The Path To Better Soil  

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.