via Frank Strie
A section from the big story about Soil:
http://ngm.nationalgeographic.com/2008/09/soil/mann-text/8
Our Good Earth
The future rests on the soil beneath our feet.
By Charles C. Mann
Photograph by Jim Richardson
Wim Sombroek learned about soil as a child, during the hongerwinter—the Dutch wartime famine of 1944-45, in which 20,000 or more people died. His family survived on the harvest from a minute plot of plaggen soil: land enriched by generations of careful fertilization. If his ancestors hadn’t taken care of their land, he once told me, the whole family might have died.
In the 1950s, early in his career as a soil scientist, Sombroek journeyed to Amazonia. To his amazement, he found pockets of rich, fertile soil. Every Ecology 101 student knows that Amazonian rain forest soils are fragile and impoverished. If farmers cut down the canopy of trees overhead to clear cropland, they expose the earth to the pummeling rain and sun, which quickly wash away its small store of minerals and nutrients and bake what remains into something resembling brick—a “wet desert,” as these ruined areas are sometimes called. The certainty of wrecking the land, environmentalists argue, makes large-scale agriculture impossible in the tropics. Nevertheless, scattered along the Amazon River, Sombroek discovered big patches of < do preta>(black Indian earth). As lush and dark as the plaggen of his childhood, it formed a rich base for agriculture in a land where it was not supposed to exist. Naturally, Sombroek paid attention. His 1966 book, Amazon Soils, included the first sustained study of terra preta.
Later Sombroek worked across the globe, eventually becoming director of ISRIC and secretary general of the International Society of Soil Science (now International Union of Soil Sciences), positions he used to convene the first ever world survey of human-induced soil degradation. All the while he never forgot the strange black earth in Brazil. Most restoration programs, like those in China and the Sahel, try to restore degraded soil to its previous condition. But in much of the tropics, its natural state is marginal—one reason so many tropical countries are poor. Sombroek came to believe that terra preta might show scientists how to make land richer than it ever had been, and thus help the world’s most impoverished nations feed themselves.
Sombroek will never see his dream fulfilled—he died in 2003. But he helped to assemble a multinational research collaboration to investigate the origin and function of terra preta. Among its members is Eduardo Göes Neves, a University of São Paulo archaeologist whom I visited not long ago at a papaya plantation about a thousand miles up the Amazon, across the river from the city of Manaus. Beneath the trees was the unmistakable spoor of archaeological investigation: precisely squared off trenches, some of them seven feet deep. In the pits the terra preta, blacker than the blackest coffee, extended from the surface down as much as six feet. Top to bottom, the soil was filled with broken pre-Columbian pottery. It was as if the river’s first inhabitants had thrown a huge, rowdy frat party, smashing every plate in sight, then buried the evidence.
Terra preta is found only where people lived, which means that it is an artificial, human-made soil, dating from before the arrival of Europeans. Neves and his colleagues have been trying to find out how the Amazon’s peoples made it, and why. The soil is rich in vital minerals such as phosphorus, calcium, zinc, and manganese, which are scarce in most tropical soils. But its most striking ingredient is charcoal—vast quantities of it, the source of terra preta’s colour. Neves isn’t sure whether Indians had stirred the charcoal into the soil deliberately, if they had done it accidentally while disposing of household trash, or even if the terra preta created by charcoal initially had been used for farming. Ultimately, though, it became a resource that could sustain entire settlements; indeed, Neves said, a thousand years ago two Indian groups may have gone to war over control of this terra preta.
Unlike ordinary tropical soils, terra preta remains fertile after centuries of exposure to tropical sun and rain, notes Wenceslau Teixeira, a soil scientist at Embrapa, a network of agricultural research and extension agencies in Brazil. Its remarkable resilience, he says, has been demonstrated at Embrapa’s facility in Manaus, where scientists test new crop varieties in replica patches of terra preta. “For 40 years, that’s where they tried out rice, corn, manioc, beans, you name it,” Teixeira says. “It was all just what you’re not supposed to do in the tropics—annual crops, completely exposed to sun and rain. It’s as if we were trying to ruin it, and we haven’t succeeded!” Teixeira is now testing terra preta with bananas and other tropical crops.
Sombroek had wondered if modern farmers might create their own terra preta—terra preta nova, as he dubbed it. Much as the green revolution dramatically improved the developing world’s crops, terra preta could unleash what the scientific journal Nature has called a “black revolution” across the broad arc of impoverished soil from Southeast Asia to Africa.
Key to terra preta is charcoal, made by burning plants and refuse at low temperatures. In March a research team led by Christoph Steiner, then of the University of Bayreuth, reported that simply adding crumbled charcoal and condensed smoke to typically bad tropical soils caused an “exponential increase” in the microbial population—kick-starting the underground ecosystem that is critical to fertility. Tropical soils quickly lose microbial richness when converted to agriculture. Charcoal seems to provide habitat for microbes—making a kind of artificial soil within the soil—partly because nutrients bind to the charcoal rather than being washed away. Tests by a U.S.-Brazilian team in 2006 found that terra preta had a far greater number and variety of microorganisms than typical tropical soils—it was literally more alive.
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.”
Charles C. Mann is a correspondent for the Atlantic Monthly and Science.
Jim Richardson is an Honored Citizen of Cuba, Kansas, and 2007 Kansan of the Year.
The full story about Soil: http://ngm.nationalgeographic.com/2008/09/soil/mann-text/1
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Further reading about Terra Preta, Biochar:
1. http://www.bestenergies.com/companies/bestaustralia.html
2. An extensive source of background infos / links:http://www.shimbir.demon.co.uk/biocharrefs.htm
3. A PowerPoint Presentation on the science of Biochar:
http://ciifad.cornell.edu/activities/seminars/agroecsem/sem06/jmajor022206.ppt#272,9,Nutrient RETENTION
4. On line Forum:
BioEnergy Lists: Terra Preta (Biochar)
Information on the intentional use of Biochar (charcoal) to improve soils.
5. The latest info by Dr. Lukas van Zwieten, DPI – NSW, a 20 minutes radio interview recently completed on Biochar – the Wollongbar trials.
