U.S. President Barack Obama (R) walks around the McIntosh family farm with the owners to view drought-ridden corn fields in Missouri Valley, Iowa August 13, 2012. Leading members of the Group of 20 nations are prepared to trigger an emergency meeting to address soaring grain prices caused by the worst U.S. drought in more than half a century and poor crops from the Black Seabread basket. Benchmark Chicago corn rose to an all-time high on Friday after the U.S. Department of Agriculture cut its production estimate 17 percent. REUTERS/Larry Downing (UNITED STATES - Tags: POLITICS FOOD BUSINESS COMMODITIES AGRICULTURE)