's also got sand, which is helping it break apart,
and also your silt.
And so this is a good balance
of all those three different types of soil particles -
sand, silt and clay.
That's loam. And we classify that as a loam.
OK, now what would happen if we did the same test with clay?
OK, so I've got a clay here,
and this is a clay, actually, from McLaren Vale,
a wine-growing region in South Australia.
So I'll do the same thing
and then start to add your water like we did with the other two.
Clay is notorious for feeling like plasticine in your hand
as you work it.
So what we do now, we've got a moist bit of soil
and we start to roll it out.
And you'll see, 'cause this is a clay,
we're not breaking apart very easily.
So that's obviously clay. OK. That's right.
'Cause we are able to make a really long sausage.
So once we know our soil texture, what comes next?
Well, no matter if you have a clay soil or a sandy soil,
it's very difficult to change that texture.
But what you can work on as a home gardener
is increasing your soil's structure,
and we do that through organic matter.
So organic matter is compost or aged animal manure?
Yeah, exactly.
So what organic matter does is, in a sandy soil,
it could help bring together those sand particles,
a bit like a glue, and helps form those groups
and that's what we want in a soil.
So is there a challenge with putting organic matter into sandy soils?
Yeah, there is.
You have to be a bit careful
because organic matter can form a coating on the sand
that can repel water.
We can overcome that with an organic-based wetting agent.
And also you can add some kaolin,
or bentonite clay can also help in this situation.
The next test is to find out if your soil is dispersive.
So you can see here we've got a non-dispersive,
a moderately and a highly dispersive soil,
and we tell that by the cloud that's formed around each one.
Cover your samples in some distilled water
and leave them to sit for an hour.
So in a highly dispersive soil,
what we've got is excess sodium.
When we put water on that has salt in it,
especially sodium salt,
the water goes through the soil
but the sodium hangs about on those soil particles.
And what it can do is it pushes apart the clay particles
and creates waterlogging and crusting problems.
OK, so in cases where the soil is dispersive,
that's where you can use gypsum and it's effective?
Gypsum is calcium,
and calcium replaces the sodium on the soil particles,
allowing it to leach away
and that can increase your soil's structure.
So learning about your soil isn't just about improving it, is it?
Well, improving your soil with organic matter
is always a good idea.
But, primarily, what you want to do is plant for your soil type,
so planting for sandy soils or planting for clay soils,
and that gives you the best chance of success.
Understanding the soil in our backyards
is really just the beginning.
The way we manage land here and around the world
has huge implications for our overall health.
We're destroying our soil at quite a high rate.
It takes up to a thousand years to build 10 centimetres of topsoil
and we don't have enough time to rebuild it.
So it's really important we start to value and appreciate
our soil resource.
In fact, it's actually vital for our very survival.