Kurt Kaser, 63, a life-long farmer in the central state of Nebraska, said he was working alone last month when he got out of his truck and mistakenly stepped into "that little hole" of the hopper.
"I about gave up once and just said the heck with it... and then I felt it jerk me again. I thought, well, I was going in," Kaser added.
He realized that his only option was to "cut it off" using the small knife in his pocket.
"So I just started sawing on it," he said, matter-of-factly.
After performing the grisly life-saving task, Kaser crawled to his house to phone for help, reports said.
The first to arrive was his son Adam, who happens to be a member of the local rescue squad, the Omaha World-Herald reported early Wednesday.
After a week in hospital and two more in rehabilitation, Kaser was back home last Friday, optimistic that he will be walking normally again, the newspaper said.
"I was in a hurry and didn't pay attention," he said, hoping his story can serve as a warning to other farmers.
Local media showed images of Kaser in a wheelchair, his bandaged left leg amputated below the knee.
The incident -- shared widely on social media -- prompted comparisons by moviegoers with Danny Boyle's 2010 film "127 Hours," in which James Franco plays real-life adventurer Aron Ralston, who amputated his own arm after being trapped in a canyon for five days.
Over on Facebook, Mike Walker, owner of Missouri-based Black Sky Radio, thought the drama was more reminiscent of horror film "Saw," an even more grisly take on self-amputation.
"I think I would have attempted to break every bit of whatever had me gorilla style before I went all 'Saw' on my parts," he posted.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)