http://www.css.cornell.edu/faculty/lehmann/terra_preta/TerraPretahome.htm<snip>
Amazonian Dark Earths - implications for soil fertility and land useIn addition to their high soil organic matter contents as mentioned above, Amazonian Dark Earths are characterized by high P contents reaching 200-400 mg P/kg, and higher cation exchange capacity, pH and base saturation than surrounding soils (Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Glaser et al., 2000; Lehmann et al., 2003; Liang et al., 2006). These soils are therefore highly fertile (Lehmann et al., 2003). Fallows on the Amazonian Dark Earths can be as short as 6 months, whereas fallow periods on Oxisols are usually 8 to 10 years long (German and Cravo, 1999). Only short fallows are presumed to be necessary for restoring fertility on the dark earths. However, precise information is not available, since farmers frequently fallow the land due to an overwhelming weed infestation and not due to declining soil fertility. Continuous cropping for longer periods of time appears to be possible from a soil fertility point of view. How long a field can be continuously cropped and what can be done to prolong this period is not yet clear. Petersen et al. (2001) reported that Amazonian Dark Earths in Açutuba were under continuous cultivation without fertilization for over 40 years.
Recent efforts stimulated by Terra Preta research included the investigation of biochar (biomass-derived black carbon or charcoal) as a soil amendment to enhance nutrient availability and retention. Charcoal amendments were shown to significantly decrease nutrient leaching and increase crop growth (Lehmann et al., 2003), and the tests of slash-and-char systems were suggested as an alternative to slash-and-burn (Lehmann et al., 2002).
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http://www.sciencedaily.com/releases/2006/03/060301090431.htm<snip>
"The result is that about 50 percent of the biomass carbon is retained," Lehmann said. "By sequestering huge amounts of carbon, this technique constitutes a much longer and significant sink for atmospheric carbon dioxide than most other sequestration options, making it a powerful tool for long-term mitigation of climate change. In fact we have calculated that up to 12 percent of the carbon emissions produced by human activity could be offset annually if slash-and-burn were replaced by slash-and-char."
In addition, many biofuel production methods, such as generating bioenergy from agricultural, fish and forestry waste, produce bio-char as a byproduct. "The global importance of a bio-char sequestration as a byproduct of the conversion of biomass to bio-fuels is difficult to predict but is potentially very large," he added.
Applying the knowledge of terra preta to contemporary soil management also can reduce environmental pollution by decreasing the amount of fertilizer needed, because the bio-char helps retain nitrogen in the soil as well as higher levels of plant-available phosphorus, calcium, sulfur and organic matter. The black soil also does not get depleted, as do other soils, after repeated use.
"In other words, producing and applying bio-char to soil would not only dramatically improve soil and increase crop production, but also could provide a novel approach to establishing a significant, long-term sink for atmospheric carbon dioxide," said Lehmann. He noted that what is being learned from terra preta also can help farmers prevent agricultural runoff, promote sustained fertility and reduce input costs.
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The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropicshttp://www.springerlink.com/content/ch88m96jtrfrj4gk/Authors
Bruno Glaser, Ludwig Haumaier, Georg Guggenberger, Wolfgang Zech
1Institute of Soil Science and Soil Geography, University of Bayreuth, 95440 Bayreuth, Germany
Abstract
Many soils of the lowland humid tropics are thought to be too infertile to support sustainable agriculture. However, there is strong evidence that permanent or semi-permanent agriculture can itself create sustainably fertile soils known as 'Terra Preta' soils. These soils not only contain higher concentrations of nutrients such as nitrogen, phosphorus, potassium and calcium, but also greater amounts of stable soil organic matter. Frequent findings of charcoal and highly aromatic humic substances suggest that residues of incomplete combustion of organic material (black carbon) are a key factor in the persistence of soil organic matter in these soils. Our investigations showed that 'Terra Preta' soils contained up to 70 times more black carbon than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is chemically and microbially stable and persists in the environment over centuries. Oxidation during this time produces carboxylic groups on the edges of the aromatic backbone, which increases its nutrient-holding capacity. We conclude that black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.
Putting the carbon back: Black is the new green(Nature news feature)
http://www.nature.com/nature/journal/v442/n7103/full/442624a.htmlNews Feature
Nature 442, 624-626 (10 August 2006) | doi:10.1038/442624a; Published online 9 August 2006
Putting the carbon back: Black is the new greenEmma Marris1
AbstractOne way to keep carbon dioxide out of the atmosphere is to put it back in the ground. In the first of two News Features on carbon sequestration, Quirin Schiermeier asked when the world's coal-fired power plants will start storing away their carbon. In the second, Emma Marris joins the enthusiasts who think that enriching Earth's soils with charcoal can help avert global warming, reduce the need for fertilizers, and greatly increase the size of turnips.
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