Deep, Down and Dirty: The Science of Soil Page #6

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Here, they're using cutting edge

technology to examine soil

on an incredibly small scale.

We're joined by Evelyne Delbos,

operator of the Scanning Electron

Microscope at the Hutton Institute.

She's looking at soil

magnified 400 times.

I have the three main

parts of the soil.

The sand grains here.

On the right is the silt

and the clay at the bottom.

Well, you can sort of see with

the clay, for example,

it's stacked so tightly together

that you can actually not see

discernible gaps between them.

Whereas here we've got these very

large sand particles

and even through they're

right on top of each other

you can still see the far larger

gaps.

That allows air,

for aeration of the soil,

and it also allows water movement

through the soil.

But there's more going on here

than just how the particles

are packed together.

Let's imagine this is

a grain of sand.

And the surface area of that

grain of sand is that surface,

that surface, that surface,

and that's it.

It we take, by comparison,

the same volume of clay

then you have that surface plus that

surface plus that surface, so you

can imagine already that the surface

area is much, much, much larger.

So what does the surface area

do to the water?

What's the relationship

between those two things?

What's interesting about many clays,

it has an electric charge

associated with its surfaces.

Many nutrients that are dissolved

within the water can be

attracted to these clay sites, to

this large surface area,

and then held,

basically for root systems

then to uptake for plant growth.

So clay particles have an electrical

charge that can bind nutrients

and water to them.

This allows soil to

act as both larder

and reservoir for plants

and animals.

Sounds ideal, but there's a catch.

Too much clay and the soil can act

like a sponge

and can quickly become waterlogged.

At the other end of the scale,

too much sand

and the water can run through

too quickly,

washing the nutrients out and

leaving behind soil that's dry.

Have we got an image of what

a good soil should look like?

Here you can see some grains

of sand, they are different sizes.

It's a mixture and you can also have

there and there the clay

and the silt all mixed up.

So this is demonstrating the ideal,

in terms of soil. It would

be free draining,

retain sufficient moisture,

sufficient nutrients,

what about microbial activity?

This is a very,

very complicated 3D structure

which gives all of the microbiota

within the soil effectively a niche,

a home to live, and as a result

the ecosystems that exist in the soil

are exceptionally complicated.

This is a classic example where

you've got the mix between the

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