That seed is germinating deep beneath an obscuring layer of thick, black soil.

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There is only a single track through the black-cotton soil cutting across an area the size of the Netherlands.

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Soon the trees disappeared, the gradient increased and the soil became black and powder-fine.

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The particular properties of the volcanic soil are ideal for growing purple potatoes, black truffles, buckwheat, white corn and tomatoes, and Nogue insists the ingredients have a distinct flavour profile compared to the same vegetables and grains grown elsewhere, a characteristic he attributes to the soil's perfect balance of absorption and porosity, as well as its mineral properties.

BBC: Spain��s Catalonia after El Bulli

France's celebrated victory on home soil at the 1998 World Cup, achieved by a team of black, white and Arab footballers, was widely hailed as a watershed moment for multiculturalism there, but few were still talking so complacently about social integration by the time the banlieues exploded into rioting in 2005.

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Black polyethylene mulching involves the plants growing through holes in plastic sheets that cover the soil.

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Lehmann, the lead author of the paper which is published in the journal Nature Geosciences, said that the black carbon content of soils in the study ranged from zero to 82 percent of soil organic carbon.

CNN: Soil study hints at climate model revision