Washington and Brasilia have agreed to expedite negotiations under the Brazil-U.S. Commission on Economic and Trade Relations with the goal of completing a trade agreement this year. The effort will politically split the agriculture sectors in both countries, much as it did when such an agreement was first discussed nearly two decades ago. The economics since then have shifted slightly but not dramatically.  In 2004, it was estimated that the U.S. would gain in a larger trade agreement with South America via livestock product exports but lose on feed grain and soybean exports. Brazilian corn production has tripled since then but remains just 28 percent of U.S. production and requires imports. Brazilian poultry production has increased...