Tayside and Central Scotland

Model helps reveal soil's secrets

Media captionA university team is using X-ray scanning of soil samples to reveal for the first time the places where life thrives below ground

It looks like the world's largest sugar cube. Or perhaps a pale, unsuccessful imitation of Spongebob Squarepants.

But it holds the key to a hidden world beneath our feet.

It's a 3D-printed model of soil, a large plastic cube full of holes. So many holes that even an Emmental cheese would raise the white flag. And the holes are what matter here.

Except at the Scottish Informatics, Mathematics, Biology, and Statistics (SIMBIOS) Centre at Dundee's Abertay University they don't call them holes.

They're pores, the spaces between the soil's minerals where underground life can thrive. Life like bacteria, fungi and worms.

Prof Wilfred Otten says there are as many life forms in a handful of soil as there are humans on Earth. And everything - from flooding to food production - depends on the soil.

He says previous methods of studying soil structure have been like examining architecture by looking at a pile of rubble.

Life and pores

The SIMBIOS solution? Put soil samples in an X-ray computed tomography (CT) scanner.

"When we take a soil sample that comes out of the field," Prof Otten says, "people don't realise that this is full of life and full of pores.

"What we really want to know is how does this look on the inside. So we place this in the X-ray tomography machine."

Image caption Researchers have been using a 3D printed model of soil

He's holding a cylindrical sample a little smaller than a can of beans.

"And then our X-rays will go through the sample," he adds.

By taking 3,000 X-ray slices through the sample, a 3D model of the soil can be computed.

The on-screen animations the scans create are things of beauty in themselves. The 3D simulations spin on the screen, the soil stripped away to show the pores in between like a tiny, complex cave system.

The pores are colour coded to show how they interconnect - or don't, as the case may be. And that reveals how life forms in the soil can compete or cooperate.

The team has taken things one step further by working with colleagues at Nottingham University to 3D print plastic models of soil samples. Hence the unsuccessful Squarebob, a larger-than-life model of a cube of soil.

Soil simulator

However another of the researchers, Dr Ruth Falconer, puts the large model to one side and picks up a smaller version. Just as pale, just as full of holes, but this time actual size.

It is, in effect, a soil simulator.

"This is a few centimetres cubed", she says, "and we can actually change the properties of the surface of the material and inoculate it with different microbes.

"We're predominantly interested in fungi, and fungi are common plant pathogens. And we're interested in bio-control agents.

"So we can seed these structures with different types of fungi and look at species interactions and how the complex pore network basically governs those interactions."

Image caption A greater understanding of soil could make it more productive

Some might think this is a lot of technology to unleash on some humble dirt. But Prof Otten says soil has never been more important for all of us.

"We are running out of soils in a time that we need to produce more food," he says.

"So there are huge problems there and we need to manage our soils sustainably. And up to now we have not been successful in doing that. Therein lies the problem.

"One of the reasons we believe that problem is there is that we've treated soils too much like a black box.

"We were not really able to look inside what soil really looks like.

"What's so exciting about science these days is that we now have novel technologies to look at those very complicated systems in a new way."

The professor says just one per cent of the surface area of soil pores currently supports microorganisms. So if a way could be found of increasing that by just another percentage point the productivity of soil could double.

Meanwhile, by employing a multidisciplinary approach combining informatics, maths, biology, physics and statistics, Dr Otten and his team are expanding our understanding of the microscopic world that lies hidden down in the dirt.

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