Southern farm interests flexed their political muscle in the Senate today, blocking an attempt to slash limits on what one farm family can collect in federal subsidies from $360,000 to $250,000 a year. It was the second defeat this week for lawmakers seeking to reshape the nation's farm programs, which contain billions of dollars in waste and loopholes, as a Post series has documented.

In today's action, a farm bill amendment drafted by Sens. Charles Grassley (R-Iowa) and Byron Dorgan (D-N.D.) garnered 56 votes, four shy of the 60 needed under Senate rules. The change was opposed by a solid bloc of Southern lawmakers, who claimed it would hit mainly rice and cotton growers left out of the ethanol-driven boom in the corn belt. "Farmers growing corn are making boatloads of money." said rice-state Sen. Mary Landrieu (D-La.).

Grassley and Dorgan were more successful during the last farm bill debate in 2002, when their amendment passed the Senate with 66 votes. It was cut out of the final bill, however, when House and Senate negotiators got together.

Today's vote suggests fading appeal for the payment limit issue even in populist-oriented Northern wheat states. Opposing the amendment were Sens. Kent Conrad (D-N.D.) and Pat Roberts (R-Kan.)

All four Democratic senators competing in the Iowa primary -- Hillary Clinton (D-N.Y), Barack Obama (D-Ill.), Christopher Dodd (D-Conn.) and Joseph Biden (D-Delaware) -- voted for tighter limits. Sen. John McCain (R-Ariz.) was absent.

Update: Later in the day, farm state opponents blocked an amendment that would have prevented farm subsidies to individuals with adjusted gross incomes over $750,000.

-- Dan Morgan