The worst U.S. drought in half a century is sending global grain prices soaring. The fallout is almost certain to be felt at dinner tables across China. The No. 1 foreign buyer of American soybeans, which are pressed into cooking oil and used for animal feed, China last year purchased about half of U.S. exports, more than $10.4 billion worth, according to the American Soybean Assn. China has also stepped up purchases of U.S. corn and wheat to feed the nation's growing appetite.