Seventeen-year-old U.S. student Charlie Rotering could hardly believe that a farmer in northeast China profited over 200,000 yuan (31,420 U.S. dollars) last year simply by planting sweet potatoes.

Rotering and nearly a dozen other youngsters from Highland Park High School and Deerfield High School in Illinois on Monday visited farmer Zheng Xiang's home in Liaoning's coastal Suizhong county as part of a China-U.S. youth exchange scheme.

While it allowed them to get a sense of what life and farming is like in China, it also opened up their eyes to how innovative modern agricultural and industrial practices are playing out in the Asian country and the world.

Zheng's farm is about 360 km to the east of Beijing, while the products made from his sweet potatoes have been sold so far and wide that they have reached Rotering's hometown.

The per capita annual income for rural residents in Suizhong was 6,736 yuan in 2010, but Zheng's family of six exceeded that a few years ago, when they started to plant sweet potatoes instead of traditional corn.

That shift took place when Huludao Maohua Biology, a private high-tech factory was established in town in 2008 to extract natural food colors like the red of sweet potatoes.

The plant offered seeds to farmers and collected all the sweet potatoes at a pre-contracted price, according to Liu Yubo, owner of the factory.

"That means farmers' income is secured even in major disasters", said Liu.

Compared with regular sweet potatoes, Zheng's plants were more purple in color, a trait generally considered a good indicator of healthy properties.

The factor owner proudly told the visiting students that Coca-cola was also on the business' client list and most of its natural products were sold to foreign food makers and used to improve the appearance of ice cream and cakes.

It's hard to imagine such a factory in remote countryside supplying products to food makers in the United States, said Rotering, adding that it is a perfect example of the global flow of goods and resources in today's "flat world" in which everything is interrelated despite physical distance.

Zheng, in his 60s, also shared his worries about the future with the teenage guests. His son and daughter are both working in town and Zheng's business partner is his only brother Ye. Zheng and Ye focus on managing their 200 mu, or 13.3 hectares, of farmland, and hire workers to do the daily farm work.

Ye's son is currently pursuing a bachelor degree in electronic engineering in the provincial capital and has not decided whether to come back to the farm or not.

Ye, however, expressed confidence his son could make more money working with him than in cities as an engineer.

The visit was designed to enable the American students to witness what is really happening in China, especially in rural areas, and to grasp some ideas about the huge urban-rural differences, said Huang Shuai, director of Youth Bridge China, the organizer of the event.