National Geographic's feature article this month is on soil - Our Good Earth: The future rests on the soil beneath our feet (via frogblog).

Journalists sometimes describe unsexy subjects as MEGO: My eyes glaze over. Alas, soil degradation is the essence of MEGO. Nonetheless, the stakes—and the opportunities—could hardly be higher, says Rattan Lal, a prominent soil scientist at Ohio State University. Researchers and ordinary farmers around the world are finding that even devastated soils can be restored. The payoff, Lal says, is the chance not only to fight hunger but also to attack problems like water scarcity and even global warming. Indeed, some researchers believe that global warming can be slowed significantly by using vast stores of carbon to reengineer the world’s bad soils. “Political stability, environmental quality, hunger, and poverty all have the same root,” Lal says. “In the long run, the solution to each is restoring the most basic of all resources, the soil.” ...

A black revolution might even help combat global warming. Agriculture accounts for more than one-eighth of humankind's production of greenhouse gases. Heavily plowed soil releases carbon dioxide as it exposes once buried organic matter. Sombroek argued that creating terra preta around the world would use so much carbon-rich charcoal that it could more than offset the release of soil carbon into the atmosphere. According to William I. Woods, a geographer and soil scientist at the University of Kansas, charcoal-rich terra preta has 10 or 20 times more carbon than typical tropical soils, and the carbon can be buried much deeper down. Rough calculations show that "the amount of carbon we can put into the soil is staggering," Woods says. Last year Cornell University soil scientist Johannes Lehmann estimated in Nature that simply converting residues from commercial forestry, fallow farm fields, and annual crops to charcoal could compensate for about a third of U.S. fossil-fuel emissions. Indeed, Lehmann and two colleagues have argued that humankind's use of fossil fuels worldwide could be wholly offset by storing carbon in terra preta nova.

Such hopes will not be easy to fulfill. Identifying the organisms associated with terra preta will be difficult. And nobody knows for sure how much carbon can be stored in soil—some studies suggest there may be a finite limit. But Woods believes that the odds of a payoff are good. "The world is going to hear a lot more about terra preta," he says.

Walking the roads on the farm hosting Wisconsin Farm Technology Days, it was easy for me to figure out what had worried Jethro Tull. Not Jethro Tull the 1970s rock band—Jethro Tull the agricultural reformer of the 18th century. Under my feet the prairie soil had been squashed by tractors and harvesters into a peculiar surface that felt like the poured-rubber flooring used around swimming pools. It was a modern version of a phenomenon noted by Tull: When farmers always plow in the same path, the ground becomes "trodden as hard as the Highway by the Cattle that draw the Harrows."

Tull knew the solution: Don't keep plowing in the same path. In fact, farmers are increasingly not using plows at all—a system called no-till farming. But their other machines continue to grow in size and weight. In Europe, soil compaction is thought to affect almost 130,000 square miles of farmland, and one expert suggests that the reduced harvests from compaction cost midwestern farmers in the U.S. $100 million in lost revenue every year.

The ultimate reason that compaction continues to afflict rich nations is the same reason that other forms of soil degradation afflict poor ones: Political and economic institutions are not set up to pay attention to soils. The Chinese officials who are rewarded for getting trees planted without concern about their survival are little different from the farmers in the Midwest who continue to use huge harvesters because they can't afford the labor to run several smaller machines.

Next to the compacted road on the Wisconsin farm was a demonstration of horse-drawn plowing. The earth curling up from the moldboard was dark, moist, refulgent—perfect midwestern topsoil. Photographer Jim Richardson got on his belly to capture it. He asked me to hunker down and hold a light. Soon we drew a small, puzzled crowd. Someone explained that we were looking at the soil. "What are they doing that for?" one woman asked loudly. In her voice I could hear the thought: MEGO.

When I told this story over the phone to David Montgomery, the University of Washington geologist, I could almost hear him shaking his head. "With eight billion people, we're going to have to start getting interested in soil," he said. "We're simply not going to be able to keep treating it like dirt."

The IHT has an article on soil depletion and how to mitigate it, mentioning biochar / terra preta as an option - Scientists focus on making better soil to help with food concerns.

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 like 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 nine billion people the United Nations estimates will live on the planet by mid-century.

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 National Soil Tilth Laboratory, part of the U.S. Department of Agriculture. "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 does not 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 does not wash away or get parched by drought, it very gradually thickens. It takes tens of thousands of years to make 15 centimeters of topsoil, about 6 inches' worth.

Because of all the things human beings do to it, a 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: northern China, sub-Saharan Africa, 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 ancient Greece, imperial Rome, various Pacific Island cultures and the Mayans - to poor management of their soil.

However, it has also happened that some civilizations have improved their dirt. Among the world's richer soils is terra preta, the "black earth" found in certain swaths of the Amazon basin. It is dark, loose and loamy, and unlike the pallid earth that characterizes most of the Amazon, it is strikingly fertile.

In the last few years, archaeologists 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 University, 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.

The Toronto Star has an interesting article on topsoil depletion and carbon emissions caused by our current system of industrial agriculture.

Like most city dwellers, my knowledge of farming is embarrassingly limited. But a conference on agriculture and global warming has inspired me to dig deeper (pun intended) into things rural. The speaker who grabbed my urban-oriented attention was American-born, U.K.-based Craig Sams, co-founder of Green and Black's organic chocolate bars. His message was, well, grounding.

"When we talk about food and farming we are talking about carbon," Sams pointed out. "The process by which food is made starts with carbon dioxide and nitrogen from the atmosphere and turns it into protein, fat, and carbohydrates. Plants conjure food out of thin air with help from water and sunshine ..." Even better: "Of all the carbon capture and storage technologies on the planet, none can ever hope to be more efficient than photosynthesis ... It's absurdly cheap and has been tested for millions of years ..."

Sadly, the brilliance of nature has been tarnished by the short-sightedness of humanity.

Sams was born on a farm in Nebraska. In the 1880s, when his great-grandfather first plowed the prairie, the topsoil was four metres deep. Now it's less than one metre and "shrinking." Every tonne of soil that Sams' great-grandfather plowed contained about 50 per cent carbon and 5 per cent nitrogen. During erosion, that tonne reacted with oxygen in the air and produced about three tons of carbon dioxide, along with the more damaging nitrous oxide – equivalent to another 30 tonnes of carbon dioxide.

Sams said that his great-grandfather lost about four tonnes of soil per acre annually, "so over 160 acres he emitted 21,000 tonnes of carbon dioxide from our little farm. Every year." That was in the days of horsepower. "In the 1930s, when oil sold for 10 cents a barrel and tractors began replacing horses, production went up, plows went deeper, and soil erosion went crazy." The result was the Dust Bowl.

Sams pointed out that half of the world's greenhouse gas emissions from 1850 to 1990 came from agricultural activity, but therein lies the good news. "There are 1.5 billion hectares of arable land on the planet and if you just saved one tonne of carbon emissions per year per hectare that would give us a 1.5 billion tonnes emission reduction. If you went further and instituted practices that captured and locked carbon in the soil, then you would have another 1.5 billion tonnes reduction, giving a total of 3 billion tonnes per year of carbon reduction."

This would cover more than half of the 80 per cent emissions reductions we need to stabilize our climate, he told us.