Brazilian farmers are in the midst of collecting their biggest corn harvest ever and American supplies are also plentiful -- setting the stage for a stiff battle to win world buyers in the second half of the year. It’s a turnaround from just a year ago when U.S. exporters were seeing sales boom as a drought plagued Brazil’s fields. This year, the South American growers enjoyed much better weather and crop supplies have gotten so big that farmers are already short on storage after collecting a massive soybean harvest just a few months earlier. That’s giving exporters incentive to push corn shipments out quickly and could mean a squeeze for hedge funds that are betting on a price rally.