BUENOS AIRES — U.S. farmers could receive cash payments from a planned $12 billion aid package as soon as late September, U.S. Agriculture Secretary Sonny Perdue told Reuters on Saturday, warning that the program will not make farmers whole.Perdue said in an interview on the sidelines of the G20 meeting of agriculture ministers in Buenos Aires that the plan would include between $7 billion and $8 billion in direct cash relief.U.S.