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"The river of cheap American corn began flooding into Mexico after NAFTA took effect in 1994. Since then, the price of corn in Mexico has fallen by half. A 2003 report by the Carnegie Endowment says this flood has washed away 1.3 million small farmers. Unable to compete, they have left their land to join the swelling pools of Mexico's urban unemployed. Others migrate to the U.S. to pick our crops — former farmers become day laborers.
The cheap U.S. corn has also wreaked havoc on Mexico's land, according to the Carnegie report. The small farmers forced off their land often sell out to larger farmers who grow for export, farmers who must adopt far more industrial (and especially chemical- and water-intensive) practices to compete in the international marketplace. Fertilizer runoff into the Sea of Cortez starves its marine life of oxygen, and Mexico's scarce water resources are leaching north, one tomato at a time.
Mexico's industrial farmers now produce fruits and vegetables for American tables year-round. It's ridiculous for a country like Mexico whose people are often hungry to use its best land to grow produce for a country where food is so abundant that its people are obese — but under free trade, it makes economic sense.
Meanwhile, the small farmers struggling to hold on in Mexico are forced to grow their corn on increasingly marginal lands, contributing to deforestation and soil erosion. Compounding these environmental pressures is the advent of something new to Mexico: factory farming. The practice of feeding corn to livestock was actively discouraged by the Mexican government until quite recently — an expression of the culture's quasi-religious reverence for maize. But those policies were reversed in 1994, and, just as it has done in the United States, cheap corn has driven the growth of animal feedlots, sewage concentration and water and air pollution."
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http://www.commondreams.org/views04/0423-02.htm