Ambassador Islam Siddiqui, the chief U.S. agriculture negotiator at the Office of the U.S. Trade Represented , has decided to leave his post soon, U.S. Trade Representative Michael Froman announced yesterday.  Froman noted that Siddiqui played a key role in the Panama, Colombia and Korea free trade agreements as well as the recent World Trade Organization ministerial in Bali.  Siddiqui also served at USDA during the Clinton administration and worked for the California Department of Food & Agriculture and in the private sector.