Soils are the world's most pervasive ecosystems, and arguably its most complex and important. They’re home to more than half the planet’s species. But they’re also one of the ecosystems we know the least about.
We can see the surface, but short of digging endless holes, there’s remarkably little we can discover about what lies beneath.
No remote-sensing satellite can measure the moisture in soil, its carbon content, or its stockpile of nutrients. Even farmers are often operating blind, reliant on lessons from prior harvests.
But, if a small group of British researchers are right, the solution lies in seismology. Techniques developed to monitor earthquakes and look for oil can be harnessed to interrogate the structure of the world’s soils – cheaply, quickly and potentially on a global scale – for the first time.
Soon, the researchers say, they could be creating 3D maps of the world’s soils, using little more than hammer blows on a metal sheet and a mobile phone to hear the blows’ reverberations within the soil.
The revolutionary technique, which they dub ‘soilsmology’, could help farmers grow more crops while doing less environmental damage, aid governments in warding off famines, and allow scientists and climate negotiators to accurately measure the changing carbon content of the world’s soils.
The masterminds of the Earth Rover Program are currently at work on a handful of farms in England, Kenya and Colombia. Their aim is to create a “global soilcast” by surveying the soils that cover – and make fertile – much of Earth.
A drought of information
Soils are complex living entities, often compared to coral reefs in the ocean. They form over millennia as inert rock is broken down by weathering, allowing microbes and fungi to create organic matter that becomes a rich habitat for all manner of life.
“A teaspoon of healthy soil holds more living organisms than there are people on planet Earth,” says Dr Bruce Lascelles, a soil consultant and former president of the British Society of Soil Science.
But soils vary hugely, from the nutrient-rich black earths of Ukraine (which was, until recently, one of the world’s great cereal-growing and exporting regions), to crumbling drought-stricken sands on the fringe of the Sahara desert; and from the frozen soils of the Arctic tundra to the thin, nutrient-poor soils often exposed by tropical deforestation.
Without soil, there would be few plants on the land and nothing for us or animals to eat. Even in today’s industrialised farming systems, 99 per cent of humanity’s food is derived from plants growing in different kinds of soil.
Yet we know staggeringly little about these life-giving ecosystems. “Soils have long been the Cinderella of the sciences,” says Lascelles.
Soils are a blind spot for environmental regulators, too. We have national conservation laws and international treaties aimed at protecting biodiversity, the climate, forests, oceans and water and air quality. “But not soils,” says Lascelles.
Down the ages, farmers have learned, through trial and error, which soils will grow the biggest harvests. But there are still large gaps in their knowledge.
The fertility of soils from one field to the next – even one square metre to the next – can differ hugely. But exploring these differences scientifically to make the most of the land is often prohibitively expensive.
If farmers knew more, they could fine-tune their methods, cutting the need for expensive fertiliser, for instance, and avoid over-intensive cultivation that destroys their most precious resource.
It’s not just farmers who face an information drought. Soils are a major factor in the global carbon budget. They contain more than a third of the planet’s terrestrial carbon – three times more than the atmosphere.
But, unlike forests and other ecosystems, we have very little data on how soil carbon interacts with the atmosphere, and whether soils are contributing to climate change by releasing it, or helping prevent climate change by capturing it.
Indeed, soils remain, as a recent European Union report noted, “the hidden part of the climate cycle.”
What we do know is that soils are under threat as never before. They’re being widely eroded on farms by wind and water (especially after harvest when there’s no vegetation cover), as well as being damaged by compaction from heavy farm equipment.
More soils are eroded when forests and other natural vegetation is removed, or through overgrazing of grasslands by livestock.
Even without erosion, they’re under siege.
Intensive agriculture drains soils of nutrients such as nitrogen and phosphorus that are essential for plant growth.
Farmers try to replace lost nutrients with chemical fertilisers. But often they use too much, resulting in pollution and a decline in other vital soil features.
Many soils also suffer from other forms of pollution, such as industrial poisons like heavy metals, acid rain, a build-up of salt brought onto fields by irrigation water, and a rising tide of microplastics, which poison the organisms that sustain healthy soils.
About 40 per cent of the world’s soils are categorised as “degraded”, a figure that rises to 75 per cent in Europe. Every minute a further 20 hectares are reckoned to suffer, says Dr Rattan Lal of Ohio State University, an influential voice in the field of soil science.
Each year, some 75 billion tonnes of soil are presumed lost worldwide.
Some estimates suggest that the combination of poor farming and climate change could unleash some 50 billion tonnes of carbon into the atmosphere by 2050, accelerating global warming in a dangerous feedback loop that causes further soil-carbon loss.
Soils can recover in time, thanks to their living inhabitants. But it can take up to a thousand years to produce an inch of new soil. Lal calls soil degradation “a global public health emergency”, because the damage threatens the world’s ability to feed itself.
Ecologically, soil degradation is a “silent global crisis”, agrees Dr Harun Warui, an agroecologist at the Heinrich Böll Stiftung Foundation in Kenya.
So, whether our concern is the day-to-day management of individual fields, national planning for future food security, or using nature to help fix climate change, we badly need to know what’s going on beneath the surface of our soils.
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Ultrasound for the ground
Enter: a brand-new technique for mapping soils. Using seismology – the science of tracking sound waves through solid structures – researchers can find and assess key attributes such as a soil’s density, depth, moisture content and fertility.
The Earth Rover Program – the name is a nod to the high-tech NASA space rovers that explore the surfaces of other planets – is a collaboration between soil scientists and geophysicists more used to helping oil companies find hydrocarbons underground.
Its genesis came four years ago, when soil scientist Simon Jeffery of Harper Adams University was introduced to geophysicist Tarje Nissen-Meyer, then at Oxford and now at the University of Exeter, by environmental activist George Monbiot.
There was an instant meeting of minds. Nissen-Meyer was keen to find ways of using seismology to help heal the planet, rather than using it to find yet more oil. Jeffery was set on improving scientific understanding of the ecology of farm soils, to make their exploitation more sustainable.
The trio found a ready audience among other scientists, including British geographer Dr Andy Jarvis, the director of the billion-dollar Future of Food initiative at the Bezos Earth Fund (set up by former Amazon boss, Jeff Bezos).
Jarvis arranged for a $4m (almost £3m) grant from the Bezos fund, to help turn trials in tracking vibrations travelling through the ground into a system for globally mapping the layers, density, moisture and carbon content of the soil beneath our feet.
Currently, the system creates a seismic signal by tapping a hammer onto a small piece of ordinary metal on the ground and detecting the sound waves produced using several sensors placed nearby.
Jeffery likens the 3D soil maps his team are producing to ultrasound imaging of the human body. And the technique is just as quick. Each sounding takes just 10 seconds.
However, says Jeffery, “the plan is to develop the system such that in the future people will be able to place their mobile phone on the soil and walk around it, using their footsteps to generate the seismic signals and the accelerometer in their phones to collect and decipher them.”
Individual farmers will be able to map in 20 minutes what would once have taken several days and teams of diggers, he says.
The unique system is also cheap. In the past, a single sensor to measure seismic reverberations might cost around £700 (approx $940). But this expensive kit is redundant when every smartphone has an accelerometer that, with a simple app, can be turned into a seismological device.
Equipped with just their phone, says Jarvis, farmers could soon be able to “see exactly where to irrigate or fertilise; governments could monitor carbon stock transparently; and all of us could understand, at last, the living, breathing world underfoot.”
Soil's untapped potential
But taking measurements is just the start. The researchers are hoping to develop machine-learning techniques so that AI can extrapolate survey data to model entire landscapes.
Then forecasts can be created of how the soil might respond to current exploitation, new threats or, more hopefully, the better management that their soil data could help stimulate.
The Earth Rover manifesto puts it this way:
“As our insight deepens, we can strengthen the natural relationships between plants and microbes, enhance nutrient recycling, improve carbon stocks and reduce compaction, erosion and dependence on synthetic inputs. Thereby developing a new approach to farming that delivers higher yields with lower environmental impacts.”
Modern farming techniques such as robotics and remote navigation of farm equipment allow farmers to micromanage soil cultivation – potentially varying their inputs plant by plant.
But without the knowledge of what lies beneath the surface of their soils, these techniques can’t achieve anything like their full potential.
The plan is ultimately to sell the Earth Rover system to high-tech commercial farmers. The profits will then be used to enable cheap seismological analysis of soils for small farmers across the world.
For now, the researchers are testing techniques and monitoring soils on a handful of farms. On Roddy Hall’s turkey farm near Exeter in Devon, for instance, they’re watching how his organic methods, sustained over 30 years, improve soils.
Hall is delighted to be a guinea pig for the technology. “The soil is everything we do,” he says.
Seismology, he believes, will “deepen our understanding of the complexity of the soil. It’s terribly exciting and the machinery required is tiny, smaller than my phone.”
The team is also working on an agricultural research station in Colombia, a vineyard in France and on seven farms in Kenya, including several run by Forest Foods, a pioneering commercial regenerative farm company.
Dr Peter Mosongo, a soil scientist at the Centre for Ecosystem Restoration – Kenya (CERK), a partner in the work, says seismic surveys conducted by African farmers could transform livelihoods.
And back in the UK, at the Whixall Moss nature reserve in Shropshire, the research team has been demonstrating how seismology can dramatically improve estimates of how much carbon is stored in peat bogs.
This has major climate implications. Land covered in peat – the waterlogged remains of dead plants accumulated over many centuries – makes up just six per cent of world soils but often many metres deep, they hold around a third of soil carbon.
That’s the equivalent of decades of emissions from fossil-fuel burning.
Many countries with large peatlands want to enhance their carbon uptake by preventing destructive drainage, as a way to meet national carbon-reduction targets.
But to justify such an approach with international climate negotiators, they need good, solid data.
That’s hard to come by, though. Jeffery says there’s an almost five-fold difference in published estimates of the carbon in peatlands, because many are of unknown depth and density.
But now, simply by measuring the time taken for vibrations to bounce back from the rocks at the bottom of the peat, they can solve the puzzle and make their carbon-capture claims stick.
A major breakthrough
Many of the world’s top soil scientists are hailing soilsmology as a major breakthrough in their work. Lal says: “I strongly support the Earth Rover Program. Not only is the idea innovative and useful, but it also links farmers and communities with the most basic of all natural resources – the living soil.”
There are other means of transforming our knowledge of the world’s soils without endless digging, says Prof Alex McBratney, a Scottish soil scientist who is now director of the Institute of Agriculture of the University of Sydney.
Remote sensing is great for scanning the surface, and ground-penetrating radar can estimate soil thickness. Another trick is to send an electromagnetic pulse into the soil to measure its electrical conductivity, creating maps of moisture, clay content and salinity.
But all require expensive sensors, and they’re far less versatile than a simple hammer and mobile phone, which any farmer in the world could deploy to check their fields, and which allows global mapping of soils, says the Earth Rover crew.
An open-source global database of our most precious ecosystems is suddenly a realistic possibility.
For the first time, soils can be studied and managed as a global resource, a process vital to the survival of both nature and humanity.
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