RONDONÓPOLIS, Brazil — For more than 2,000 years, the Chinese have turned soybeans into tofu, a staple of the country’s diet.

But as its economy grows, so does China’s appetite for pork, poultry and beef, which require higher volumes of soybeans as animal feed. Plagued by scarce water supplies, China is turning to a new trading partner 15,000 miles away — Brazil — to supply more protein-packed beans essential to a richer diet.

China’s global scramble for natural resources is leading to a transformation of agricultural trading around the world. In China, vanishing cropland and diminishing water supplies are hampering the country’s ability to feed itself, and the increasing use of farmland in the United States to produce biofuels is pushing China to seek more of its staples from South America, where land is still cheap and plentiful.

“China is out there beating the bushes,” said Robert L. Thompson, a professor at the University of Illinois who is a former director of agricultural and rural development at the World Bank. The goal, he said, is “to ensure they have access to long-term contracts for minerals and energy and food.”