"But there are many other vegetable crops that are eaten by people who are around the poverty level, so-called minor vegetable crops like eggplant, for which is there is no or very little data, " he explained.

BBC: 'Pollination crisis' hitting India's vegetable farmers

Autar Mattoo and his colleagues at the American Department of Agriculture's Vegetable Laboratory have been comparing mulching methods for tomato crops.

ECONOMIST: Genetic technology supports sustainable farming

Thanks to these subsidies and regulations, demand for maize and vegetable oils (on which biodiesel is based) has exploded and these crops have displaced others, such as wheat.

ECONOMIST: The real lesson from volatile commodity prices

On 5% of the world's vegetable-oil farmland it produces 38% of output, more than any of these other crops.

ECONOMIST: The campaign against palm oil