Behind the food riots: a debate on how best to farm

Aguila now sweeps floors in a Mexico City mall and marched in last year's protests against tortilla price rises.

The pain inflicted on Mexican farmers by NAFTA, the North American Free Trade Agreement, was supposed to be offset by cheap grains for consumers, said Jeff Faux of the Washington-based Economic Policy Institute. "But when the U.S. Congress realized the potential of ethanol, corn was diverted there and Mexico was left high and dry," Faux said. "The corn turned out to be not that cheap."

The campesino federation estimates 200,000 Mexicans a year have fled the countryside for the city or the United States since NAFTA was launched in 1994.

World Bank chief Robert Zoellick, a former U.S. trade representative, defended trade pacts and said they serve to lower world food prices, not cause them to increase.

"NAFTA is one of the reasons prices are not higher," Zoellick said Wednesday at a Mexico City news conference.

There are those who say it's not free trade that's to blame but the sudden seismic shift in the global economy -ballooning oil prices, a biofuel boom that is gobbling up farmland, and a voracious Chinese market for food. Get used to it, they say -the era of cheap food is over.

But Tyler Cowen, a professor of economics at George Mason University, recalls that the last big food price increase, in the 1970s, was followed by agricultural advances known as the "green revolution" that hugely increased the supply and brought down costs, and "If we don't mess this up we can expect the same today."

However, he worries that U.S. and European Union farm subsidies and tariffs, plus grain export bans and taxes triggered by the latest crisis, will make things worse.

Meanwhile, rice alone has more than tripled in price since January. Corn, wheat and other staples also have soared beyond the ability of millions to pay for a healthy diet.

Some blame price inflation on speculative trading of futures -contracts to buy or sell grains, metals, oil and other commodities at a set price on a future date.