Gilmour discovered that Wakaya ginger grew well in the fertile volcanic soil near his house.

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The people who have returned consider the risk worth taking because their existence depends on the rich volcanic soil.

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Cappadocia has one of the world's oldest wine industries, which stretches back some 4, 000 years to the Hittites, the first to recognise the volcanic soil's viticultural qualities, and to carve rock cellars.

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Visit Ulupalakua, Maui's second largest cattle ranch, on the slopes of Mount Haleakala, where, in the mid-1800s, ranchers cultivated sweet potatoes, taro and sugarcane in the rich, volcanic soil.

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As we head back out into the paddy fields, he lights a clove-scented cigarette and points to the shadowy, still-active volcano that shares its name with him - Gunung Agung, the tallest, most sacred mountain on Bali, from which rivers are said to flow and the volcanic soil gains its rich fertility.

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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.

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Other former coffee-plantation land, high in the mountains where the soil is rich in volcanic minerals, remains overgrown with weeds and contains barren trees.

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