artificial soil: quick and dirty
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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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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”
PUNC
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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
NIEB
RUGG
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Overworking soil can play havoc with its
structure and fertility
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