Dwight Watson drove his tractor through the centre of the capital

Dwight Watson, 51, had been convicted of making false threats and destroying government property.

In March 2003 he shut down a section of the US capital when he parked his tractor in a pond on the Mall and held police in a standoff for three days.

He was protesting against US government cuts in subsidies to tobacco farmers.

The farmer from North Carolina claimed to have explosives, amid a heightened terrorist alert.

Traffic was diverted, some government offices were closed and much of downtown Washington was disrupted until Mr Watson surrendered, the Washington Post reported.

"Mr Watson, I have concluded you are a nice guy and you had a legitimate grievance," District Judge Thomas Penfield Jackson said.

"The sentence I will hand down to you today is intended to deter the next nice guy who thinks he has a legitimate complaint."

Mr Watson, dubbed "Tractor Man", has spent 15 months in prison.

He apologised in court to Washington for the fear and damage he caused.

"My question is, what do you do when the government is abusing you?" he added.