"It's just the size of millet," said Johnson, who now lives in Bigfork, Montana. "I think the problem you get into in South America is getting enough land to justify a combine."
When he was growing quinoa in the late 1980s, the United States accounted for 37 percent of the world's quinoa crop, Johnson said. Today, it has about 2 percent, he said.
Environmental concerns about the expansion of quinoa in Bolivia aren't the only problems that experts see.
Near Lake Titicaca, in some of the highlands' most fertile soils, quinoa is now showing up where it hadn't before been planted, replacing potatoes, beans and oats in some fields.
Experts fear that trend could harm food stocks in this poor nation where one in five children suffers from chronic malnutrition.
And with quinoa now costing three times as much as rice in La Paz markets, it isn't eaten much by Bolivians. Its consumption averages a little more than a kilogram, (2.2 pounds) per year for each Bolivian.
The U.N. Food and Agriculture Organization hopes to promote more use of quinoa at home by promoting the serving of quinoa in subsidized school breakfasts.
Morales said at U.N. headquarters Wednesday that "it's not true that due to an increase in the price of quinoa less and less is being consumed" in Bolivia.
Domestic consumption is actually up threefold in the past four years, he said, to 12,000 metric tons.
Associated Press writers Carlos Valdez in La Paz and Carla Salazar and Frank Bajak in Lima, Peru, contributed to this report.
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