Iowa Agriculture Secretary Bill Northey said Thursday he won't run for the U.S. Senate next year, removing yet another top Republican from the list of potential suitors.

Northey said in an email that he plans to stay put.

"I feel at this time I can be more effective serving Iowans as the Secretary Agriculture rather than engaging in a Senate campaign," he said.

Northey joins a lengthening list of Republicans thought to be credible candidates for the seat being vacated by the retiring Sen. Tom Harkin, D-Iowa, who have instead taken a pass.

Also on that list are Rep. Tom Latham, R-Iowa, and Lt. Gov. Kim Reynolds.

In an interview, Northey said he was encouraged by what he heard as he explored a bid, but that he is closer to family and "I still get to run home and farm."

Northey also praised U.S. Rep. Steve King as a "strong conservative leader in Washington" who would he pledged would have his full support if he chooses to run.

Earlier this week, the congressman said that he is "embarrassed" not to have made a decision yet.

The delay has caused some discomfort among some Republicans eager to see the GOP field shape up — and who see Rep. Bruce Braley, D-Iowa, as a formidable candidate who has been raising money for months.

Still, Northey said he's not concerned about the delay. "We're still over 12 months away" from the Republican primary in June 2014, he said.

Northey said he alerted King to his intentions, but he doesn't know what the congressman might do.

Among those mentioned as possible candidates if King doesn't run are Secretary of State Matt Schultz, state Sen. Joni Ernst, R-Red Oak, Sen. Chuck Grassley's chief of staff David Young, former U.S. Attorney Matt Whitaker and former Reliant Energy CEO Mark Jacobs.

Many activists and analysts believe if King runs, he'll have the GOP nomination to himself. But the longer he waits to make an announcement, the longer that others who will run in his absence have to remain in neutral.

"Until he does (make a decision), nothing happens," said Brian Dumas, a GOP strategist from Davenport.

Republicans across the board have been bullish about their chances in 2014.

They say they expect Gov. Terry Branstad will be at the top of the ticket, and that the election will come two years from the end of President Barack Obama's second term, a time when the public often becomes weary of their president.

Some have noted Braley himself was elected in the 2006 Democratic wave that swept the party into the majority in Congress amid widespread dissatisfaction with President George W. Bush, who was in the last part of his second term.

"He is going to be running upstream this time," Dumas said.

Jeff Link, a top adviser to Braley, says any Republican bullishness is disproved by the continuing lack of a candidate.

"If they really feel like this is a surge year, a movement year, these candidates should be killing themselves to get in first," he said.

Braley, who early on declared his intention to run for the job, had more than $1 million in the bank at the end of March and has lined up an array of endorsements from labor unions and Democratic officeholders, including Harkin. The Planned Parenthood Action Fund endorsed his candidacy Thursday.