Flame weeding involves strapping a tank of propane to the back of a tractor and running specialized equipment down rows of crops, burning any non-crop stuff that gets in the way.
Here's a similar setup on corn that's been growing a while.
These are becoming popular with organic farmers. Via Carolyn, who shot the second video:
Dennis Luettke, an organic dairy farmer near Wells, MN manufactured our flame weeder. We bought an old anhydrous bar, and brought it down to Dennis for the burner kits and set up. We are in the process of converting a used sprayer into a flame weeder, mostly because of the frame style and wheel placement. We use 22″ rows on our corn and beans.