THE EARTH'S UNCERTAIN oil reserves and dwindling freshwater supply may get all the attention, but modern society is also overtaxing the ground itself.
At the same time that a growing population and the newfound appetites of the global middle class are straining our food supply, governments all over the world are also pushing for more ethanol-generating energy crops. To support all that production on a limited amount of arable land, scientists and farmers have long focused on technical improvements such as plant breeding, bioengineering, and creating new fertilizers and pesticides.
But some are now asking a different question: What if we could create better dirt?
An increasing number of scientists are starting to emphasize the extent to which soil - even more than petroleum or water or air - is a limited and fragile resource. Managing it better, and even improving it, will be vital to any equation that allows the earth to support the more than 9 billion people the UN estimates will live on the planet by midcentury.
The most dramatic research is still in the early stages, but soil specialists already have developed farming techniques that maintain and temporarily enhance the nutrient content of soil. Scientists in Australia and the United States have started making rich new earth from industrial waste, and research into the astonishing fertility of a mysterious Amazonian soil may lead to an additive that can boost the power of soil for thousands of years.
"A few decades ago, the philosophy was, 'Well, if your soil's degraded, just put some more fertilizer on, or till it another time and you can get the same crop yield,' " says David Laird, a soil scientist at the USDA's National Soil Tilth Laboratory. "Now there is growing interest in putting together systems that enhance the actual quality of the soil itself."
Dirt remains, in certain ways, a puzzle: Despite its seeming simplicity, it is a complex system whose fertility arises from the interaction of myriad physical, biological, and chemical properties. Even the most advanced current research doesn't claim to be able to synthesize enough of it for use on a global scale.
Nevertheless, progress in the science of soil has the potential to be truly transformative, and to help solve some of the biggest problems the planet faces. By 2050, according to Rattan Lal, a professor of soil science at Ohio State University, "All the necessities of food, feed, fiber, and fuel are going to be met by less than one-tenth of an acre per person, on average. And we already have seriously degraded a lot of the available land. So unless you can restore some of it you will just run out."
Soil does not arise quickly. In nature it starts with a layer of glacial grit, or windblown sand, or cooled lava, or alluvial silt, or some other crumbled mineral matter. A few pioneer plants put down shallow roots, and living things begin to make their homes in and on the surface, enriching it with their excrement, and enriching it further when they die and rot. The resulting organic matter feeds a whole underground ecology that aerates the soil, fixes nutrients, and makes it more hospitable for plant life, and over time the process feeds back on itself. If the soil doesn't wash away or get parched by drought, it very gradually thickens. It takes tens of thousands of years to make 6 inches of topsoil.
Because of all the things human beings do to it, University of Washington geologist David Montgomery has calculated, the world today is losing soil 10 to 20 times faster than it is replenishing it. In some places it is happening much faster: Sub-Saharan Africa, Northern China, parts of the American West, and Australia are already seeing large tracts of arable land disappear.
In his book, "Dirt: The Erosion of Civilizations," Montgomery traces the decline of numerous early societies, including classical Greece, imperial Rome, various Pacific Island cultures, and the Mayans, to poor management of their soil.
However, it has also happened that civilizations have improved their dirt. Among the world's richer soils is terra preta, the "black earth" found in certain swaths of the
In the last few years, archeologists have established something else intriguing about terra preta: it is man-made. It contains high concentrations of charcoal, along with organic matter such as manure and fish bones - essentially the household trash of a pre-Columbian society practicing a distinctive brand of slash-and-burn agriculture.
Researchers trying to replicate the fertility of terra preta have concluded that its secret is in the charcoal. Work by soil scientists like Laird, Johannes Lehmann of Cornell, and Mingxin Guo of Delaware State University suggests that the benefits of supplementing soil with charcoal - which they call "biochar" to distinguish it from the fuel of backyard barbecues - could be dramatic, widespread, and durable. Biochar, they have found, enhances the retention of water and nutrients, decreases the need for fertilizer, encourages microbial growth, and allows more air to reach crop roots. It also breaks down at a far slower rate than traditional fertilizers and soil additives. Depending on how the charcoal is made and applied, estimates of its life span range from decades to millennia. Scientists believe that some Amazonian terra preta soils are at least 2,000 years old.
"Biochar is much more effective at doing all the great things that normal organic matter usually does in soil, but it does it in much more effective ways, and it does it in a much longer way," says Lehmann.
Soil scientists have been experimenting with biochar for just a few years - barely enough time to see how well it performs over repeated plantings. Even its champions concede that there's plenty we need to learn about how to produce it on a mass scale. Researchers today are looking at how it might best be applied to the soil: in a dust, perhaps, or in pellets, or in a slurry mixed with manure. Two American companies, Eprida and BEST Energies, are working on bringing it to market.
Other scientists are looking at an even more ambitious project: making new soil from scratch. The challenge is to make truly synthetic soil that matches the stability and longevity of natural topsoil. (The artificial soils sold by the bag at gardening stores tend to be either natural soil that has been enriched, or potting soil, which is mostly compost and quickly degrades.)
Dick Haynes, a soil scientist at Australia's University of Queensland, has created a synthetic soil from industrial waste products: fly ash from power plants and byproducts of aluminum processing for its mineral components, poultry litter and manure for its organic matter. Haynes has said he wants to launch a soil-making industry in Australia, a country that has seen its limited fertile soil threatened by a decade-long drought. He hopes to have a product on the market within a few years.
Though Haynes has described his dirt as the world's first artificial soil, there are some precedents. In the mid-1990s, a Purdue University engineering graduate student named Jody Tishmack created a similar soil from power plant waste, biosolids left over from antibiotics production at a nearby Eli Lilly plant, and animal bedding from the veterinary school. The university used it for reclamation and landscaping projects around campus.
Today, Tishmack is still working on artificial soil, and her experience illustrates a key obstacle to its widespread adoption: cost. Synthetic soil is a very expensive way to replace a resource that is, however troubled, free.
She founded a company called Soilmaker, which uses a slightly less exotic recipe for its soil and sells it to gardeners and landscapers. Asked whether her product could work on an agricultural scale, she responded, "I can make it, but that doesn't mean that you can afford it. It would cost you $30,000 to put an acre of it down."
Until such methods are within reach of farmers, soil experts are focusing on ways that farmers can protect and even improve the soil they have.
One example is crop rotation, an ancient farming practice now seeing more use in both the developed and developing world. Instead of watching soil blow away from fallow fields between plantings, farmers are alternating grain crops with other crops so that the soil is covered at all times. And if those other crops are legumes like alfalfa, clover, or soybeans, they also take nitrogen out of the air and enrich the soil.
A twist on this idea, especially in tropical zones with poor soil, is agroforestry, in which fast-growing trees are interplanted with food crops - the tree roots stabilize the soil and pull up deep nutrients.
Another technique is to persuade farmers to stop tilling their ground entirely. Tilling, or plowing, is for most people synonymous with farming - traditionally it's been used to control weeds and mix fertilizer into the soil. But it also leaves soil far more susceptible to erosion, drying it out and leaving it bare to wind and rain.
To combat this, a growing number of American farmers are adopting "no-till" techniques, using machinery that inserts seeds through small slits into the ground. After the harvest, the crop remains are left on the field to decay, replenishing the soil in ways that synthetic fertilizers cannot.
Although techniques like no-till farming are gradually becoming mainstream practices, soil scientists remain frustrated by the lack of wider attention to the issue.
The loss of soil that feels so urgent to geologists averages out, over all the world's farmland, to just one millimeter per year. That rate is slow enough to create a political problem: It's outside the time frame of the politicians - and in many cases the farmers - who are key to fixing any problem as big as disappearing soil.
"Managing some of these slow-motion problems is the hardest because it never becomes a crisis," says Montgomery.
To soil scientists, the time horizon is only part of the political challenge. The larger problem may be, simply, that it remains hard for many people to take soil seriously.
"We put a value on the crops we harvest from the soil, but we don't think about the long-term benefit to the society of maintaining soil health and productivity," says Matt Liebman, a professor of agronomy at Iowa State. "It's much the same way we put a lot of value on medical treatments but very little on prevention."
Liebman points to the US Farm Bill as an example. Every year American farmers are heavily subsidized for commodity crops like corn, cotton, sorghum, and wheat that deplete soils, but are paid nearly nothing for those, like alfalfa, that help enrich it.
Ultimately, it may be the issue of climate change that drives public interest in soil.
As Daniel Hillel, a research scientist at Columbia University's Center for Climate Systems Research, points out, climate change is in part a soil problem. Carbon dioxide and nitrous oxide released from cultivated earth are in essence lost plant nutrients, and they're also major greenhouse gases.
Caring properly for soil, whether through additives like biochar or techniques like crop rotation and no-till agriculture, may have a serious role to play in mitigating greenhouse gases. Part of biochar's appeal, in fact, is that it keeps carbon locked up in soil for the many years the charcoal takes to break down. Currently, researchers at England's Newcastle University are working on a calcium-rich soil that they believe will have enhanced carbon-storing capacities.
If so, it would mean one more job for soil, a resource from which we already expect a lot - and which will underlie our ability to thrive in the centuries ahead.
"Maintaining your soil quality," says Laird, "is maintaining the viability of your society."
Drake Bennett is the staff writer for Ideas. E-mail firstname.lastname@example.org.