The head of the Environmental Protection Agency ruled out for now regulating runoff from farms in the Mississippi River basin, saying voluntary measures should be given time to work.

Agency Administrator Lisa Jackson, who visited two Iowa farms Tuesday with Agriculture Secretary Tom Vilsack, said she assured a gathering of agricultural leaders that the agency had no plans to impose pollution regulations like those being used to clean up Chesapeake Bay.

"I am ruling out the need for us to move directly to a regulatory mechanism when we have folks stepping up and are willing to do the conservation measures," she told reporters after the visits.