artificial soil: quick and dirty

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SANDRA IVANY/OSF www.newscientist.com 11 August 2007 | NewScientist | 33 The Earth is being skinned alive – we need to make more topsoil, and fast, says Jessica Marshall Quick and dirty YOU might think it’s as common as muck. Dirt cheap, even. In fact, the soil beneath our feet is anything but. Good, fertile topsoil is crucial for 97 per cent of the world’s food supply, and without it parks and gardens would look more brown than green. So it’s a worry that soil has joined the long list of resources that are beginning to run out – and there is no natural way to replace it in our lifetime. But soon there might be. By mixing together a bit of animal, vegetable and mineral, researchers are turning waste into fertile ground.

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Page 1: Artificial soil: quick and dirty

SAND

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ANY/

OSF

www.newscientist.com 11 August 2007 | NewScientist | 33

The Earth is being skinned alive – we need to make

more topsoil, and fast, says Jessica Marshall

Quick and dirty ●

YOU might think it’s as common as muck. Dirt cheap, even. In fact, the soil beneath our feet is anything but.

Good, fertile topsoil is crucial for 97 per cent of the world’s food supply, and without it parks and gardens would look more brown than green. So it’s a worry that soil has joined the long list of resources that are beginning to run out – and there is no natural way to replace it in our lifetime. But soon there might be. By mixing together a bit of animal, vegetable and mineral, researchers are turning waste into fertile ground.

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Page 2: Artificial soil: quick and dirty

Making soil is a complicated business. In

nature it develops when weathered rock and

decomposing plant and animal material are

mixed and broken down by plant roots, soil

fauna, microbes and fungi. Over hundreds

of years, if the chemical and biological mix

is right, the raw ingredients are transformed

into a rich and complex substance with just

the right balance of structure, nutrients and

porosity to sustain plant life.

Understanding the process is one thing;

making the stuff from scratch is quite

another. Nevertheless, it looks like we will

have to find a way. Natural topsoils are being

scraped away by the truckload for use in

landscaping and construction projects,

putting pressure on natural supplies.

Humankind has faced soil crises before,

says David Montgomery, a geomorphologist

at the University of Washington in Seattle and

author of Dirt: The erosion of civilizations . Montgomery argues that the ancient

civilisations of Greece and Rome declined

along with their topsoil. He warns that the

world’s soil is now being eroded at least 20

times as fast as it can regenerate.

Preventing soil erosion and degradation

is one way to slow this trend. Improving the

quality of poor soil by adding organic matter

and minerals, or altering soil acidity, is

another. But while such tinkering can improve

bad soil, sometimes you just need more dirt.

Faced with expensive and ever-scarcer

topsoil supplies, researchers are trying to

mimic the natural process of soil formation

on vastly shortened timescales, using recycled

road aggregate, coal shale or ash mixed with

compost and other waste biomass.

Jody Tishmack started digging into

soil-making at Purdue University in West

Lafayette, Indiana, in the mid-1990s. The

university was looking for ways to recycle the

coal ash produced in the campus power plant

and also needed large quantities of topsoil for

landscaping. She had heard that fly ash – fine

particles given off when coal is burned – could

be used to improve soil. She wondered if she

could she kill two birds with one stone.

To create her new soil, Tishmack needed a

source of organic matter to mix with the coal

ash. As luck would have it, pharmaceutical

giant Eli Lilly had a production plant nearby

34 | NewScientist | 11 August 2007 www.newscientist.com

“The world’s soil is being eroded at least 20 times times as fast as it can regenerate”

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Page 3: Artificial soil: quick and dirty

with a ready supply of used fungal mats –

an extremely rich organic by-product of

antibiotics manufacture. The researchers

mixed the two waste materials – one mineral,

one organic – then threw in some wood chips

and leaves to add porosity, and composted

it all together. The result was an artificial

soil that Purdue used around its campus.

“Thousands of tonnes of this material were

made,” says soil chemist Cliff Johnston, who

worked with Tishmack on the project.

The endeavour led to Soilmaker, a spin-off

company that Tishmack still runs. The

company no longer uses Eli Lilly’s bio-sludge

or the coal-derived fly ash: the sludge smelled

too unpleasant as it composted and Purdue’s

power plant switched to a coal whose fly ash

contained too much arsenic to be safely put

in soil. Now Soilmaker mixes leftovers from

cornstarch production to supply organic

material while clay dug up in construction

projects provides the mineral component.

Others are trying similar approaches.

Richard Haynes at the University of

Queensland, Australia, is trialling a mix of fly

ash and chicken litter, composted together

with tree and garden waste, as part of a

government and industry-sponsored effort

to turn waste into new soil. As the ingredients

react, the organic material binds to the

minerals, forming aggregates that provide the

soil with a good pore structure. “Topsoil is

about 50 per cent pore space,” Haynes says.

That’s why using compost with no mineral

component is only a short-term solution. “It

loses its volume over time,” he says.

Trying to turn industrial waste into soil

can be problematic, with contamination a key

concern. Biosolids from sewage treatment

plants may be a good source of organic matter,

for example, but they can contain a lot of

potentially toxic heavy metals. Fly ash can

also have high concentrations of boron, which

is toxic to plants, and arsenic.

Kimberley Neville, formerly an

environmental geologist at Imperial

College London and now an environmental

consultant at the URS Corporation, also in

London, found that plants grown in soil

made from shale left over from coal mining,

iron-rich ochre from mine drainage and

composted sewage sludge had levels of arsenic

and zinc slightly in excess of UK safety limits.

“You might not want to grow food in it,” she

says, but she was looking at this material for

use in urban landscaping.

Montgomery, for his part, is uneasy about

using waste to make soil. “I could see how it

could be done well, but the potential is there

for it to be done poorly,” he says. “One of the

silliest things we can do is mix toxic waste

with soil. For materials that have high

concentrations of heavy metals, that’s

basically just poisoning the earth.”

Nevertheless, all of these projects

demonstrate a proof of principle that, should

all else fail, it will be possible to make fertile

soil from the right mix of ingredients. And

one day that might just save us from the fate

of the ancient Greeks. ●

Jessica Marshall is a freelance science writer based in St Paul, Minnesota

www.newscientist.com 11 August 2007 | NewScientist | 35

Soil in spaceWhen the time comes to set up

camp on the moon or Mars, we

won’t be able to rely indefinitely

on food shipments from Earth.

Nor, of course, will we be able

to just plant rows of crops in the

Martian soil and expect them to

grow. So frontier colonies will

need another food solution.

One possibility would be to

grow crops in nutrient solutions

instead of soil, but that has

drawbacks too. “Hydroponics is a

great way to grow plants, but it’s

cumbersome,” says Douglas Ming

of NASA’s Johnson Space Center

in Houston, Texas. “It’s tough to

control water in the microgravity

environment of space.”

So NASA scientists have

developed an artificial soil that

may be able to use moon or

Martian materials as one of its

ingredients.

The “space soil” resembles

cat litter in both appearance

and character. Both make use of

zeolites – porous minerals that

can absorb large quantities of

water. There are reasons to believe

they may exist on the moon or

Mars in large quantities. Zeolites

can also store positive ions,

including key plant nutrients such

as ammonium and potassium

ions. Another component of the

space soil is the phosphorus-

containing mineral apatite, which

NASA synthesised to incorporate

essential plant nutrients and to

dissolve at a desired rate.

The advantage of the artificial

soil is that the nutrients remain

bound up in it until the plants

need them, so they can’t wash

away, Ming says. NASA tested its

soil on a number of plants that

might make up a space diet –

those with high ratios of edible to

inedible biomass, such as sweet

potatoes and wheat, plus some

treats like strawberries. The plants

took to it just fine. “By providing

lots of light and optimal carbon

dioxide levels, we were able to

outdo field production by many

times,” says Don Henninger, who

led the project.

Until we’re ready to grow

potatoes on the moon, space soil

has found applications close to

home. The Colorado company

Zeoponix has licensed the

technology as a low-leaching,

well-draining soil improver for

athletics fields and golf courses.

RON

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RUGG

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Overworking soil can play havoc with its

structure and fertility

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